What Can Help Plants Survive High Outdoor Temperatures?

Take precautions to help your plants beat the heat.

It's becoming an all-too-frequent problem for gardeners: extreme rises in temperature that can devastate a flourishing garden in a matter of days -- even less for some exotic or delicate plants. Even a short-term heat wave can cause unprotected plants to wither, cease blooming or fruiting and, in the worst cases, die. There are some simple precautions you can take, however, that will keep your whole garden fresh and resilient.

Proper Watering

The first step in battling the effects of a heat wave in the garden is to employ the correct watering techniques. Water early in the morning (before sunrise) so that the water has chance to seep into the ground before the sun can evaporate it. Water deeply until the soil is saturated at the root level and preferably using drip irrigation or soaker hoses rather than overhead sprinklers. Be sure to pay special attention to container plants, which will dry out faster than plants in the ground and will likely require more frequent watering.

Plant Selection and Zoning

Your garden will have an edge in standing up to extreme heat if you've planted the right plants in the place. Drought-tolerant plants, including native plants and Mediterranean plants, have low-water requirements and, once established, tend to fare better in higher temperatures. It's also helpful to group plants in zones by their water needs so that the regions of your garden with the most drought-tolerant plants can go longer between watering.

Heat Barriers

Putting something between the sun and your plants can mean the difference between a plant that lives and a plant that dies. Spreading a 3- to 4-inch layer of mulch around the base of your plants will hold more moisture in the ground to keep roots hydrated. And for really delicate plants, you can erect a temporary tent of remay cloth, a spunbonded polyester fabric that is used for floating row covers or frost or shade protection.

Avoiding Additional Stress

Most importantly, you should avoid adding more stress to your plants during a heat wave. That means no pruning, transplanting or fertilizing until the temperatures have returned to normal and your plants have fully recovered from any negative effects of the heat. With such precautions and a little time to adjust, your garden will not only survive but thrive through the hottest of seasons.

Treat Plants & Trees Suffering from Heat Stress

Heat stress is a serious problem for trees and other plants when the temperatures are high. Plants that are already compromised due to low nutrition in the soil or that have disease around their roots will not fare well and can die from heat stress.

All plants require a given amount of micronutrients, water and sunlight to properly perform photosynthesis, the process that creates the sugars (called brix) that the plants survive on.

When the temperature is high, several conditions can manifest themselves in the plant's ecosphere. If there is too much rain, fungi can take over and cause diseases to hinder plant growth. If there too little rain, the plant can't create sugars that are needed for growth, and so they are stunted. As a result, plants under these conditions will either not produce fruits or flowers, or they may produce fruits and flowers that are blighted.

Signs of heat stress are irregular yellowing and dropping of leaves that may have rust-colored spots or bumps. The specific causes of these symptoms include nitrogen deficiency (browning from the leaf tip inward) and potassium deficiency (browning along the outer edges). Brown spots and bumps are frequently attributed to a bacterial condition coming out from the soil. 

Treatment of heat stress needs to be proactive to be most beneficial. Treating plants with a biostimulant containing sugar, such as MaxGrow, and a program of regular watering is the best way to prevent or treat heat stress.