The weather forecast is calling for long-term higher temperatures around much of the state right now. Whether walking, picnicking or parking the car, most of us are seeking the shelter of trees for the welcome shade they provide.
Summer temps can be hard on trees, especially landscape trees in our urban areas. Signs of tree stress caused by lack of water — including dead leaves and leaf wilt — are already observable in many Oregon communities.
When trees aren't well-watered, prolonged drought eventually makes them more susceptible to problems caused by insect and disease — and consequently, a shorter life span.
Here are a few tips for keeping your trees healthy despite the heat.
Symptoms of drought
One of the first signs that a deciduous tree (a tree that loses its leaves in the winter) needs water is that its leaves begin to look dull and limp. More advanced symptoms of needing water are browning of leaves, wilting, and curling at the edges.
Leaves on under-watered trees may also appear smaller than usual, drop prematurely or turn yellow, brown or burned-looking, but remain on the tree.
The situation is similar for conifers (also called "evergreens"); when water-stressed, their needles often turn yellow, red, purple or brown.
Water the trees, not the lawn…and water deeply
Given their community benefits, longevity and contributions to the environment, your trees deserve much higher watering priority than lawns.
However, if trees are only provided with shallow water every day, they're probably only getting a fraction of what they need. Watering trees for short periods of time encourages shallow rooting, which can lead to future health problems for the tree.
When you're deep-watering your trees during the hot months of summer, saturate the soil within the drip line — that's the circle that could be drawn on the soil around the tree directly under the tips of its outermost branches.
Using a regular hose or a soaker hose, water deeply and slowly — slowly is important, so the water doesn't run off. To make sure it gets enough water, keep moving the hose around different areas under the tree.
For conifers, water 3 to 5 feet beyond the drip line on all sides of the tree. Also, if you have a choice, water trees during the cooler part of the day.
Another way to water trees slowly is to make a hole in the bottom (near the edge) of a five gallon bucket. Fill the bucket with water, and leave the slowly leaking bucket under the canopy of the tree. Do this twice or three times per tree, moving the bucket each time.
Sometimes a tree's roots dry out even though it appears the soil around the roots is moist. One way to address this is to use a water probe. These devices work like a long needle and basically pump water into the ground, and are available at your local hardware store or through your landscaper or arborist.
Applying mulch is an excellent way to care for your trees in warm weather; it helps the soil beneath your trees stay cool and retain moisture. Mulch can be made of bark, wood chips, leaves or evergreen needles. Apply mulch within the drip line, at a depth of four inches, leaving a six-inch space between the mulch and tree trunk. Mulch also helps discourage weeds.
Lastly, don't plant annual flowers or other ground covers under the canopy of your tree, as they'll compete with the tree's roots for moisture and nutrients.
Good tree care = a good investment
By providing wildlife habitat, clean air, increased property values, and supplying us with cooling shade, trees enhance quality of life in many ways.
Proper care of our trees — including deep watering of trees during hot summer and warm fall months — will pay you back with big dividends.
For more information about trees and tree care:
Cynthia Orlando is an arborist and recent retiree from the Oregon Department of Forestry
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