The top two or three inches of soil dry out first during periods of drought. Plants with roots deeper than that are better able to survive. Too many home gardeners encourage shallow rooting by irrigating improperly. For stronger plants (from turfgrass to trees) change your watering practices to encourage deeper roots.

Folks who go out every day or every other day with hose nozzle in hand or to turn on their sprinklers for an hour (or less) to water part of their yard before moving the sprinkler to a new location are only wetting down plant foliage and making the soil surface damp. This kind of irrigation definitely doesn't provide the same benefits of deeply watering around the base of plants for long enough to wet the soil root zone three inches or more below the surface.

Irrigating frequently but lightly encourages plant roots to grow up toward the moisture. Shallow roots are much more susceptible to wilting to a point where they can no longer service the plant during successive dry spells. The result can be plant death due to drought stress, so a little water applied many times per week can be worse than no watering at all. In addition, water lying on leaves or on top of the ground doesn't help plants much because it typically evaporates into the air instead of soaking into the soil. (Watering at night means less evaporation but that's not good because wet leaves at night promote growth of foliar plant diseases.)

Most landscape plants require an inch to one and one half inches of rain (or irrigation) water every seven days. Limiting irrigation frequency to once a week and watering for a longer period to a depth that encourages deeper roots gives the best benefit for time and money spent to deliver moisture to vegetation. With this type of watering, plants stay healthier and are better able to live through future hot, dry weather conditions.

Garden beds are better off with some type of trickle irrigation such as a soaker hose. Around the base of trees and shrubs let a small amount of water flow from an open hose end until it penetrates the top three or four inches of soil. If you have no other means of irrigation than sprinklers, measure the amount of water applied using a shallow container like an empty tuna can. Make a water-proof mark on the inside one inch up from the bottom of the can. Set this measuring device within the area watered by your sprinkler. After the water in the can reaches the one inch mark, you know plants within the section of landscape covered by that sprinkler have received the minimum weekly allotment of water. Note how long it took to deliver that much water at the usual rate of flow. Time future sprinkler-irrigation sessions to last at least as long. Irrigate only once or twice for that many minutes in any seven-day period with little or no rainfall. (A rain gauge is a good way to keep track of how much natural rainfall your plants are getting.)

Notes related to prior articles on weeds from David Glover, Extension Director for UT Extension Smith County in Carthage: The newer formulation, Preen Plus, contains both Trifluralin (Treflan) and Isoxaben (Gallery) which prevent Oxalis seed germination. The original Preen contained only Trifluralin and would NOT prevent Oxalis. (Readers who might still have the old-style Preen on hand should be aware that it isn't effective against this weed.) I also may have mislead readers in describing crown vetch seed as "airborne." The tiny seeds have no built-in mechanism for long-distance aerial dispersal as do those of thistle and dandelion. However, in my experience, either birds, animals, or the wind have carried crown vetch seeds to my yard from plants growing in my neighbor's ditch to the west (upwind) of my place.

Plateau Gardening is written by Tennessee Master Gardeners about home landscapes and gardening in our state's Upper Cumberland Region. For answers to specific yard and garden questions or to learn how to become a Master Gardener contact UT Extension Cumberland County, P.O. Box 483, Crossville, TN 38557 (phone 484-6743). E-mail inquiries to E-mail may be answered either individually or in future newspaper articles. Visit the companion Web site to view photos and seasonal tips or to see Cumberland, Putnam and Smith County growing conditions.

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