Water trees deeply and regularly when high temperatures hit
When temperatures in Oregon hit the 80's, 90's, and triple digits, it can take a toll on trees as well as people. Large amounts of water evaporate through a tree's leaves. A mature silver maple, for example, can lose up to 50 gallons of water per hour on a hot day.
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 also encourages shallow rooting, which can lead to future health problems for the tree.
One of the first signs that a deciduous tree (i.e., a tree that loses its leaves in the winter) needs more water is leaves that begin to look dull. More advanced symptoms include yellowing of leaves, wilting, and curling at the edges. Leaves may even develop a scorched or burned look - turning brown on outside edges, or between leaf veins. Leaves may also appear smaller than usual, drop prematurely, or turn brown, but remain on the tree. Evergreen needles may turn yellow, red, purple or brown.
For starters, given the benefits and longevity of trees, during prolonged periods of higher temperatures trees should be given a higher watering priority over lawns. When watering, keep in mind that the finer feeder roots that absorb most of the water for your tree are located at or beyond the drip line.
What's a drip line, you ask? That's the circle that could be drawn on the soil around the tree directly under the tips of its outermost branches. Saturate the area within the drip line using a regular hose, or a soaker hose, watering deeply and slowly. Slowly is important, so the water doesn't run off. Soaker hoses are made of porous canvas, plastic, or rubber, and do a good job of allowing water to seep out slowly.
For conifers, water 3' - 5' beyond the drip line on all sides of the tree. Also, if you have a choice, water during the cooler part of the day for all trees.
Another way to water trees slowly is to put a nail 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.
Other tips: mulch can help
Using mulch is a good way to care for trees in hot or dry climates, since mulch helps the soil below trees retain moisture, and stay cool. Mulch can be made of bark, wood chips, leaves and 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.
Do not plant annual flowers or other groundcovers under the canopy of your tree, as they compete with the tree's roots for nutrients and water. If possible, remove any lawn beneath your tree and replace it with a ring of mulch.
Tree care - always a good investment
Trees enhance our quality of life in many ways, providing shade, wildlife habitat, wood and other products, and raising property values. Remember that proper tree care - including deep watering of trees during hot summer months - pays big dividends in the long run.
Cynthia Orlando has a degree in forest management and is a certified arborist with the Oregon Department of Forestry