Become a Creator today!Start creating today - Share your story with the world!
Start for free
00:00:00
00:00:01
Heat Stress in Plants
168 Plays2 years ago
In this episode of Hort Culture, we'll talk about heat stress in plants and how it affects their growth and development. It can happen in summer, during heat waves, or in greenhouses. Some signs of heat stress are curling leaves, brown edges, dry soil, and reduced growth. To avoid heat stress, you should water your plants regularly, mulch the soil, shade them from direct sunlight, and choose heat-tolerant varieties. Tune in to learn more tips and tricks on how to keep your plants cool and happy.
Heat wave in the garden: How to identify and prevent heat stress in plants
High Tunnel Planting Date Calendars
Questions/Comments/Feedback/Suggestions for Topics: hortculturepodcast@l.uky.edu
Recommended
Transcript
Introduction to Hort Culture
00:00:02
Speaker
Welcome to Hort Culture, where a group of extension professionals and plant people talk about the business, production, and joy of planting seeds and helping them grow. Join us as we explore the culture of horticulture.
00:00:16
Speaker
Hello, everybody. Welcome back. We're
What is Heat Stress?
00:00:19
Speaker
in for a spicy episode today. We're all here, and we're talking about some heat stress today. We are not together physically today, so hopefully the traumatic experience will be de-escalated, just a little bit. For us and for the listeners out there, for both parties. I'm
Effects of Heat Stress on Humans and Plants
00:00:41
Speaker
glad you brought this up, Lexus, because I have been sweating a lot.
00:00:46
Speaker
And it is stressful and I am not so... Oh, you mean in plants. Got it. Today does have a red shirt on. We are talking to farmers, so, you know, we get hot to the past, I don't know, past couple weekends, it's been... Hot, hot heat. ... outside. I don't know if you guys have noticed, like, if you stand in the sun, it's hotter than if you're in the shade.
00:01:10
Speaker
yeah i think i think they're related there's something about the sun correlation for sure i don't know i'm going to say it's directly involved more more research is needed
00:01:23
Speaker
If I were a solar panel, a book by Ray Tackett. I imagine. Yeah, I'm always covered up in the summer, too. Everybody's like, how are you staying in that heat? Because I'm pale and in long sleeves and pants with a big sun hat on. I have learned to love like sun shirts, like truce, like sun shirts. I've grown to love them. We used to put up a lot of hay in the summer at 104 degrees with cotton shirts on. But then long sleeve, always long sleeve because, you know,
00:01:50
Speaker
Yeah, and I'm so glad that we have performance materials now, everyone. I do love that. I have a question. What SPF do the bald boys use on their heads? I almost always wear a hat, so I don't usually apply SPF. Oh, your hat? I'd go 50 plus for sure. OK, all right. I'm just curious. Yeah, I'd say the same. I want to make sure that we are protecting our skin here, folks. Just paint my forehead with aluminum paint. I don't actually do that. Aluminum paint? Just for the record.
00:02:23
Speaker
This is a plant podcast, not an alien podcast. Okay, so where did the plants come from in the first place? The chicken or the egg people, the chicken or the egg. Anyways, talking heat stress, talking spacing, heat today.
Heat Stress on Plant Types
00:02:41
Speaker
Yeah, let's talk about how plants react with some heat stress. When you aren't thinking about, you're talking about heat stress, are you thinking or initially at least thinking mostly about like annuals that you're wanting to talk about or are you thinking perennials as well? What's your- All of the above. Yeah. Yeah. Because it seems like there's a little bit of a difference between something that was just planted in the ground
00:03:05
Speaker
you know, four weeks ago versus something that... Yeah, absolutely. Or how about a perennial that was planted when it's really hot out that goes in the ground, which is, I know a different case scenario, but yeah, it seems like the perennial plants can handle the heat with a more established root system in some cases, in some cases, and especially those perennials that have, you know,
00:03:27
Speaker
deeper tap rooted system. Have you all gotten head questions from folks coming in about that seem to be related to the heat as far as their plants or pictures or samples or whatever? I didn't phrase it that way, but let's say on the perennial side, yes, because it seems like if you have bacterial leaf scorch or any of these other existing conditions, they always show up during drought conditions or extended dry periods.
00:03:56
Speaker
Basically, it seems like when it gets really dry that it unmask all the other existing problems with plants. I don't know. Yeah. We've been seeing a lot of winter damage that is shown in the past actually a couple of weeks. Absolutely. We're in the beginning of summer and we're seeing winter damage, but I think, so the question going back to like perennials versus annuals, I think
00:04:19
Speaker
A good place to start there is something that happens with both perennials and annuals. It's
Importance of Transpiration
00:04:25
Speaker
all plants and that's the act of transpiration. So I think understanding what transpiration is, is going to be the most helpful and understanding how plants are affected by heat stress and heat and drought. So I feel like those also need to be
00:04:41
Speaker
something we're talking about. We're talking about there's heat stress, which is caused just by the temperatures, but it could be raining every day, but you have really hot temperatures. But then there's drought stress where you can have a drought even when it's cold. I mean, we see a winter damage on a lot of our evergreens when we don't have a ton of precipitation in the winter and they go through drought stress. It's not just the cold. So I think often people want to think of those things as the same thing and they do often go together, but they are different from a
00:05:10
Speaker
Great distinction. Um, but transpiration. So this is just always helpful, like for me and understanding and thinking about how the plant works. So perennials, annuals, right? They all have roots and they're all going through a process called transpiration, which is part of a photosynthesis.
00:05:28
Speaker
And so transpiration is essentially just the loss of water through the leaves of a plant. It's through what's called the stomata, which is just their pores. So it's essentially kind of like they're sweating, right? If you want to put people characteristics onto plants, so they are sweating. The plants are transpiring. I like to say, I'm not sweaty. I'm just transpiring.
00:05:51
Speaker
when I'm outside. So transpiration. That's one on my transpiration board. Transpiration board on Pinterest.
