While most people think of a lack of water, beware of over-watering. It is easy to over-water a turf area. The consequences of over-watering are not always obvious but can cause a decline in turf quality. Some potential consequences of over-watering are :- increased amounts of Crabgrass, increased disease incidence, shallow rooting, waste of valuable resource, and higher water bills. When watering a lawn it is best to err on the dry side rather than be guilty of over-watering.

Frequency of Watering.

The frequency of watering will vary from site to site and should be determined by the appearance of the turf. This can be determined because the first signs of water stress in a turfgrass stand are bluish-green colour, and footprints remain in the turf after walking on it. The footprints remain because the leaves are unable to regain their configuration due to a lack of water. (Turgidity). Ideally, the turf should be watered at this point. Turfgrasses can easily withstand this much water stress without a decline in turf quality, and there is no real benefit to watering a turfgrass stand before this point.

As the degree of water stress increases the turf will wilt and have a greyish green colour. Turf that has wilted should be watered without delay. Wilted turf will recover rapidly following watering. Severe drought stress will cause the plants to cease growing and the leaves will turn brown and possibly die. Watering at this point will help the turfgrass plant survive, but will take about 2 weeks until the turf produces new leaves and recovers completely.

Turf, should not be watered by a set schedule. A set schedule does not take into account the needs of the turfgrass plants. Scheduled watering may lead to over-watering. In addition to wasting water, over-watering increases the amount of weeds present in the lawn and creates a favorable environment for diseases.

Homeowners with automatic irrigation systems should not set timers and clocks and use the same irrigation program for the entire summer. The program should be changed according to the needs of the turfgrass plant. The automatic irrigation system should be set to start for a single irrigation cycle only and then shut off until the turf requires water again.

Amount of Water to Apply.

Most lawns in temperate zones will need from 25 mm to 35 mm of water per week. It is best to apply this amount of water in a single thorough soaking, or two equal applications of water three to five days apart rather than in light irrigations every day. The soil should be wetted to a depth of 150 mm following and irrigation. A complete wetting of the turfgrass rootzone  is the most beneficial for turfgrass plants. Daily light irrigations promote shallow rooting, nondrought hardy turf, and encourage weeds.

Sprinklers attached to a 15 mm hose usually apply small volumes of water to a turfgrass area. Therefore, most sprinklers should be left in one location for 2 to 3 hours to thoroughly wet the turfgrass rootzone. Automatic irrigation systems with spray heads that distribute water in all directions simultaneously are capable of applying a large volume of water in 10 to 15 minutes.

Automatic irrigation systems with rotary sprinkler heads that have one stream of water are capable of applying the necessary water in 30 to 40 minutes.

To determine the amount of water being applied by any one sprinkler, place shallow, straight-sided containers, such as empty tin cans, in a grid pattern around the sprinkler. Turn the sprinkler on for a specified length of time and then measure the water collected in the cans with a ruler. This can be used as a guide in determining the amount of water applied.

Time of Day to Water

The ideal time of day to irrigate is from 4:00am to 8:00am. At this time water pressure is usually the highest, there is little distortion of the watering pattern by wind; and the amount of water lost to evaporation is negligible. Although the early morning hours are ideal for watering, this is not a convenient time for most people. The second best time to water is from 8:00pm to 12:00pm. Usually distortion from the wind is not a problem at this time and loss from evaporation is slight. A major problem may be lack of water pressure for those using municipal or city systems. A potential problem caused by watering in the early evening hours may be greater incidence of disease. The problem can be reduced by watering only when the turf needs water and by watering infrequently but deeply.

Watering an established turf during midday is not very effective. A large amount of water is lost through evaporation, making it difficult to thoroughly wet the soil. Although not recommended, midday watering does not cause the turf to burn, except in very dry , hot areas.

Rate of Application

Slopes or areas of soil compaction are often difficult to water without the water running off. On these areas it is important not to apply water faster than it can be absorbed. One possible method to irrigate a slope is to water for a period of time until the water begins to run off and then stop. Allow water to penetrate and infiltrate into the soil and then water the area again until runoff just begins.Repeat this cycle several times until the soil is wet to a depth of approximately 150 mm.

Dormancy.

In situations where a lawn is not watered and rain is limited, the lawn will wilt and the leaves turn brown. These lawns are not necessarily dead; the turf could be in a dormant condition depending on the type of turfgrass species.

Dormancy is a natural survival mechanism of the turf plants. The leaves are dead but the crown (growing point) and the root system remain alive. A turfgrass plant loses water through the leaves. When the leaves are dead, little water is lost. This conserves water and allows the crown and the root system to remain alive. Turf can survive 4 to 6 weeks in a dormant condition without significant thinning of the turf upon the return of favorable moisture conditions.

After 4 to 6 weeks of dry conditions the dormant turf should be irrigated with 10 to 15 mm of water in one thorough irrigation. This amount of water will not cause the turf to green up but will provide moisture to help the crown and root system survive. If the dry weather persists, water dormant turf with 10 to 15 mm of water every two weeks can survive until optimum conditions occur again. Following the onset of favorable moisture conditions, either through rainfall or irrigation, the turf will develop new leaves and begin to grow actively.

Special Situations

A newly seeded lawn will need to be watered two to four times per day. The seed bed should be moist to a depth of 25 to 50 mm, but not saturated. As the seed germinates the seedlings begin to grow, it is essential that the new seedlings are not allowed to dry out. Continue to water the seedlings two to four times per day if the weather conditions are dry. When seedlings reach 50 mm in height, gradually start to reduce the frequency of watering and water more deeply. After the new turf has been mowed two or three times, deep, infrequent waterings are the best.

A newly sodded lawn will require water one or two times a day. Sod should be watered so that the turf sod strip is wet the entire thickness and the soil underneath is moist to a depth of approximately 25 mm. Over watering sod is a common mistake. Do not saturate the soil below the sod. This will inhibit roots from sod growing into the soil. As sod becomes established and roots penetrate and grow into the soil, gradually reduce the frequency of watering but wet the soil to a greater depth. After the sod has been mowed three or four times, deep, infrequent watering should be practiced.

Clark Thorssell and Zachary Reicher  Purdue University, West Lafayette, IN U.S.A.