Lawn Care: How To Water Your Grass

Plants need water for germination, growth, photosynthesis, and temperature control. They need enough of it to dissolve and absorb nutrients from the soil to assemble the food manufactured in their leaves. About 90 percent of the water that plants absorb transpires into the air for temperature control. When they transpire more water than they absorb they take up fewer nutrients, and stop photosynthesizing. Then they wilt and eventually turn brown. Grasses have evolved to survive dry spells, however, by going into dormancy. The shoots and foliage die, but if the crown and rhizome, or stolen buds survive, their tissues will start new growth when moisture returns.

Grasses differ in drought tolerance. As a rule, however, tall grasses with deep, well fed roots survive droughts best. Deep, infrequent watering encourages root development, and 12" of water penetration is about right.

How much water should you use when watering your lawn? Deep watering takes the mechanics of soil moisture into consideration. Soil dries out from the top down. Good soils soak up water, hold it awhile, then let it drain down slowly. Clay takes a long time to absorb water, holding it so tightly that it does not drain away quickly and can even suffocate the plant. Sandy soils absorb water quickly, but it drains right out again. The best soil is a loam with enough clay and silt to hold moisture but enough sand to encourage good drainage,

If a lawn wilts fast as the ground dries out in spring, chances are that it has short roots, and the water has dropped below them after the top inch or two of soil dries out. A lawn like this will need water often and always have a damp surface, which favors weeds and fungus. If a lawn has deep roots, the top inch or so can dry out, discouraging weeds and fungus while the lawn draws water from deeper in the ground.

To get a deep-rooted lawn, keep watering it in spring until it grows about 2" or 3" high. Then start mowing, but not too short. The leaves will be manufacturing plenty of food; so stop watering. Keep up the mowing schedule, but let the soil dry out so the roots will have to reach deeper for water. Don't water again until the turf starts to wilt. A wilting turf turns bluish green or shows footprints. When you water do it for a long time, at least an hour or two, perhaps more, to let the water to soak deep. Don't water again until the lawn wilts again.

Watering has to be evenly distributed over the lawn for uniform growth and appearance. If the lawn has dry patches, measure water coverage in containers spaced evenly under the sprinklers. You may need to supplement automatic sprinkling with hand watering to wet the dry patches. To control water waste because of run-off, encourage the use of low-flow sprinkler heads. Since water flows downhill, sloped lawns won't need as much watering at the bottom as the top.

You can test for penetration with an expensive electronic moisture tension sensor or by slicing into the lawn with a spade and feeling for dampness at the bottom of the cut. There are also soil coring tubes that let you extract a core of turf and soil to test for moisture penetration. It's a good way to inspect soil texture and structure, as well.

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