00:05:59
Speaker
Exactly. So, 90% of that water that that plant takes up is lost through transpiration. Okay. And so that is necessary, that transpiration is necessary because that movement of that water and that pressure being taken out through the top, if you were like watching me right now, I know we're on a podcast. My arms are doing some things right now. A lot of gesturing. Is that the YMCA?
00:06:27
Speaker
Picture a column of water. Right. A column of water from the root system that water is being lost through the leaves, through the top. And because of that, it is able to pull up water from the root system. So there is some gas exchange and stuff that happens, you know, in the leaves, blah, blah, blah. But the main focus here is that in order for the plant to pull water from the soil, it has to lose water in the leaves.
00:06:53
Speaker
And a real another important thing about this is we see a lot of nutrient deficiencies when a plant is not able to access water for a couple different reasons and we'll go into that but nutrients go in through the water through water right through the root system so if it's not able to pull up water it's not able to pull up those nutrients and so people want to throw fertilizer on a plant because it's looking nutrient deficient
00:07:17
Speaker
But really, it's that your soil has plenty of nutrients in it a lot of the time. It's you're not getting enough water. And that's like a good example of that is like blossom and rot. You're not watering consistently enough to pull that calcium up into the plant. Yeah, I tend to think of that that kind of transpiration or I always use evapotranspiration because it's a longer word and it makes me sound. Right. I'm really cool. But it has that evaporation kind of component built into it. And that
00:07:45
Speaker
That whole process is kind of, I mean, it is critical to like the plant's metabolism. Like as you say, it's helping draw the nutrients in.
00:07:54
Speaker
It's helping things mobilize and move up through. And I mean, even at the point where it is lost into the atmosphere and it's evaporating, there is a little bit of cooling that's happening to the plant tissue. So it's a way that the plant tries to regulate its temperatures through that. Because unlike us, plants can't go hide in the shade or put on a hat. They're kind of stuck with what the sun and the elements are doing to them.
00:08:21
Speaker
I guess we'll back up in just a second. We're talking about heat stress. And we're going to talk about averages here. I'll ask you guys about this. But the average range, above what temperature do we start to see heat stress? What's the average optimum for zone 6, 7?
00:08:39
Speaker
you know, roughly kind of where we're at here in Kentucky, the central part for Kentucky overall, really. But like, what's an average range where if we get outside of that range, we start to see heat stress? I mean, is there any averages that you guys typically go by? I know when I'm working with commercial vegetable producers, we definitely have a range in mind.
00:08:59
Speaker
I don't know if it's different for flowers, you know, under 90 as well, like for field vegetables, but is that different depending on some of the crops you guys deal with? So I like to think of them. There's a reason we have cool season plants and warm season plants as well. So, you know, peas are going to have a different, uh, snow peas are going to have a different growing amount than beans or something like that is. But I know.
00:09:24
Speaker
And this is, I only know this because I looked it up in preparation because we prepare for you people. We want you to know there's a lot of work that goes into this rambling. Alexis is being modest. It's all in there in her mind at all times.
00:09:47
Speaker
I know the ideal, like in a perfect world.
00:09:55
Speaker
For tomatoes and peppers are an example that I'm going to go with because it's kind of something that everybody grows. They are warm season, but they actually, I was surprised, ideally like it a little bit cooler than I thought they would. So those perfect temperatures are between.
00:10:11
Speaker
for those are between 68 and 77 degrees Fahrenheit, which I was cooler than I thought it was going to be. But then it makes sense when we start to see temperatures above 80. And it's not saying that your plants not going to grow. We're talking perfect, you know, scenario here optimal optimal. Thank you.
00:10:28
Speaker
But above 80, we start to see problems and above 85 is when we really see a hit on crops for the most part. I would say even in the flower world, even those warm season crops will slow down in temps that are between 85 and 90.
00:10:45
Speaker
you know, if there's not enough moisture and it kind of comes back to also humidity in the air, which we've... I don't want to like jump too far off of this where Ray was going. I'm going to circle back to humidity and how that affects transpiration because it's very exciting. Yeah. So I've always thought about it as like 75 green light, 80 yellow light, 85 orange light, 90 and above red light.
00:11:11
Speaker
Yeah,
Impact of Heat on Vegetables
00:11:12
Speaker
above 90 for an extent about a time pepper squashing cucumbers, you have blossom. All the blossoms dropping off or a large percentage until it cools down. So you just straight start losing percentage of crop. That's the red zone, right? And nighttime temperatures factor into I think if it's cooling off versus
00:11:32
Speaker
just staying hot like some of those times in July where you walk out at 6 a.m. and it feels like 6 a.m. It's 80 degrees. Just soaking humidity. On the commercial side of things too, if you really notice, I mean temperature is so critical, but also as an indication of where the plant is and the stress that it could possibly be under the amount of product if you're doing like an insect or weed control, if you look on the labels,
00:12:00
Speaker
of a lot of commercial chemicals, or even homeowner chemicals, there will be a temperature warning on there that will say, if you're applying, let's say, to a cool season lawn, a weed control product, it'll absolutely say, do not apply above this temperature, or you're going to damage the crop that would otherwise be perfectly safe to put that product on. So yeah, temperature, and that tells us a lot about both the product that you're putting on, not only that, but the stress that the plant's under. So yeah, temperature
00:12:28
Speaker
So very important, once things get heat stressed, lots of bad things happen. Yeah. Yeah, I've got.
00:12:34
Speaker
a publication here from Oregon State that this is addressed to people who are, you know, gardening, lawn landscaping, flower shrubs, trees, and they give kind of a blanket. Most plants grow best 59 to 86. And then they start giving the warnings above 90. And then I have a little reference document that of course anyone can get.
