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Article published Jul 14, 2013
The heat’s on for plants
ROOTS OF WISDOM PAUL ROGERSPaul Rogers ROOTS OF WISDOM
It is not enough for us to cope with high temperatures, but we need to be concerned with the effects that extreme heat has on our animals and our plants.
Normally, July and August are the two months that provide us with our highest temperature. A number of factors are involved, including the build-up of heat on all surfaces and, in general, higher night temperatures, which raise the 24-hour accumulation of heat each day.
During July, sunlight hours remain above 14-1/2 long, and in August, there is sunshine more than 13 hours daily. Some weathermen are forecasting that three of the next four months will average above normal in temperature.
Temperature is one of the critical environmental factors in plant development. (The others are light, moisture and nutrition.) Normally, we concern ourselves with minimum, optimum and maximum temperatures, as each range exerts influences on plants. However, our understanding of what happens at minimum temperatures (plants donít grow or they may freeze) or at optimum levels (plant growth maximizes), but we know appallingly little as to the effect on plants when temperatures exceed maximum degrees.
In general, it is understood that plants differ in what each considers its maximum temperatures. For lettuce, celery and spinach, 75 degrees is maximum, whereas, muskmelon, okra and sweet corn accept higher temperatures as their maximum.
However, a constant supply of available water is critical at high temperatures. Each of the plants growing in your yard has a different maximum temperature that is generally considered to be 86 degrees. (Note that the preferred maximum for northern lawn grasses is 10 degrees lower.)
Homeowners have no control over the weather, but we can lessen the heat stresses that plants are experiencing. Several steps can be taken to reduce the effects of heat. The first is to be aware of the signs of heat stress on individual plants. A plant may wilt, even in moist soil, as a plant is losing moisture more rapidly than it can move moisture from the soil to the plant.
Prolonged stress will cause leaf fall and can cause tissue damage, including death. Trees will drop leaves in an attempt to conserve water. Many vegetable and flower crops will drop their blossoms ó squash, peppers, tomatoes, cucumbers, pumpkins, and beans.
Cold-weather crops such as lettuce and broccoli will bolt into bloom, thus ending their vegetative cycle. Plants stressed by heat will be subjected to increased attack by insects and diseases.
To counteract heat stress, moisture and shade help. Keep the soil moist. Shade the soil with mulch. Shade plants with Reemay or similar shade cloth. Avoid the use of pesticides on stressed plants. Light applications of manure or compost teas or liquid fertilizer may help.
Understand that observing and coping with the effects of heat stress on plants is an opportunity for us to become better, more aware gardeners. As the world warms, we need to be ready.
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