By Andrew Holsinger
It’s that time of year when shade trees show their greatest benefit to homeowners. Shade trees provide shelter from the sun and can help contend with the energy costs of cooling our homes during the summer.
While much of the focus tends to be on the upper canopy during the summer, the root system and trunk of the tree should not be neglected for attention. Signs of stress may be noted in the canopy when not enough moisture has been received as “leaf scorch” develops. Leaf scorch can be an indicator of the water supply of the tree, but damage to the root system or trunk can quickly reduce the amount of moisture transported through the vascular system under the bark.
Damage to trees can be avoided by carefully planning their placement to avoid injuring the root system by future digging nearby. Common sources of injury can be from string trimmers or mowing. Be aware that some trees (especially maples) are shallow rooted and may be prone to injury from mower blades. Mulch around the tree can help to prevent damage and conserve moisture through these hot, summer months. This also provides some distance from the trunk for the mowers and string trimmers to avoid damaging the tree. Mulch should not be applied directly against the trunk of the tree and only to a depth of 2 to 4 inches.
Sometimes mulch isn’t enough to preserve the moisture as not enough rainfall is provided. Even large established trees can benefit from irrigation as more water is lost from a mature tree than compared to a younger tree. If not enough moisture is transported from the roots to the canopy, leaves turn brown there may be die back of twigs and branches. Watering can be accomplished with a sprinkler or to deliver a targeted amount of water to the tree’s root zone a slow dripping hose can be used when no rain is predicted for several days.
Broadleaf trees are primarily thought of when it comes to shade, but evergreens do have the capacity to provide some shade in the summer and are the most susceptible to drought-related problems. Prioritize to irrigate evergreens first when water comes in short supply.
Remember to water in the fall when conditions are dry. Measuring the amount of water applied with shallow pans can be contrasted with the amount absorbed in the soil. Use a sharp spade or shovel to dig into to soil to a depth of 6 to 9 inches to ensure adequate watering is being accomplished.
Enjoy the shade and keep your trees healthy throughout the seasons by scouting for signs of stress which can encourage insects and disease.
Andrew Holsinger is a University of Illinois Extension horticulture educator.