00:13:00
Speaker
that has optimal ranges and kind of more for minimal, but it gives you your optimal. But yeah, it's the CCD high tunnel planting day calendar you have there, Josh. Right, right. And that is, of course, for somebody who's trying to manage for low temperatures, but it does give you the optimal range of what you want to what, where you're getting your target growth. And so above that, you know, you're going to have problems with
00:13:22
Speaker
nutrient transport or trying to look, one of the recommendations I saw was, you know, as you say, when you see these signs that indicate, uh, like a nutrient deficiency, that what is really going on is, you know, the lack of water. And one of the things that you could, something to not do is to apply fertility at that time. Right. You're just exacerbating the problem. Yeah. It's funny how a lot of these,
00:13:50
Speaker
a lot of these problems we think of these plants and we sort of attribute a certain amount of like agency or intentionality or whatever to those like the ways that we do you know if I get hot I'm gonna
00:14:01
Speaker
As I discovered this past week, I'm going to go in the shade instead of the sun. But a lot of the issues with plants are the ways that plants function. They're this blend of physics and biology and chemistry and biology. I mean, these are artificial constructs. We separate them all out into the things we call sciences. But to pull it back, Alexis, to that physiology thing that you're talking about and the transpirational process. So correct me if I'm wrong here.
00:14:30
Speaker
you're saying that leaves are transpiring. That creates this like pull, kind of like a siphon on a hose. It creates negative pressure that pulls water up to the roots. So the more leaves that a plant has, the greater the pressure and the more water it's moving. Is that right? I'm connecting this to, I think, I don't know if it's true or not, but it's one of those things that I've heard and seen is that people tend to overwater their plants in the spring or when they're young.
00:14:58
Speaker
They tend to underwater them once they're mature. If we're thinking in addition to the heat and the process of how that's driving transpiration and evaporation, also think about an older plant. It's got way more leaves. It's got way more little straws sucking on that water column to pull water up through the roots. Yeah, that makes a lot of sense.
00:15:21
Speaker
You know, it's not that the plant is like, Oh, I need more water. I consciously, I need more water in my leaves. So I'm going to initiate the pumps. It's actually this much more passive and elegant way of moving water and doing things and responding. And so what happens, so what's happening with heat stress partially is this is a question is that something about that mechanism is disrupted or is, is impeded. Is that right?
00:15:49
Speaker
So I think, yeah, so heat stress, I'm going to cycle kind of back into that humidity part of this, because I think that at least in Kentucky, right? We, we always say you're going to, you're going to boil. You're not really going to fry in the frying pan. You're going to boil in a bottle of water here because the humidity is so high. So we are all just two. I am. I have both myself. I have bold like a peanut before. So I can relate.
00:16:19
Speaker
We're all just frogs slowly beginning our boil. You won't notice, so it doesn't matter. Just do it gradually. Just do it gradually. The frog and the bowling water. Yeah, gradually. You turn the table drops slowly, please. One problem I see, I think, with heat.
00:16:35
Speaker
in water, so water is more related to, it's kind of that drought stress thing, so as well as heat. They're all connected, but they're separate, right? We kind of mentioned that, but I want to circle back to humidity kind of while we're at this point of, so sometimes we have these times of year where we have very high humidity in Kentucky, right? Just obnoxious, but we also have that partnered with high temp, so we're going to say above 85, which we know is a danger zone.
00:17:04
Speaker
for plants.
00:17:06
Speaker
But we may be getting plenty of rain because we have that humidity and we still see plants that have nutrient deficiencies, but also may look like they are not getting enough water. So sometimes that can be like root disease problems, but sometimes that is because that negative pressure we talked about, that siphoning that's coming out of the leaves cannot happen because there's so much water in the air that you're not getting enough negative reaction to pull it out of the soil.
00:17:36
Speaker
Your plants still will probably not will in the same way as it would if it's you know, 90 degrees and bone dry outside but we will see nutrient deficiencies especially even if the plant looks okay because it's not pulling and water often enough to pull in those minerals because the humidity is so high we're not having that negative pressure happening. That's sort of like and that's like if I go out and work.
00:17:59
Speaker
outside when it's hot and it's dry out, my clothes stay relatively dry because my sweat is evaporating. I'm not sweating any light versus the days I'm looking forward to in July that now I will mentally think of myself as boiling alive.
00:18:15
Speaker
When my shirt, I walk out and within 15 minutes, my shirt is soaked and the rest of the day I am just shedding water drips, not evaporating. It's
High Tunnels and Temperature Issues
00:18:25
Speaker
kind of a similar thing that at the leaf surface, because it's so humid, it can't evaporate because of that, that concentration of water in the air is too high. Right. Right. Right. Cool. And we see mostly nutrient deficiencies then.
00:18:40
Speaker
I do. We see a little bit of, you know, that water loss, but there's usually enough water in the air that it's kind of keeping everybody a little bit more happy. And you won't see a ton of drooping on your plants. I'm friends with you nerds as the, as the resident cool guy.
00:18:56
Speaker
We see this in high tunnels a lot. Yeah, high tunnels a lot. Every high tunnel I've looked at in the spring, and I've made several site visits to multiple high tunnels, and it's not unusual. For tomatoes, I'll pick on that crop, physiological leaf row. I mean, sometimes in a certain way, in a circular way, it can be related to high temperatures. Also to soil moisture, but a lot of those, they had plenty of soil moisture.
00:19:21
Speaker
But we see corn will roll out in the field. You can just pick out when it starts to get dry, use that as an indicator crop as I'm just driving by. I'm like, yeah, it's starting to get dry because- So what's the aspect of tunnels that makes it specific?
00:19:35
Speaker
Temperature variations there can relate to that and the way that the plant is, I mean, because past a certain temperature, you're going to shut down the plant straws. The mechanisms, the stomata mechanisms that control all of that. I mean, stomata is kind of cool. They can give off and take in moisture. That's the cool thing about those. I don't know, Alexis, did you find that? I mean, we talked to Master Gardeners a lot about
00:19:58
Speaker
We don't rely on them to take in a lot of moisture, but that mechanism is just disrupted. And it's not only sustained high temperatures, but the high-low temperature variation differential. They can also hold humidity too. Highs time. And it's really calm. You can go down a rabbit hole when you're talking about this stuff.
00:20:21
Speaker
But as we're talking about this, what do you guys look for? I mean, it's easy to say a plant has heat stress, but what does that look like maybe for the homeowner that may not be accustomed to looking for such things? I know I look for leaf rolling and cupping or sometimes yellowing. Of course, wilting, but it's more complicated than that because wilting is not always an indication that there's a lack of moisture.
