Heat's Effects on Growing Vegetables

Wilting

• Plants exposed to heat quickly lose water as their leaves release water vapor to keep cool. Most vegetables lose water rapidly above 90 degrees Fahrenheit, and they will begin to wilt unless they are irrigated regularly. Internal water pressure helps maintain the rigidity of the cell walls of each plant cell. When your vegetables are dehydrated, the cell walls contract; the entire plant droops. Dehydration that lasts less than a day may not permanently damage plants, even if they are noticeably wilted. Plants allowed to dehydrate repeatedly in hot weather often grow poorly.

Growth Problems

• As the temperature of your vegetable plants exceeds 94 degrees Fahrenheit, photosynthesis decreases rapidly. This can severely limit the growth of your vegetables, especially if you are growing fruiting vegetables. Night temperatures above 94 degrees limit the amount of sugar and nutrients your fruiting vegetables can devote to producing fruit.

Tissue Damage

• At temperatures above 115 degrees Fahrenheit, the plant tissues in your vegetables begin to die. In most cases, the temperature of your plants is close to the air temperature around the plant. Under certain circumstances, the temperature of your vegetable plants can be significantly higher or lower than the surrounding air. Well-hydrated plants can cool themselves by releasing water vapor through their leaves, and are more likely to survive high temperatures undamaged.

Wind

• Strong winds during warm weather can worsen heat damage to your vegetables. Mild winds can help cool the plants, but at the cost of increased water loss through the plants' leaves. Strong winds combined with high temperatures can dehydrate your vegetable plants beyond the ability of their roots to draw water from the soil. Under hot, windy conditions, your vegetables can suffer heat damage because they are unable to shed heat fast enough.

Preventing Heat Stress

• High temperatures cause water to quickly evaporate from the soil around your vegetables. Mulch applied to the soil around your vegetables reduces evaporation of soil moisture. Avoid using dark-colored mulches; they absorb more heat than lighter mulches and increase moisture loss through the leaves.