Heat Stress – Protecting Gardens and Gardeners

By Ann Barnes, EMGV

It’s hot out there! Every summer, stretches of humid 90°+ days leave plants and their gardeners feeling thirsty and wilted.

Plants lose water through leaves and must take up water from the soil to replenish what was lost. If there isn’t enough moisture in the soil, or if it is hot enough that the plant can’t replace lost water fast enough, the plant will wilt. Often, plants wilt during the heat of the day but recover when temperatures cool in the evening. (Look for more about wilting in a later blog post).


This hydrangea’s roots are unable to take up enough water to keep the plant from wilting during the day. The plant recovered by evening.  – photo: Ann Barnes

Wilting is not the only hot weather challenge plants face. Cool season turfgrass such as fescue can become dormant when temperatures are in the 90s and may begin yellowing. Flowering plants may have smaller blooms or may flower for a shorter time. Tomatoes and other garden staples do not set fruit well when temperatures are high for extended periods. Some trees begin to show fall colors or drop leaves. Scorch, the browning of edges of leaves throughout the plant, is another condition brought on by heat stress. Gardeners can give their plants an advantage by using good watering practices.

To help your garden make it through a heat wave, make sure plants have enough water. One inch per week (including rainfall) is recommended.  Plants in containers, new plants, and those in particularly hot, sunny places may require more. Watering in the morning is ideal so that plants have a supply of water before midday heat arrives. If early morning isn’t possible, be sure to water early enough that leaves can dry before the sun sets to reduce chances for fungal diseases. There is no need to water daily – watering deeply a few times a week is better for plants because it encourages deeper root growth. Overwatering causes its own set of problems, so check your soil to make sure your garden isn’t already moist enough before you start moving hoses and sprinklers.

In addition to watering properly, mulching will help plants beat the heat. Mulch holds moisture and acts as insulation, keeping the soil cooler. Mulch also helps to keep weeds down. Weeds compete with garden plants for water and nutrients, so removing or preventing weeds will keep them from taking precious moisture from your plants.

Gardeners can also suffer from excessive heat. Be sure to water, weed, mow, and perform other garden chores early in the day whenever possible. Drink plenty of water and take extra rest breaks indoors or in shade. Know the signs of heatstroke and heat exhaustion and seek medical attention if necessary.