00:20:46
Speaker
or that the temperatures are too high. So you kind of look for a variety of things. What else do you guys look for when we're talking about heat stress? Once I started working with plants, I think realizing that wilting is, you know, it's obviously not good, but it looks so much worse than it is sometimes. Yeah. That you're like panic. So I remember we had, back when I worked in the research side planting, we had some watermelons we had to plant on black plastic.
00:21:15
Speaker
And it rained and rained and rained and rained. And then there was this three-day window where it had dried out enough that we were able to get these things in. Well, it just so happened that that same window was like it jumped up to 89 degrees for three days. So we put these transplants in, had to get them in, and they looked like death.
00:21:37
Speaker
Right. Black plastic, hot. Did everything we could to try to... And then... Which that's a whole other problem. The plastic itself can get so hot above 90 that you're going to... What? Did you guys experience that way? Well, three days later, they perked right back up. We got some rain and everything was fine, but it was one of those moments of... Again, and when you're doing stuff, you don't want to make that a practice because every... Alexis was, I think is going to talk a little bit about like...
00:21:59
Speaker
Stress can be this cumulative thing where a stress in one area opens up the plant to vulnerability in other areas and you don't want to do that because a plant that gets super heat stressed next to a plant that didn't go through that, the plant that didn't go through that's going to have a head start to grow better and do better in general, just like a human being, you know, someone who's... Yeah, like you see all this weird like bolting and just all these reproductive changes in the plant. I've heard people refer to that as well, the tomato plant got age on it.
00:22:28
Speaker
and i guess that's their simplified way of saying that it went through these stress cycles and i guess it did literally get physiological aging lightly distressed stress connected to a lot of city miles yeah a lot of stop and go mileage on that tomato yeah you don't want the tiny tomato that's blooming folks just a word to the wise one of the things we kind of already hit on it but
00:22:53
Speaker
that I get a lot of questions on around mid July. Cause it's when we get so hot and in through August is my bean plant, my squash plant, my tomato plant, whatever name, name a, name a plant, to be honest with you is, uh, Oh, sorry. My persimmon plant, my persimmon plant, any hot weather, any, but anyways, it's, they've stopped fruiting. Like I'm not getting, I'm not harvesting off and anything, but the plant looks healthy.
00:23:21
Speaker
You know, they probably did everything right. Maybe they did a soil test, they've been watering well, they've been doing all those things, but they're not getting any fruit. They're like, you know, I get blooms, but I don't get any fruit off of it. And that's, like we've mentioned before, once we reach those temps, those inflorescence, inflorescence is just a fancy way of saying the flower.
00:23:41
Speaker
the inflorescence aborts on that plant. So that pollen dies, you know, the seed, the egg that creates that fruit dies, you know, whatever it is. And so you'll get blossoms and blossoms and blossoms, but you don't get that any fruit to form because it aborts before you get to that point. Or, you know, you'll get like a little like on squash, you'll get something that's like the tip of your pinky little looks like a little squash. And it's because it started when it was maybe cooler and then it got so hot that it aborted before it could kind of
00:24:11
Speaker
So that's one thing I see a lot of. So if you're not getting fruit but your plant looks healthy and you're getting blooms, that could be one reason why if you look back on the temps. In some cases though, once temps come back down a little bit or if there's a break, you might have a plant that will put on blooms that will mature into fruit. Right, right, right. Just keep it healthy, keep it happy and once temps come back down.
00:24:35
Speaker
you'll get that fruit to start again. So that's one thing for those. That you already have that are stacked up on your countertop like me. It's giving yourself a break. Yeah, it's giving you a break. From a very practical field standpoint, let's pick on tomatoes. If something's going on with your tomatoes, and I've seen this in very hot years, but if your vines don't have good physical vine coverage, then you have fruit that's exposed to
00:25:01
Speaker
to hot summer sun and then you just get sun scald, which in turn makes, can make blossom end rot even worse. But it's sort of one thing leads to another. It's like a domino effect. If something has affected your plant growth for a number, you know, for a length of time and it's not growing well, I mean, that's true of grapes or any other thing where it takes leaf cover to cover fruit, blackberries that you can include that in there as well. Not only that that has
00:25:28
Speaker
That has to do with where you plant those slope orientation and all of that. But if the plant's not healthy and doing well, you see all of these other things show up as a result of things like heat stress where the plant's not growing in an optimum way. And you just get all of these other fruit conditions that show up mid and late season. And that's just from a purely
00:25:49
Speaker
you know kind of field facing perspective but that's one of the first things I look for is to see what kind of leaf cover a particular plant has as I'm doing diagnosis and try to figure out what's causing sun scald because that's not a normal that's not a normal situation to have sun scald because plants have evolved away in which to protect those reproductive structures in essence so but we see that as a function of heat stress too in the long game so so far we we think about the like
00:26:16
Speaker
we've mentioned, you know, sunscald or fruit damage in general, that's one thing that happens as a result of heat stress. Alexis, you were talking about, you know, flowers aborting or blooms dropping. That's another component of that. Some wilting is it can be can be evidence of that it could be something else. What about like, like leaf curl?
00:26:38
Speaker
Yeah, I think Ray had mentioned leaf rolling and cupping and one kind of leaf edges looking at them. Margins are very different. The margin is the outside edge. Yeah, it's kind of a survival mechanism that they can sacrifice some of that. But I like the wilting is kind of a troubling one because
00:27:01
Speaker
you know, can indicate that there's not enough air down by the roots, right? Like, so it's kind of a symptom. Yeah. A symptom of over watering. So it, it can be unreliable in those kinds of systems. And while we're, while we're here on the, you talked about the roots, this is something, you know, again, all these three people are more, much more plant people than, than I am. I'm catching up gradually here in my, uh, in my thirties and learning, but the,
00:27:26
Speaker
The fertilizer thing, um, it looks bad. Let me, and it looks bad because there's not enough water moving up to the leaves, carrying nutrients for one reason or another. Let me just put a bunch of fertilizer and inspire the plants because it can just smell that down. In that case, what my understanding of what's happening, you all correct me if I'm wrong, is that you, if you think about like, we know that in environments where you have a high concentration and a low concentration right next to each other.
