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Index : Watering
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- 24. Spray Plant Leaves Too Keep Them Cool - Top
One of the best ways to cool down heat stressed plants is to give them a mid-day shower with cooling water. At this time of year, the monsoon rains provide this same cooling effect, and plants love it! But the rains aren't dependable, and some plants, especially new ones, can use some relief.
If you notice plants wilting in the middle of the day, shower them down with cool water. A watering-wand or hose-end sprayer with a gentle shower setting works best. You don't want a narrow blast of water, but rather a wide, gentle stream that will quickly wet the leaves.
Garden hose laying out in the sun will be very hot. Before you spray water on your plants, run the hot water out of the hose on an open patch or bare soil or rock mulch away from other plants. Wait until you feel cool water coming out of the hose end before showering off your plants. Never apply hot water on your plants.
In the summer, water coming out of the hose bib will be about 80 degrees. This is cool enough to significantly reduce the 100+ leaf temperature of heat-stressed plants, but not so cool as to shock them. Contrary to the opinions of some, applying water to plant leaves in the full, mid-day sun will not burn the leaves! The water droplets, as some people believe, do not concentrate sunlight to create a burning effect. Try it and you'll see. I have been using this method to cool plants for years and have yet to burn even the most delicate of plants.
Allow the water to run over the leaves for a minute or two. This will effectively dissipate the heat and, at the same time, moisten the soil under the plant. The top layer of soil is the first to dry out, so wetting the surface will provide some additional moisture for the roots while increasing the humidity around the plant.
Small plants with poorly developed root systems are most likely to need a cooling shower. This includes various herbaceous plants such as flowers, vegetables and herbs. Also recently planted trees, shrubs, vines and ground covers will benefit from a shower, even if they are not showing signs of wilt. These plants have yet to develop an extensive root system and are thus less capable of absorbing adequate supplies of water.
Plants that have been revived with a cooling shower during mid-day may be wilted again by evening. Don't wait until morning to water these stressed plants. Apply a generous amount of water in the early evening to help them recover overnight.
Some gardeners worry about the salt content of our water, and it's potential to burn leaves. This is also not a problem. Tap water in Tucson and surrounding communities is a good quality and is very low in salts; only about 300 parts per million (ppm). At this level, you could spray plant leaves several times each day, for months on end, without damaging the leaves or the plant, even the most delicate ones! To damage even highly salt-sensitive plants, the salt content would have to be well over 1,000 ppm. In fact, the only instances I have seen of plants injured by spraying leaves (weeks on end), is when salt levels exceeded 5,000 ppm!
Another method to reduce heat-stress on plants is to provide them shade. This can be done by placing an overhead cover of shade cloth attached to stakes or a simple frame made of stakes or 1 x 2 inch lumber pieces. Shade cloth can be purchased at most garden centers and home supply stores. You can use shading in conjunction with cooling showers to provide the greatest relief for plants.
Finally, never prune over-heated plants! Pruning will inhibit the growth of roots by reducing the number of leaves that manufacture the food necessary to grow new roots. Developing new roots that will increase the water supply to the leaves is the only long-term solution to wilted, heat-stressed plants.
Applications are still being accepted for the Master Gardener training program. For information about the program and an application form, phone the Pima County Extension Office at 626-5161. Green Valley residents interested in the Master Gardener program may call 648-0808 for information.
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona,
520-626-5161. - Updated: August 5, 2001
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