Thursday, June 30, 2011

Plants wilting in the middle of the day?

Do your plants wilt during the middle of the day, every day, in the blistering heat of summer?

Do you panic and water them immediately? (Quite a normal reaction.)

Well don't despair. Your mid-day wilty plants may not need water at all. And in fact, if you water them, you may actually may be making the problem worse.

Wilting Hamelia (firebush): notice the curled leaves and droopy flowers

Here's the deal:
First, as a general rule of thumb, plants don't grow when temperatures are above 96 F. (And when was the last time we saw 95 around here?) One reason for this is because plants need water to grow. That's pretty obvious. But did you know that plants can't take up water without losing water? And plants are pretty smart (I have a botany professor that would kill me for anthropomorphizing plants), so they shut down their water loss, thus their water uptake and growth, at times when it would be harmful for them to grow. The process of how water moves into the roots, through the plant and out through the leaves is called transpiration.

So how will you know if your plants are just taking a little siesta or if they truly need water? Watch to see if they straighten up once the sun goes down, or if they've recovered by the next morning. If so, there's a good chance they need lower temperatures and more more moisture in the air, not in the soil.

There's not a whole lot you can do about the temperature, but you can mitigate heat if you establish shade over your plants, which may not be a very real possibility. But if it is, use shade cloth. White shade cloth, which reflects the most light would be good. But black shade cloth would also work well.

As to the moisture in the air, mulching will help. Make sure to have lots of mulch around your plants. Keep the mulch moist by watering the area just enough that the mulch gets wet without over watering the soil beneath it. Wetting the mulch daily, or even twice a day, may help your plants. But they still may also wilt. Either way, the moisture in the air around the plants helps to limit water loss, which will help relieve some of the heat stress.

But one thing you don't want to do is keep the soil completely drenched at all times. This sets up a situation where the roots are damaged due to the lack of oxygen, and to the possibility of disease.

Check out this video of a segment, Why Plants Suddenly Fall Over, that I did on Central Texas Gardener, which addresses this question from one of our viewers.

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