00:27:57
Speaker
the low concentration area that water is gonna move to areas of higher concentration. So in essence, you're creating a little saltwater bath with the fertilizer that your roots are now soaked in and it's gonna draw water out of the roots. Does that sound reasonable? In some cases it's possible because you could get it, that's a whole nother discussion is like soluble salts and soils and how that affects positive, negative uptake and all of that stuff. So why not why don't fertilize?
00:28:26
Speaker
The reason I, from a field perspective, once again, that I recommend people, and this, you have to look in the crystal ball ahead two to three weeks. If you see an ongoing, very hot weather pattern, I advise people to back off from particularly nitrogen because that's one of the macronutrients that promotes excessive top growth. Well, what you're going to have in that situation is a lot of tender growth.
00:28:48
Speaker
with very tender leaves that don't have, you know, develop lamina on the leaves. And you're going to get burn, physical burn. If it's hot and dry, you're going to, and you're going to lose that growth. So it's better to back off it, but you have to look in the crystal ball a little bit. And that's more on the commercial side. It also applies to homeowners. If you're fertilizing, you know, your annual flowers, you have to be careful about promoting a lot of tender growth.
00:29:11
Speaker
Not only for agents, which also love it, but you have to be careful when you see hot, dry weather coming up. I really work with my commercial producers. I'm like, have you seen the forecast for the next two weeks? It's supposed to be super hot. Just back up a little bit on your fertigation. So that's one of the reasons I try to...
00:29:28
Speaker
you know talk to people about that it's one of the ways it's a it's a desirable conditions for new growth to be able to kind of grow healthily but what you say about you know there are fertilizers that are essentially salts and that that can be real when you apply some that it'll suck the water right out of the plant tissue
00:29:49
Speaker
which is the opposite of what we're looking for. Right. Right. You also just waste it. Like, you know, even, even if that like instance doesn't happen or doesn't happen to a great enough extent to cause a problem of problems, it's just, you know, on a larger scale, it's just going down into the water, you know, water table. And we got, I'm sure that the algae in the Gulf of Mexico would disagree with the fact that it's wasted. They like to get big on that. Yeah.
00:30:16
Speaker
I mean, you know, the problem is that the
00:30:22
Speaker
If there's a lack of water, the nutrients aren't gonna even get into the plant anyway, right? The column isn't pulling them up, so. To add insult to injury, here's the worst, by far the worst thing to me, because it messes with me on a personal level. But,
Strategies for Managing Heat Stress
00:30:38
Speaker
and I will pick on home lawns. Cool season lawns, which are predominant here in Kentucky, is we tell people not to fertilize in the summer if you don't have irrigation. If you're on a high level maintenance schedule that has irrigation and all that, so be it.
00:30:50
Speaker
We can work with you, but typical homeowners don't have that. We tell them not to fertilize in the summer. They come back and say, why? Well, there's lots of good reasons. My number one reason is you're fertilizing that grass at a point where it's not normally doing a whole lot because it is, as Alexis said, a cool season grass. Not only that, but you'll have a much better response curve from the weeds that are competing with the desirable crops. We see that in the summer during during the hot, dry spells.
00:31:18
Speaker
That's another reason that if you're broadcasting or side dressing any kind of fertilizer, I'm like, be very careful because think about what's going to be able to have a competitive advantage from that. A lot of times the crops that we deal with that we're selecting for, that we've planted for whatever reason, they don't deal with the heat.
00:31:38
Speaker
and stress as well as weeds do, like something like sun grass, like a C4 to category plants that just love that, love hot, dry conditions. It doesn't bother them. They have roots 12 to 15 feet deep. You're fertilizing the weeds during hot, dry spells. So be very careful about your fertilizer. So on that, just a very brief aside on the, you know, extension recommendation side of things, if I want to build out a landscape
00:32:06
Speaker
that I have to be less concerned about heat stress about other types of plants that I would want to select. I might just put some, you know, amaranth and
00:32:17
Speaker
Johnson weed out, you know? I mean, Johnson grass out, right? No, probably won't do that. This is a huge... You might really have to mow it hard. Are there plants that have a little more resilience to... Absolutely. Absolutely. It is a massive topic out west and I saw a lot of presentations scheduled for our National Professional Association.
00:32:39
Speaker
Out West, as we all know, they've been through some cycles in the past, in the recent past, where they've had extended dry spells. And, you know, a lot of those developments are in deserts. So, yeah, I think it is. Zere escaping. Yeah. It starts with an X. It's a strange word, but basically, Brett, it's working with those plants and there's available lists that do better without any additional irrigation. And I love those lists. That's a great point, Brett.
00:33:07
Speaker
Yeah. Yeah. Cause a lawns can be very thirsty in terms of like how much water they want. So drought conditions, you know, are real hard on them and they make it hard on anything else you're growing. If you notice out in our cool season lawns, a lot of times the only thing that's going to be during extended hot dry spill, the only thing that's going to be green out there is something like a white clover or clovers that just deal with that better. You can pick out all the weeds because they're the only thing that's a nice green.
00:33:36
Speaker
dandelions that are tap rooted, they're green for a reason. So yeah. So to Alexis's point earlier, we are we are kind of now starting to mix heat and drought stress as these two kind of slightly different things. But I mean, are the primary mechanism is, you know, as always me asking my plant friends, like is the primary mechanism an issue for heat stress, the fact that water is not moving through the plant enough?
00:34:03
Speaker
one of the big issues. Yeah, I would like to say, you know, you don't get those a lot of those molecules, those nutrients moving through the plants properly and we get all sorts of deficiencies. So the so the different there are other things going on, like it messes with plant metabolism and creating ATP and stuff like that. But I think if I had to lay money on it, I'd say it's interference with water movement and transport. And so in that in that case, we're talking about times where it is really, really hot.
