Water is essential to both plant and animal survival. Landscape plants require an inch to one and one half inches of rain (or irrigation) water per week. When you irrigate, how moisture is applied and at what frequency is important. Limiting irrigation to once or twice per week and watering for a longer period each time, encourages deeper roots and gives the best benefit for time and money spent When plants experience stress from lack of water they develop all sorts of problems just as people suffer various life-threatening effects from dehydration. Some tree and shrub maladies can be avoided by proper irrigation.

Sometimes you can keep trees from uprooting and prevent property damage by irrigating Tree roots do more than just bring water in, they also anchor the plant in place. Ground that gets no water for a long time does not stay firm. Excessively dry roots become permanently injured. You may have seen large trees in Tennessee yards that toppled after soaking rains because the roots lost their hold on parched earth prior to the storm. This is especially hazardous if that tree is close to a residence or parked vehicles.

Certain beetles and moths bore into woody plants. Some like the emerald ash borer carry pathogens for plant diseases. Boring insects are a greater threat to trees and shrubs suffering from lack of water. Turgor is a natural plant defense against borers. It is similar to blood pressure in the human body. The flow of water within a plant, creates inside pressure known as “turgor pressure.” Water moves constantly up from roots to foliage then out to the rest of the plant. When soil moisture is readily available, turgor pressure from this constant flow of liquids stays high. Boring insects and their larvae find it difficult to force their way into the plant’s interior when turgor pressure pushes from within. However during drought, turgor pressure drops. Harmful beetles and moths find getting inside easier. Once under cover of the bark, it is almost impossible to reach those insects with insecticides. Irrigation during dry spells helps control boring insects naturally by elevating turgor and is one of the few effective preventatives.

It can be satisfying to stand, hose nozzle in hand as you water, but that irrigation method isn’t efficient. Plant roots need a deep soil drenching Another bad practice is setting automatic sprinkler systems to come on for a brief period every day. Frequent, light watering dampens only the ground’s surface and encourages shallow rooting. Change your watering practices to encourage deeper roots. The pay-off will be stronger plants from turfgrass to trees.

Use trickle irrigation for garden beds. 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 to six inches of soil. If you must irrigate using sprinklers, be sure to measure the amount of moisture applied with a shallow container like an empty tuna can. Make a water-proof mark on the inside one inch up from the bottom Set this measuring device within the area watered by the sprinkler. After water reaches the can’s one inch mark, plants in that area have received the minimum weekly amount of water. Make a note as to how long it took to deliver that much moisture. Time future sprinkler-irrigation sessions to last at least that long. Irrigate only once or twice for that many minutes whenever no rain or less than an inch of natural rain falls during a seven-day period, as measured by a rain gauge. Irrigating this way should help plants stay healthier and better able to live through future hot, dry weather.

Plateau Gardening is written by Tennessee Master Gardeners about home landscapes and gardening in our state’s Upper Cumberland Region. Contact UT Extension Cumberland County, P.O. Box 483, Crossville, TN 38557 (phone 484-6743) for quick answers to specific questions, free publications, or to learn about becoming a Master Gardener. Send comments or yard and garden inquiries to Master Gardener Rae at mgardenerrae@frontiernet.net.

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