How To Protect Your Trees In Hot Weather

Things are certainly heating up in the CDA area in these recent summer months. An unexpected heat wave can come at any time. Here in the Inland Northwest, where we are used to rain and overcast conditions, high heat conditions can catch you by surprise.

Hot weather can affect even the most well established trees and shrubbery. While summer weather is, of course, completely out of your control, you can help your trees by knowing the signs of stress caused by the heat and how to respond.

Signs Of Heat Stress On Your Trees

Most plants begin to slow their growth when temperatures begin to rise over 90F for a sustained period of time. If it’s been hot in your area for a few weeks or more, you may begin to observe the effects of heat stress on your plants. If the temperature climbs above 104F, you almost certainly know that your plants are feeling it!

A heat wave is described as abnormally hot weather that is sustained for several days. Unfortunately, heat waves are also accompanied by a lack of rain. The combination of high temperatures and drought conditions can be tough on plants and may be manifested in symptoms that are observable in your garden and across the landscape.

When it’s hot outside and you haven’t had enough water to drink, you might get heat stroke. Plants tend to struggle the same way!

If you notice any of these signs around the same time as a heat wave you should be considering heat stress as the culprit:

  • Dropped fruit or blossoms: When the heat is high, many plants will abandon their fruit or flowers in an effort to conserve precious resources.
  • Slowed growth: Trees experiencing heat stress may slow down their growth, or even stop growing all together.
  • Dead or falling leaves
  • Wilting: This may present as rolling or cupping of the leaves.
  • Scorched leaves: Leaves may appear dried up, brown, and brittle.
  • Oozing Sap: You may notice this primarily on the south/southwest side of the trunk where the sunlight is the most direct.

Can Heat Stress Cause Long Term Damage?

Some types of trees are more resilient than others. Certain tree species handle high heat conditions very well, others not at all. One thing is for certain: long term exposure to heat can weaken a tree leaving it vulnerable to new issues or exacerbate existing problems.

In drought conditions a tree under stress will eventually reach a tipping point. Eventually, the tree won’t be able to absorb enough water from the soil to keep all the leaves in its canopy green and healthy. In an effort to conserve water and reduce evaporation, the tree will begin to close the pores on its leaves, called stomata. This will consequently reduce the energy output of photosynthesis resulting in slowed growth. The tree will then be more vulnerable to pests and disease, and may even die altogether.

What To Do When A Heat Wave Strikes

If sustained hot weather is in the forecast, you will want to take some immediate action to protect your plants from the effects of heat stress.

  • Water the roots of your trees. By applying water directly to the soil you can make sure water is getting directly to the roots rather than being lost to evaporation.
  • Evaluate your irrigation system, if you have one. Make sure that the water output is optimum and getting to the right places. 
  • Give your trees a good soak once per week. Watering deeply on a weekly basis is more effective than giving just a little water every day. Be sure to allow the soil to drain well before successive waterings.
  • Consider the differing hydration needs for your varied plant life. In general, newly planted or younger trees need more water than well established ones in order to develop a healthy root system.
  • Apply fresh mulch to the area around your trees’ roots. 2-3 inches of mulch can help to keep roots insulated from extreme heat and lock in precious moisture. Don’t allow mulch to come in direct contact with the trees’ truck – this can lead to mold or fungus.