00:34:31
Speaker
There may be water in the soil, but it's so hot that the plant can't mess with it, which is different from it's just been really dry and there's no water there for the roots to suck up anyway.
00:34:41
Speaker
And a good indication is you'll see something like a, oh, I don't know, like a hydrangea. The old fashioned hydrangeas are a little bit worse for this. They're really wilt during the day, but they'll come back during the night. They'll shut down when they need to to protect themselves during really hot times I've noticed. But, and people say, oh, is that going to hurt the plant? And my question back to them is, are you experiencing sunscald? Because a lot of times when you lose pressure in the leaves, it wilts.
00:35:05
Speaker
If the plant's not designed to survive through those conditions, you'll get sunscald and that's going to, you know, enough sunscald. You lose a synthesis and stuff. Yes. You have leaf damage and you lose the energy factories, the leaves in the plants. But I noticed, and they say, no, we don't see any discoloration on the leaves or any burning of the leaves on the margins or in between. So I'm like, it's probably fine then. It's probably fine. It's just going through a cycle that it evolved to manage. Right.
00:35:34
Speaker
How about I got a question for the kind of group, is there a practice you recommend that is safe for helping plants going through heat stress, right? Like, we've already talked about watering might be kind of dicey if they're already being overwatered, you're not sure what's going on there. If we do that, we don't do it for the water and commercial turf, we do it to cool the soil to get a more optimum environment for cold season grasses, which
00:35:59
Speaker
But they're like, why are you watering it just, you know, it's hot out, but we've had plenty of rain. Well, that's not the point. It's to cool the soil. So that's a little bit to that in a very specific scenario. But now commercial turf, they do that all the time for the cooling effects.
00:36:14
Speaker
Other like non turf plants, we always say mulch is keeping the, keeping the, it's keeping the soil moisture consistent longer, but it's also keeping the temperature consistent longer. So when you have those cool times, it's staying cooler longer.
00:36:31
Speaker
Or, you know, in winter or spring, it's saying, you know, warmer, longer, but the moisture is the same way. And I think that the moisture, both the moisture and cooling aspect, um, play a lot into that nutrient movement and keeping those nutrients and that water uptake more consistent for happy, you know, those roots are happier. So you're getting more consistent.
00:36:53
Speaker
water and therefore nutrient uptake in that way. Now it's not going to help it if the heat is killing your blossoms off but your plant will be healthy so that when that heat does drop and you're allowed to you have blooms you know returning you're gonna have a really happy plant to produce more fruit. So yeah in terms of in terms of like landscape stuff I think you know to your point Josh or to our discussion one of the previous weeks maybe last week about ecosystem services you can
00:37:22
Speaker
protect plant, you use taller plants that are a little more robust to protect other plants from the really hot afternoon, late afternoon and evening sun, you know, that they're going to get mostly sun most of the day. But the backside of that western, western edge, you could have a deciduous plant or something that might grow up and be able to let light through in the spring more and then it fills out and then protects in the afternoon. I think that's part of it. Alexis, you have any shade cloth in your repertoire?
00:37:52
Speaker
Yeah, so I use shade I've used shade cloth on on my high tunnel Most people do when in the state, you know starting in June it needs it should have already been on by now It's not on yet But yeah, that's that's a good way to just kind of cut back on a little bit of that heat It never seems like enough at least when I'm personally in there. I'm just like is this working at all? but but it does work to just kind of shade out those plants and and keep the
00:38:20
Speaker
Keep that Sun from creating scald Another what percent do you brought it up in it? What percentage do you I think I've got 30% Yeah, which is kind of a standard I think for at least a lot of the crops that I'm growing 30 to get like a good tan I see 30 to 50 depending on what it is whether you're trying to
00:38:42
Speaker
Cause some people will try to, in a nursery environment, they don't have natural shade, so they'll put shade cloth on to grow their hostas in a, you know, structure. But anyway, I was just curious. Yeah. I was, I was thinking of when you brought up using other plants, shade, younger plants this, this year in my perennial rows. So I grow large quantities of a variety of, of perennials. And I have this one it's,
00:39:09
Speaker
It's called Aruncus. It's one of our natives. It's A-R-U-N-C-U-S. Sounds like a European rock. Aruncus. I'm just throwing out that. Aruncus. It's a common name. I think I saw them in Berlin. Hello, Aruncus. We love you. The common name is goat's beard. That's their first home. So it's a good one. It can get to be kind of a large flowering shrub, but it has these sort of ferny looking leaves almost.
00:39:37
Speaker
It really prefers to be in partial sun, like it wants to have morning sun and then that's it. But when I had it, I kind of wasn't thinking about it and I put it in a full sun area and it gets hot and it blooms around this time of year. So it's, it's, we're usually, we have hot days, you know, we've been in the night. We've had the degrees and degrees in the nineties days in the nineties, um, lately. And,
Benefits of Weeds and Mulching
00:40:00
Speaker
uh,
00:40:00
Speaker
So anyways, this year I didn't get to weed that row like I normally would. And I had this wild geranium come up and kind of engulf the plant. And wild geranium is definitely not the worst weed if you're not familiar with it. But it's, you know, it kind of gets big, but it lets a lot of light through. Those geranium leaves are kind of lacy. It does let a lot of light through.
00:40:21
Speaker
It kind of got big and it engulfed, right, this runkus. And what I noticed, I had a lot more blooms this year. And I was like, what the heck? And I had no leaf scald on it. And last year, you know, I had a decent amount of blooms, but, you know, around this time I got really bad burn around the edges because it prefers to have a shadier afternoon, as we all do. I love a shadier afternoon. But because I had just enough shade from this weed,
00:40:45
Speaker
of wild geranium, I didn't have that pressure on them. The plant is much healthier. And so I don't know, I just, I feel like I need to say this for those of you who are fighting the weeds right now. Sometimes it's okay and be more gentle with yourself. All right. Cause you may, you may get, you may get some good, something good come out of it. You may learn more about competence. Right. Nice. Nice. Um, make sure it finds a way.
