Rehydrating Wilted Leaves

maplerbirch(4)August 8, 2012

An internet aquaintaince made a comment that, plants bouncing back after wilting in the hot sun indicates, that there is sufficient soil moisture present. It's just that the roots are unable to keep up with the heavy demand placed on them during that period. We all know the example of Hydrangeas wilting in the afternoon, but they are just fine by evening.

This year it seems there's stress on everything in the garden and I have been misting the wilted foliage, with a water hose until turgor is restored.

I wonder if this practice is helping develop a better root system, because the leaves will have the energy to continue its job as the food producer.

What does everyone here think about that idea? Does it make sense or not? :)

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Tiffany, purpleinopp GardenWeb, Z8b Opp, AL(8B AL)

With the heat here, there are a lot of plants in my yard that wilt every afternoon and they are doing well, growing. I would be afraid of encouraging molds and mildews by wetting leaves in high heat. If a plant has the ability to wilt on a hot afternoon, that's a survival mechanism that can't really be improved. If you have recently planted something new, a bit of shade for hot afternoons is the best thing I know. Check in the morning to make sure it's turgid, then let it do its' thing.

    Bookmark   August 8, 2012 at 9:28AM
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I agree, but was thinking more about the plants thriving, instead of just surviving. thanks for the response. :)

    Bookmark   August 9, 2012 at 9:45AM
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rhizo_1 (North AL) zone 7

Misting will cool the foliage temperarily, perhaps causing stomata to open and photoevaporation to begin at a time that is disadventageous time for the plant. That, it seems to me, would cause more stress on a plant in the long run by short circuiting its natural preservation systems already in place.

Plants wilt because they cannot access enough available water fast enough. Stomata shut down and if the plant wilts, there will be less surface area exposed to the sun. That's a good thing.

But available soil moisture evaporates from the soil surface and photoevaporates from leaf surfaces. Once soil moisture turns hygroscopic, the plant has been struggling for too long.

    Bookmark   August 9, 2012 at 4:18PM
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I understand what you are saying: "Misting will cool the foliage temperarily, perhaps causing stomata to open and photoevaporation to begin at a time that is disadventageous time for the plant"
Perhaps I should mention that I continue irrigating the plant during the course of the day, so it isn't temporary. By the time the cool of the evening came, the soil, roots, stems and leaves were fully hydrated.
Yet by sundown all surfaces were usually dry

Of course I can't make that claim for the huge trees, wilting by late afternoon. I have no idea how much water is needed to fully hydrate those guys. I generally soak down the branches and the trunk along with spraying the leaves, so some roots are getting water.
Thanks for your thoughts on the matter. It gives me more to think about when I find meaning in my observations. :)

    Bookmark   August 10, 2012 at 7:38AM
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Some research indicates that misting can lower the temperature around the plant which then decreases the plants need to respirate moisture to cool its environment which then helps slow wilting, in greenhouses. There did not appear to be an increase in plant diseases because of that misting.
Plants can wilt when the loss of moisture excedes the ability of the roots to supply adequate levels of water to the leaves, but that can also happen if the soil is too wet and the roots do not have the air they need to get the moisture from the soil. Too much soil moisture is as bad as too little.

    Bookmark   August 11, 2012 at 6:38AM
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Thanks kimmsr, I like what you said about: "Too much soil moisture is as bad as too little".

That problem has popped up with several friends watering their gardens this year. They are so afraid of the heat, sun and drought that their soils can't breathe at all. That is a very important point. :)

    Bookmark   August 11, 2012 at 9:27AM
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I've showered my garden many times in the afternoon heat to revive the plants from wilting.

Once read that it actually cuts down on disease as spores/fungus start growing in the heat and then dry out and die. This has been my observation, plants with afternoon overhead watering don't seem to develop any diseases. Just need to make sure they are dry before sun goes down.

Since my garden only gets afternoon sun, preventing wilting is necessary, otherwise the plants would never get any photosynthesis time. Having a woodchip mulch along with with overhead (not just drip) watering has helped considerably. The wood chips absorb water and encourage lateral feeder roots to develop. These lateral roots get a good mixture of water and oxygen to provide the plant during heat spells. If I rely on just drip irrigation the plants wilt no matter how wet the soil is, because there are no "top of the soil" lateral roots to provide the extra moisture uptake needed in heat.

    Bookmark   August 12, 2012 at 4:34PM
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rhizo_1 (North AL) zone 7

Em, I may be misinterpreting your post, so please forgive me. The information about mulch, feeder roots, and watering seems off target.

A layer of mulch IS hugely beneficial for our plants and for the soil system. But it is essential that watering be sufficient to get through the mulch and into the soil. Merely moistening the mulch will encourage the shallow, fibrous root system to grow into the mulch....a very troublesome situation.

The fibrous root system of trees will always, by their very nature, be located in the upper root zone. But it is hazardous to trees to encourage the non woody (feeder roots) to enter the mulch.

It is always, always a good idea to water deeply but less frequently. As far as hosing plants down to 'cool ' them....that's up to each of us. It is important to know, however, which diseases might be prevalent in your location. Most fungal disorders require water in order to infect, grow, and spread. Powdery mildew is the one that I am familiar with which is controlled by rinsing the foliage frequently.

I do agree with you that problems associated with afternoon or evening watering are hugely exaggerated. My preferred time of day to water is in the evening....even after dark. I do not use a drip system.

    Bookmark   August 13, 2012 at 7:51AM
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Those were the lines of thought I was moving along, emgardner. I'd often thought of washing the leaves of it's dust was an added bonus. You made an important point about the plant's ability to photosynthesize during the time it's normally wilted.
I really struggle with finding plants I like, that will fit the garden scheme, and will do just fine with afternoon only, sun. I appreciate your response. :)

    Bookmark   August 13, 2012 at 8:29AM
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Thanks for your courteous reply. I agree with your statements. Especially important for trees to have deep watering. My fruit trees only get deep drip watering.

My comments where based on my vegetable garden experience. While I use drip also in the vegetable garden, I could not get a response with just drip (except pole beans).
When I added surface shower watering the plants did much better. They all are just one season vegetable plants.


    Bookmark   August 16, 2012 at 12:07AM
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