Supplemental Watering, Mulch Can Alleviate Drought Stress

Extended periods of hot, dry weather and subsequent years of seasonal drought causes stress in both mature and newly-planted trees. Dry soil may cause tree roots to die, reducing the tree’s ability to absorb water when it finally rains. Drought-stressed trees are also more susceptible to insects and diseases.

Don’t wait until you see non-uniform wilting and yellowing of leaves, premature leaf drop, dieback and/ or tree death.

Provide supplemental watering during the hottest and driest times of the year, guided by these tips from the City’s consulting arborists:

• Before watering, test soil. Stick a long (8”+) screwdriver into the ground near the outer edge of the tree’s canopy. If it comes up with little to no soil stuck to it, the soil is dry.
• An infrequent, slow and deep soak beats watering a little every day. A slow, deep soak promotes deeper root growth and overall health by ensuring that roots receive water. Place a soaker hose under the tree’s canopy in a spiral or zig-zag arrangement. Applying water directly minimizes water loss due to evaporation. Avoid watering at the base of the trunk.
• Turn the soaker hose on in the evening, or early morning, and leave it on for at least one hour. Mature trees may need to be soaked for several hours (depending on the soaker hose and water pressures), but be cautious, as over watering can be equally detrimental. Check soil periodically to make sure the water flow is slow and deeply penetrating the soil.
• No soaker hose? Drill three 3/16- inch holes into the bottom of a 5-gallon bucket. For younger trees, place the bucket beneath the tree’s canopy (close to the trunk, but not right up against it). Fill the bucket for a slow, deep soak during the hottest and driest times of the year. One 5-gallon bucket will need to be refilled three to 10 times to fully water a tree, depending on the tree’s size. Move the bucket each time you refill it. Repeat the process monthly when soil is dry, and more often for young trees.
• Set a calendar reminder sometime near the last week in July and the last week in August to remember to check the soil. When the soil is dry, a slow, deep watering is needed once a week for young trees and about once a month for mature trees.
• Maintain a grass-free mulch ring around your trees. A 2- to 4-inch layer of bark mulch helps to retain soil moisture and moderate soil temperature. Avoid piling mulch against the trunk around the base of the tree and don’t exceed the recommended depth.