Efficient Water Use on Outdoor Plantings

Water has become an important issue for most Massachusetts communities. As the population and the amount of water used per person continue to increase, the problem will become more acute, especially with a continuing deficiency in precipitation. Some towns have already imposed restrictions on outdoor water use. Home gardeners should be aware of the seriousness of the situation and try to conserve water whenever possible. Here are some suggestions for making the most efficient use of limited water supplies.

Watering Lawns
Although the amount of rainfall received in Massachusetts is generally ample, it is not uniformly distributed throughout the year. Thus, it occasionally becomes necessary to provide supplemental irrigation, especially during the summer months. Water is lost from the plant root zone by gravity, evaporation, and plant use. If plant or soil water content becomes limiting, drought stress and/or turfgrass death may occur.

When is Irrigation Necessary?
Many variables influence the amount of water used by turfgrasses. These include: amount of solar radiation, temperature, humidity, grass species, and rate of growth. Rooting depth and soil texture also affect turfgrass water needs. More deeply rooted grasses can extract water from a greater volume of soil and are thus more drought tolerant than shallow rooted species.

Finer textured soils hold more water than coarse soils and require less frequent irrigation. Because so many factors interact to determine turfgrass water use, it is difficult to give a general estimate of how often to water a lawn. The best technique for determining when to irrigate is to observe both the soil and plant conditions in the lawn and then water it when needed rather than on a particular calendar date.

Turfgrass Drought Tolerance
The following turgrass types are listed in order of their tolerance to drought:

Detecting Wilt and Drought Stress
In order to conserve water and avoid over watering, lawns should be watered just before the development of wilting and drought stress. This may be difficult to determine initially, but a little knowledge and experience will make it easier. Wilting occurs because the plants' internal water content drops so low that the plant cannot remain turgid (stiff), and plant cells begin to shrivel. Turfgrasses undergo a series of visible changes when they begin to wilt. Development of a bluish green coloration and the rolling or folding of leaf blades are two noticeable changes associated with wilting. If footprints remain visible on the lawn for several minutes after walking on it, the turf is not very turgid and wilting is imminent. These initial symptoms of wilting will not cause permanent injury to the lawn. However, they do indicate that the lawn should be watered soon in order to avoid drought stress and possible turfgrass death. In addition to observing plant symptoms, examining the soil is also helpful in determining when to irrigate. Use a soil probe or a garden spade to examine the soil to a depth of approximately six inches. If the soil appears dry, it is time to water.

Effective Watering Practices
Frequent lawn watering often encourages shallow rooting and may predispose the lawn to increased disease and greater susceptibility to stress injury. Watering deeply and less frequently provides for improved turf growth and increased water conservation compared to light, frequent watering. When irrigation becomes necessary, sufficient water should be applied so that the soil is wetted to a depth of four to six inches. This amount of water will vary with soil texture, but approximately one inch of water should thoroughly wet most soils to a depth of four to six inches. Placing several empty cans (tuna or cat food cans work well) under the sprinkler will allow you to determine when an appropriate amount of water has been applied..

You can irrigate your lawn anytime during the day or night. Both day and night watering have their advantages and disadvantages. Midday watering can serve to cool the turf and reduce heat stress on hot summer days. However, if drainage is inadequate, pools of standing water can become very hot and result in turf death due to scalding. Also, midday watering is relatively inefficient due to substantial evaporation losses.

A widely held belief is that night watering will incite or aggravate disease problems. One must consider, however, that the turf is usually wet during the night anyway even if irrigation is withheld because of dew formation. Recent research has suggested that the duration of leaf wetness has a greater impact on disease incidence than night watering per se. In that case, watering during early evening or late morning (just prior to or following dew formation) might result in increased disease by prolonging leaf wetness. Night irrigation helps to conserve water because of minimal evaporation at night. Unless disease is present and actively damaging the lawn, there is little reason to avoid night watering. Late afternoon watering may help to minimize evaporation without aggravating disease activity.

Summer Dormancy Due to Drought
Under periods of prolonged drought, some turfgrasses have the capacity to avoid death by entering into a state of dormancy. Kentucky bluegrass is the most common turfgrass exhibiting this drought avoidance mechanism. Dormant turf appears straw colored and does not grow. When drought conditions cease, usually due to fall rains, the turf is capable of resuming normal growth. Although the lawn may recover when water is no longer limiting, during dormancy it is much more susceptible to disease and insect injury because it is not growing. Also, disease and insect injury often go undetected because the turf is already brown; and thus when damaged plants turn brown they are not noticed. This can result in the loss of large areas of turf which may have been prevented if the lawn had not been dormant. If a quality lawn is your goal, drought induced dormancy should be prevented by timely watering.

General Tips for Watering Outdoor Plants
During dry seasons, watering is necessary to maintain healthy plants. Water is more important for new plantings than for established ones.

In trying to conserve water and to realize greatest benefit from water used, it is wise to set up a regularly scheduled program.
· Do not try to water all planted areas at each watering.
· Section off your areas, and concentrate on these areas individually for maximum benefit.
· Saturate each area, and then allow to dry out before watering again.
· Plan to use mulch around all planted areas to reduce water loss.
· Do not allow plants to wilt before beginning a watering program.
· Remember, two hoses at low pressure without a nozzle is the best method of watering.
· Overwatering can be more harmful to plants than underwatering. Roots need air as well as water. Do not keep soil saturated with water continuously.

Watering Trees and Shrubs - Established Plantings
Established trees and shrubs do not require as much water as new plantings, but during July and August some watering may be necessary. Basic principles include:
· Watering with a hose and nozzle is not recommended. Merely syringing the plants and soil is of little value to the root system through which water is absorbed.
· An open hose placed at the base of a tree with the water flowing slowly will provide needed water to the root zone. If the water is allowed to trickle into the soil gradually, it will seep down and saturate the area around the roots. Since the composition of soils varies, the rate of absorption will vary, but the water pressure should be as high as possible without surface run-off.
· By saturating the soil around the plants, less frequent watering will be necessary. Each plant or bed should be saturated approximately once every two weeks or less depending on the weather.

New Plantings
New plantings will require more frequent watering than established plants. The same type of saturating should be exercised, but once a week may be necessary for new plants. A ring of soil around newly planted trees and shrubs in the form of a saucer is recommended. This could be built from gravel or excess soil after planting. Fill the ring at each watering to allow gradual seepage into the soil. For the first month, water new plantings twice a week, then weekly for the rest of the season.

Mulching can help to reduce water loss. The use of mulch on new or established plantings is an excellent method of conserving water. Beds which are exposed to the sun and drying winds without cover will dry out rapidly. Trying to keep these areas moist by watering is not adequate, and a great deal of water is wasted.

Some of the more common materials used for mulching are peat moss, wood chips, straw, salt marsh hay, sawdust, pine needles, hay, leaf mold, compost, dried bark, leaves and many others. Much less water will be required to maintain vigorous plants with the use of a two-inch mulch.

Watering Flower and Vegetable Gardens
Annual and perennial gardens should be watered in the same way as trees and shrubs. A fine-textured mulch or soil conditioner such as peat moss should be used to help hold the moisture. Flower and vegetable gardens may require more frequent watering. Again, merely sprinkling the beds lightly each day will not be adequate for efficient water use. Saturate the areas once or twice a week during drought periods, and watch the plants closely. If wilting occurs, water should be applied more often; but under normal circumstances twice a week should be ample if a mulch is used.

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