00:41:12
Speaker
that the the geranium was just giving them a hug yeah it was like hey let me let me shade you bang yeah come here hang under my shade nature will find a way who's that malcolm said that on original jurassic park i think so yeah
00:41:29
Speaker
Classic documentary about nature. Yeah. Chaos theory. You were thinking about pulling that Dranean. You were focused so much on whether you could. You didn't ask whether you should. I see we have some other fans in the group today. We have some fans. It seems like it's tough during the discussion. It just made me think about some things because that is two different things that we're talking about here. There's the heat and then there's actually the available moisture in the soil. The two are different.
00:41:58
Speaker
And I guess that's it. I'm hearing that from all of you guys is that two distinctly different scenarios. On that point, as you all are thinking, like I was talking to Alexis, uh, one of the time, many times we've talked recently and we, she was talking about as an extension agent thinking, if we don't get some rain before long, I'm going to need to start pulling some things together about watering older trees.
00:42:26
Speaker
because you think like an older established tree in general, it's not gonna be as susceptible to the, it's just really hot stuff. It's gonna be more susceptible to, there's not enough water in the soil. What's the, you all kind of followed drought maps about that or is there just kind of a sense of the amount of time or is there physiological things people observe as far as older established trees?
00:42:55
Speaker
Usually I have to look at maps on that because sometimes it's really hard to get a handle on deep moisture that's actually in the soil, available moisture at given depths. So I have to use maps and they tend to be larger geography based maps, but I have to use those and kind of reconcile what I'm seeing based on what I'm seeing on the computer and match the two up to see, you know, if that has anything to do with it. Cause it's really tough. I mean, you have to water pretty deeply. If you're talking about something like a tree,
00:43:25
Speaker
goodness, and that's tough. It's hard to get water down that deep, and it takes a while to do that based on soil composition. So I'm less technical about it, apparently, than Ray is. In general, we use the thumb for majority of our deciduous plants, annual perennials, the one inch of water a week scenario.
00:43:51
Speaker
And that's like one inch per square foot kind of idea. Any unit area. Yeah. And so it can be hard to kind of think of that for a tree. You're like, well, how much water is that actually? So I tend to think if we don't have rain within two weeks and our temperatures are around the 80s,
00:44:11
Speaker
or higher than you need to water. So that's just kind of something that I don't know if I've just grasped from personal as well as book knowledge. Another way to like, if you're like, okay, well, if you're not
00:44:26
Speaker
a general thinker like that. If you can't relatively easy get a, um, like a shovel, like a trowel or a soil, I would say a soil probe, but not everybody has one of those, although you can often borrow those from your local extension office.
00:44:44
Speaker
But a trowel, something like that. If you can't relatively easy get that down into the ground, you know, about eight inches, which is where a lot of our root system that's going to take up water, even trees and those larger perennial plants, eight to 12 inches. If you can't get something relatively easy down in that far, it's probably too dry. Another thing is it could be really compacted and then you're
00:45:08
Speaker
a suffering, you're going to suffer with the same, we've got other problems, but you're suffering with, you're going to suffer drought stress because of that compaction. So either way you need to water. Um, and, and so that's kind of a, that's like a, something you can actually do if you're not like a generalist. Well, it hasn't rained in two weeks. I should probably water type thing. Sometimes just something like a simple. There are some water calculators online, but if you look at a mature tree, let's say a 75 to a hundred year old oak.
00:45:36
Speaker
And somebody says, well, I want to water that. I'm experiencing some stress. I have bacterial leaf scorch. It's going to die in 20 years, but I want to mask those symptoms for the next 10 years. And you go through a thinking process with them. And it's, I mean, it may say five to 8,000 gallons of water on that tree for watering. And then they back up and think they're like, what? But based on the depth and the species of tree and the age of tree, now that's an extreme case. Homeowners, if you're really lucky, if you have a tree that's
00:46:06
Speaker
a maple that's eight to 10 years old, you can do a much better job on that. But mature trees take thousands of gallons of water slowly dripped over time. And it's an expensive endeavor and it's a slow process, the drip line of these trees where the roots tend to be dispersed. It's tough, but on smaller trees like Alexis is saying, it is awesome. You can make some really good headway, especially
00:46:32
Speaker
those plants that have been in the ground three years or less, because I don't know about you guys, but I don't consider a plant established at the bare minimum three to four years in Kentucky. If you have something like, you know, a tree or shrub, I do not consider it established at all until three to four years old. Then you can make some really good gains by watering and doing that intelligently like Lexus kind of outlined there. But older trees are much tougher, thousands of gallons. It is amazing when you actually start calculating how much water these plants take up. It is incredible.
00:47:01
Speaker
on mature trees, but the younger trees, you can do some good, especially those... So bang for... Sorry, go ahead.
00:47:08
Speaker
I was gonna say the best thing you can do for a tree is to mulch it. I was just gonna say the same thing. Absolutely. Don't make a volcano, you fools. Yeah, don't make a mulch volcano. We like mulch donuts. Yeah. Okay, we're donuts. You want a mulch area where it's not where the trunk is, but where the roots are. Because if you put it on, and the reason why, and it's sad, it's just sad when people, when it happens, because people think that they're taking care of, they're thinking they're wrapping their little tree trunk up in a nice little blanket. Tucking it in. And saying, oh, you're gonna like a little hood.
00:47:36
Speaker
the moisture content on the bark can actually cause die back into the tree. It can girdle the tree or significantly damage it to the point where it can't move water and sugars and starches as effectively anymore. And so if you're not, many of you are probably familiar, but if you're not, don't, I'm not one of those people who shames people because again, we're just
00:47:56
Speaker
There's a lot of things I don't know about. We're all just people here. But if you haven't seen that mulch volcano and your family member or friend is doing that, maybe just reach out to him and say, Hey, let's make that a donut. It's really easy. It's real simple. You may have them. Yeah, you'll probably use less mulch in terms of donuts. Yeah. I'll post a picture of mulch volcanoes because I unlike
00:48:21
Speaker
Brett, do shame people, and I take pictures. I don't, I guess I don't shame people. I take pictures, but I don't say where they're from, although sometimes you'll see it, like, you know. It's just a hard thing to see. A particular box store in the background. Yeah. Because people aren't necessarily like, I don't know. They can't, they don't know where it's coming from, from your perspective. Like, hard. Yes. I'm just kidding. I do take pictures though. I do. Because they're great to use. They're good examples. No, no, no. I know you're kidding.
