Irrigation water will be turned off today or next week depending on your district. That means you still have a day or so to provide trees, shrubs, perennials and lawns with a deep watering. I know I have talked about fall watering, but it is an important garden chore that can not be emphasized enough.
Luckily, this year we had plentiful irrigation water, and our plants were not forced to endure drought conditions. However, once the irrigation water is off, there will be little natural precipitation to replace water lost during dry, mild fall and winter weather.
Keep in mind that only a little over half of our 6 to 10 inches of annual precipitation occurs during the fall and winter months. This is not enough to replace the water lost from the soil through evaporation and through the needles and leaves of evergreens, such as pines and rhododendrons. As a result, the roots of plants may shrivel and die from dessication. When the plants resume growth next year, the injured root systems may be inadequate to support top growth, weakening the plants and making them more vulnerable to attack by insects and diseases. When severe, it can also lead to dieback or even plant death.
To help your trees, shrubs and perennials survive winter, use these next few days to apply enough water to moisten the soil to a depth of 12 to 18 inches. When watering trees, apply water at the drip line, and water shrubs similarly.
The drip line is the area below and just beyond the reach of the outermost branches of the tree's canopy. Water applied at the trunk or inside the drip line is not used and can lead to rot at a tree's base. When multiple shrubs and flowering perennials are in beds, water the entire bed to make the task easier.
Once irrigation water is turned off and lines are blown out to protect them from damage, your watering chores are not over. You will still need to deep water your plants once or twice a month until March or April. However, do not water during very cold weather (when daytime temperatures are below 40 degrees) or when the soil is frozen.
I can hear you grumbling, but this is important in protecting the health of trees and shrubs. Keep a hose handy for watering through the fall and winter months. Soaker hoses work well for deep watering.
-- Marianne C. Ophardt is a horticulturist for Washington State University Benton County Extension