Proper landscape irrigation is critical in summer

John Young, Gill, Daniel J., Owings, Allen D.  |  5/15/2009 9:23:54 PM

Sustainable Landscape News Distributed 05/15/09

By LSU AgCenter Horticulturists Dan Gill, Allen Owings and John Young

As we approach the hot summer months, proper irrigation becomes especially important in landscapes. Irrigate when necessary and do so efficiently. Surprisingly, many plants are over-watered rather than under-watered.

Of the tremendous amounts of water applied to lawns and landscape, much is never absorbed by the plants they are intended for. Some water is lost to runoff by being applied too rapidly, and some evaporates from exposed, unmulched soil. But the greatest waste of water is applying too much too often.

By simply using effective and efficient watering methods, you can cut irrigation requirements by 10 to 30 percent and increase landscape beauty and quality dramatically.

Lack of water can cause a plant to wilt, dry up and die. Excessive water can cause root rot; the plant wilts because it is oxygen-starved and, consequently, is unable to absorb moisture. As a rule, plants can withstand moderate drought more easily than too much moisture. For this reason, it’s important to water thoroughly, yet allow the soil to become fairly dry between waterings.

Wilting occurs when roots are unable to supply sufficient moisture to the stems and leaves. Wilting for short periods will not harm plants, but prolonged wilting will cause permanent damage.

Sometimes a plant will wilt on a hot day because moisture evaporates from the leaves faster than the roots can supply water. If the soil is adequately moist, the plant will absorb water in the evening to firm up the stems and leaves. If the leaves remain wilted the next morning, however, watering is recommended.

It’s difficult to make broad recommendations about when to irrigate because of the tremendous variations in weather, but when there is an extended period without rain during summer, newly planted trees and shrubs should be deeply watered once a week. By allowing the soil surface to dry out somewhat between waterings, major root development is encouraged at greater depths where soil moisture is higher.

Plants watered frequently but lightly are more apt to develop roots close to the surface, making them more vulnerable to wilting. This condition happens with automatic overhead sprinkler systems that run for only a short period each night and moisten just the top layer of soil.

Remember that environmental conditions are the primary factor affecting plant watering needs. During cool seasons, less watering is necessary because evaporation from the leaves and soil is slow. Water use under clear blue skies can be twice as high as use under cloudy conditions. The best time to water is in the morning or evening when air temperatures are lower than they are at midday.

In the evening, wet foliage can encourage fungus or mildew, making plants unsightly and jeopardizing their health. Be prepared to control diseases if you irrigate at night.

All trees and shrubs need more frequent watering from planting time until becoming well-rooted, which may take two growing seasons. Once established, water-efficient plants can then be weaned to tolerate less-frequent watering. Proper weaning develops deep roots and makes the plants more drought-enduring.

Water established trees, shrubs and ground covers infrequently, yet thoroughly. In the absence of rain, most trees and shrubs benefit from a once-a-month thorough watering during the growing season. Remember, regular lawn watering is not necessarily a substitute for thorough tree and shrub watering.

The feeding-root system of a tree or shrub is located within the top 12 to 18 inches of the soil and at the dripline of the plant. The dripline is the area directly below the outermost reaches of the branches. Apply water and fertilizer just inside and a little beyond the dripline, not at the trunk. An effective way to water trees and large shrubs is simply to place a slowly running hose on the ground at the dripline. Move the hose around the dripline as each area becomes saturated to a depth of 8 to 10 inches. For large trees, this watering technique may take several hours.

Come to LaHouse in Baton Rouge to see sustainable landscape practices in action. The home and landscape resource center is located near the intersection of Burbank Drive and Nicholson Drive (La. Highway 30) in Baton Rouge across the street from the new LSU baseball stadium. Go online to Louisiana Yards and Neighborhoods for additional information.

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Editor: Mark Claesgens

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