Garden Tips Newsletter
Wilting (Plant, Man and Beast)
June 22, 2009
Recent temperatures in the triple digits can cause wilting of plants, man and beast. Animals can get to a cool spot in the shade. We can go indoors, cool off and get a big glass of water. Not so, with our poor plants. They are stuck right where they are. As gardeners, we are well aware of the many effects of extreme heat on our plants.
We all know that high temperatures can delete soil moisture resulting in wilting of the plant. Limp or drooping leaves are a sign of plant stress. Most of the time drooping leaves indicate lack of water. Usually we can water well and the plant will recover. But if allowed to get too dry, the leaves will fall off. Before you give the plant up for dead, water and wait a couple of weeks to see if it will sprout new growth. If so, cut away the dead foliage and stems, and feed with a half-strength solution of 20-20-20.
Wilting or drooping of plant foliage can also be an indicator of other stressful situations. Anyone that has ever grown squash, gourds, and pumpkins know that during the hottest part of a sunny day the large leaves of these plants will droop—even sometimes when the soil is relatively moist. I have a Chinese parasol tree that has huge leaves which tend to droop when the temperatures get high on a sunny day even if the soil has some moisture. What’s with that? Well, if the plant is otherwise healthy, and the soil is moist, the drooping leaves of some plants in this situation can be a natural response to decrease the plant surface area exposed to the sun. This lessens the rate of transpiration or loss of water vapor from these huge leaf surfaces, thereby conserving available moisture. In other words, it’s like you or your dog getting in the shade to decrease the amount of water loss by sweating (you) and panting (your dog). Plants are pretty smart!
There is another reason a plant may wilt. If you have checked the soil around the wilted plant and it is plenty wet, the drooping foliage is probably an indicator of the dreaded rot root. This happens when the plant has been overwatered to the point that the roots have begun to rot due to the invasion of any number of disease pathogens. This situation can be made worse by less observant gardeners who continue to add water to this wilted plant thinking the drooping leaves indicates a lack of water. Waterlogged soils literally suffocate roots resulting in root death which in turn prevents top growth from getting the water and nutrients it needs. The plant is starving to death for water in a water logged soil because it doesn’t have adequate roots for uptake. Keeping container plants in a saucer of water may result in this type of wilting due to root suffocation and death. I have had the drain hole in container plants get plugged and after mindlessly watering the plant to the point of death finally figured out what was wrong. You should be more observant than that! If you catch the situation early, you may be able to save the plant. If it is in a pot, allow the soil to drain off excess water and move to a place out of the sun. If a plant has been over watered out in the garden, it probably is in the wrong place and water pools there after a rain, rather than you irrigating excessively. The best thing to save the plant is to dig it up, if possible, and move it to a well-drained area of the garden. Replace with a plant that likes wet soil like cannas, elephant ears, amsonia, sweet flag, sweet shrub, Virginia sweetspire, or osmanthus.
There are other reasons that plants wilt, for example, due to voles eating all the roots off or it could be due to other factors like disease or insect damage. In most cases wilting is due to the three reasons above with the most likely being lack of water. So, don’t forget about your poor plants stuck out in the high temperatures and hot sun probably dying of thirst, as you and your dog are lolling about in the shade!
Lelia Scott Kelly, Ph.D., writes Garden Tips weekly and is a Horticulture Specialist with the Mississippi State University Extension Service. Her office is in the North Mississippi Research & Extension Center, Verona.