Plants and Trees Are Suffering From The Heat

Estimated read time: 3-4 minutes

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It is too darn hot! Few gardeners would disagree and if trees could vote they also would cast an affirmative vote. Most of us are looking for shade or air conditioning to help us beat the heat. Plants have no such options and many are suffering from the heat.

Since the first part of May, trees have had frosts and within a few weeks were subjected to record heat. Our humidity is sometimes drier than the Sahara desert and then mix in the hot south winds, and it is easy to understand why many trees are under stress.

Most plants grow best in a temperature range of 65-85oF. Outside this range, systems slow down to protect the plants and help them survive extended periods of hot, dry weather.

Plants do not manufacture as much food when temperatures get too warm so your garden does not grow as well. Warm season plants operate at slightly higher temperatures, but even those shut down when temperatures get too hot.

Temperature stress in plants takes many forms. Among the most common is a condition called summer leaf scorch. This is not a disease but it is the symptom of the disease. The direct stresses from heat are drying out and scorching from burning and lack of water.

Large trees are usually most affected by the hot, dry weather and summer leaf scorch is common on trees with large, broad leaves. Problems show frequently on poplars, maples, horse chestnut, and catalpas, although all species can be damaged.

The leaves on scorched plants are usually dried up around the edges. As the problem gets worse, the entire leaf might die. Leaf scorch is aggravated by poor quality irrigation water and poor quality soils.

Sometimes plants are scorched because the water cannot move fast enough from the roots to the leaves. This frequently happens when hot, dry south winds dry the plants like a proverbial blowtorch in spite of the moisture in the soil.

In many cases, soil moisture is adequate, but the tree cannot move water from the soil to the top of the tree fast enough to prevent scorch. It is usually worse on trees with pavement around them as this restricts the roots and their ability to absorb water. Water trees deeply every two to three weeks so the moisture penetrates two feet into the soil.

When plants cannot move enough water from the soil to the leaves, the leaves scorch or wilt. If it continues to happen, the tree will lose its leaves and can eventually die. Most people understand that if the soil is too dry, the leaves will wilt and scorch. The problem is harder to diagnose if the soil is moist or even soggy wet.

One of nature's strange ironies is that trees that are dying from lack of water show the same symptoms as those that are dying from too much water. The reason is simple. In both cases the water is not reaching the leaves. Too little water and there is none to reach the leaves. Too much water and the small absorbing roots that take the water in are destroyed and cannot move water to the leaves.

These tiny roots can only survive if there is oxygen available for respiration. Waterlogged soils exclude the oxygen and the roots die. Consequently not enough moisture is absorbed and the leaves have the same scorched symptoms that they get with severe drought injury. The same problem happens when trees grow in compacted soils.