Infrequent and deep watering is most effective

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Last Updated: 
July 13, 2006

CORVALLIS - Water your plants deeply to grow deep-rooted, more drought-resistant plants.

Infrequent, deep watering is more effective than frequent shallow watering, particularly for many perennials and larger garden vegetables such as corn and tomatoes, according to the Oregon State University Extension Service Master Gardener Program.

The proper amount of water for a vegetable garden depends on the vegetable type. Vigorous tomato plant roots are known to surpass eight feet. Corn, tomatoes, asparagus, rhubarb, with their deep root systems, should be watered deeply and less frequently than shallow rooted plants such as lettuce, beets, green beans and chard.

Let soil dry out partially between waterings to allow oxygen into the soil. Watch your plants for signs of drought stress, such as dull rather than shiny leaves, then water accordingly.

A good rule of thumb for larger vegetable plants is to apply at least one inch of water every five to seven days during the hottest part of the growing season. Determine the amount and rate of water delivery by placing small empty tuna cans in the sprinkler pattern. For shallower rooted vegetables, water less, but more frequently.

Also, consider your soil type – clay, loam or sand – when planning your summer watering strategies. Clays are slow to absorb or give up water. This is a mixed blessing. Gardens may take longer to water, but they will need watering less frequently than those in sandy soil.

Sand, on the other hand, sucks up water quickly, but dries out quickly. Plants growing in sand will need water more often than soil with more clay. Loamy soils lie somewhere in between clay and sand.

Water flower beds to a depth of about two feet. For fine, clay soil, sprinkle for a total of a half hour, at a rate of two to three gallons per minute per 20 square feet of bed. For loam, sprinkle 20 minutes. For sand, 10 minutes is adequate.

Most trees in Oregon have the majority of their roots in the upper 18 inches of soil. Healthy fruit tree roots generally are three to four feet deep or less, in good soil. Camellias and rhododendron roots reach two to three feet in organic soils.

To deeply water newly planted trees and shrubs, make a small berm of soil to form a catch basin around the trunk. Fill the basin with water, then let it soak in. For sandy soil, do this once. For loamy soil, fill and let water infiltrate twice. With clay, repeat this process three times to adequately water deeply.

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Author: Carol Savonen