00:48:51
Speaker
I was, that was me experiencing the internal, like there's a, yeah, I've seen them and just like, they're like, it's okay guys. One thing I get the question, you know, we tell people to mulch their trees and they say, okay, well, how much do I mulch the tree? And I go, how much are you willing to mulch the tree?
00:49:06
Speaker
because the limit does not exist. So I say if they want to do it perfectly, they're going to mulch out to the triple line of the tree. So on a 100-year-old oak, that's a big old mulch. And you're not necessarily happy to do it every year. It might be every other year or depending on how thick you lay it down. And the other question is, well, how deep do I go?
00:49:28
Speaker
Ultimately, I would say three, what do you think, Ray? Three inches is a really good depth. Anything more than three to four and the roots get confused, especially when water or people tend to have a tendency to.
00:49:45
Speaker
water too little and they'll sink that. Yeah. Yeah. Three, four. And you're better to, you're better to reapply mulch in a smaller layers rather than try to kind of maintain three to four. Yeah. Yeah. We're going to hook this up and walk away. Things are going well. You can just see the very crown of the tree poking out of the mulch. It's not a volcano. Does a tree come out of that powder mulch? That is a real volcano. Because if things are going well, that mulch is going to disappear because your soil microbes are happy and they're munching and it's going to be
00:50:15
Speaker
Right. Yeah. And if you've got a lot of roots that are up on the surface, this is not drought stress related, but it reminds me if you have a lot of roots that are up on the surface of a tree, it's probably because you have a lot of compaction issues in that soil. And so they're up looking for air. So if you mulch that, that can help with that problem. And then you don't have to mow or be around those exposed roots either. So just a little food for thought. Just remember is like a good kind of way of telling people not to mow up next to the tree.
00:50:43
Speaker
without being judgmental. Oh man, we have this dog that someone just yeeted with a weed eater like 30 years ago or 20 years ago. It was not me. They weeded. Not this time. Two weeks ago, this guy trashed it. I used to strip all my trees down to the cambi until Alexis told me she shamed me. She took a picture of me and posted it on the internet with my name. I took a picture of you and posted it everywhere. Shame on you.
00:51:18
Speaker
All right. Well, we hope that you have kind of collectively understood sort of a few things about heat and drought stress. And so maybe I think sometimes understanding that, yeah, well, I just, I think understanding the mechanisms sometimes is like really helpful for people understanding why, how something works. And like, you're all smart people here, you know, understanding how something works and you can make a lot of inferences for that. But yeah, who wants to recap?
00:51:33
Speaker
I didn't really, but I would.
00:51:45
Speaker
Oh, I mean, I think just the idea that the general plant mechanism for moving water and nutrients through it is that at the leaf surface, this evapotranspiration process happens. There's water getting pulled out the top, kind of like you or me sweating. There's water vapor. There's other things that are leaving the plant that pulls water through the roots. Along with it comes things like nutrients and as well as the
00:52:15
Speaker
Yeah, I think that's all the nutrients of water getting pulled up through the roots. When we have heat, that in some ways can interfere with that process, whether that be by
00:52:29
Speaker
If it's really hot and humid, it slows down the whole process of the water going anywhere because of the concentration difference. If it's just really hot, it could be that the root system isn't big enough to move enough water through it at one time. It could be any number of things and the plant may have some different physiological responses. Many of those are not caused to be shocked or to be afraid like I have been at times in my life, but it may be time to water and think about that. You can do that by paying attention to the
00:52:58
Speaker
The temperature, if it's above 80, 85 or so, that's where your danger zone and our zones at least contend to be. And if you have issues or you have questions, you can always get in contact with your extension office and you can find lots of good resources online. But just keep an eye on things and do your best to learn a little bit more each year. And it's a manageable thing.
00:53:21
Speaker
Inspect your plants. Yeah. No, no, no. Inspect your insects, inspect diseases, inspect for huge trash. No replacement for time to go. Put plants where they are supposed to be. Right, plant, right, plant. How
Conclusion and Call to Action
00:53:30
Speaker
much sun or how little shade? If not, invite a wild geranium to come give it a hug. Yes. Yes. Geranium hugs. That will be our next, next time we do inter, intercropping. I'm going to, interplanting. I'm going to talk about weeds. Plant hugs. They're good. But anyway, so we, I,
00:53:47
Speaker
are thankful that you guys are here. We hope you are enjoying this. If this is a show that you like, we're going to start doing that thing that all the other podcasts do. And we're going to say, Hey, leave us a review because it helps other people find us. So it's not just because I need a little, you know, like
00:54:02
Speaker
extra in a little feather in my cap today. But it does, I'm assuming it has something to do with an algorithm. I don't know. I'm a plant person, but I'm assuming there's an algorithm involved. And so if you're leaving reviews that are, I believe positive, please, hopefully they're positive. Anyways, leave us a review. It helps other people be able to obviously to find us. So we do appreciate that. And you can now, there are,
00:54:31
Speaker
ways to contact us in the show notes that I believe are clickable. If my techies in the room will confirm, yes, I'm getting confirmation head nods, click, click, boom. And so you can contact us there, email. Again, we're on Instagram, a Hort Culture podcast. If you ever have any ideas for things you want to know,
00:54:50
Speaker
definitely give us a heads up. We would love to because we're just coming up with cool stuff as we think about them, as the weather comes with them, as we, I don't know, come up with wild hair ideas. We just, we just like to share that with you also. We hope that as we grow this podcast, you will grow with us and join us next week. We're going to talk about some potted plants, which I'm very excited about. So thank you all so much and have a great day.