Re: how to prevent leaves from wilting

Pumkinguy ...

Thanks for that response!    I tried to pack what you said into some rules
of thumb .. can you tell me if I got it right?

To lower temperature when the sun is intense, use a shade.
To lower temperature, use evaporative cooling (mist the plant).
To keep leaves from wilting, lower temperature if the temperature is to high.
To keep leaves from wilting,  add water if the soil is too dry.

Suppose the plant had plenty of water, and the temperature in the patch was
reasonable, but the sun was Texas-style intense... meaning there was more
light than the plant could use.  Are those conditions harmful?  I'm
thinking the shade is really about controlling temperature, not light.

Maybe I can test that with a question:  Chris Andersen, are you out there?
Moraga is about an hour from the San Francisco peninsula where I live, but
your microclimate  gets much more intense sun - I can imagine you maxed out
on usable light.  I know you did alot of misting for temperature control,
but did you need a shade?   Did your well-watered, recently misted plants
ever droop from too much sun?

	Dan Shapiro

>Dan,
>   There is a light compensation point for every plant ( I don't know what it
>is for an Atlantic Giant). Light levels above a certain amount of illumination
>produces no more photosynthetic response, so if you constructed a partial
>shading lattice that produced shade and cooling but still allowed the optimum
>amount of light...you would be gaining. When a leaf is totally wilted for
>whatever reason, photosynthesis is not taking place or is taking place at a
>reduced rate. The flip side of the coin is........lets say that you have a
>lattice set up and it is optimum on a bright sunny day, what happens on a
>cloudy or partly cloudy day. Levels will be lower than optimum. Heat causes
>wilting even when adequate moisture is in the soil. You could have rain all
>night and follow it with a 100 degree day and the plants will wilt. The other
>bad thing with temperature is increased respiration and photorespiration in
>the plant. Respiration and photorespiration(during the day) is the calorie
>burning process in a plant. For every 10 degree C increase in temperature,
>respiration rates double (roughly). So the hotter it is, the more food the
>plant consumes just to sustain itself. Food is made by the plant during the
>day and is consumed by the plant both day and night. Net photosynthate (food)
>gains would be the amount made during the day minus what is used up during the
>day minus what is used up during the night. If your plant is shaded to the
>point where you only get 80% of the photosynthesis and then the plant is
>burning calories rapidly because it is 95 degrees in the shade....you get less
>of a net food gain. Don't forget also that the plant burns calories faster on
>a hot night. For the southern growers, pulling a shade cloth over your plant
>will increase temps on a sunny day so that is not the answer. If you have
>partial shade that is up, off the plant with air circulation under it, you
>will be better. Intermittent water sprays are great for the plant. Evaporative
>cooling takes place and the wilt will stop. You must allow enough time in
>between sprays for the plant to dry out so disease is not a problem. You may
>be able to construct a lattice high enough so the sun hits the plant in early
>morning and late afternoon when things are cooler. Just have the shading in
>the Maximum heat of the day when the sun is overhead. Where I am in
>Connecticut it is hot with no lake effect cooling and too far from the ocean.
>But I am not as hot as Atlanta or Texas. I use overhead spraying and the
>plants don't wilt. My nights are still a little too warm but I don't want to
>water all night, every night for possible disease problems. A 400 pound
>pumpkin in Texas might be a greater accomplishment than a 700 pounder up
>North.
>                                        pumkinguy@aol.com
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