Watering Practices

Efficient watering practices are important to all homeowners who want to conserve water, maintain a sustainable, healthy turf and reduce maintenance costs. Understanding how grass plants use water and their ability to tolerate dry conditions is the first step to putting the right plant in the right place to perform the right function. This is one of the key concepts in establishing a more sustainable lawn.

Lawn Grass Water Use

Water is an essential ingredient of all living cells. Lawn grasses are about 90 percent water by weight. All nutrients taken into lawn grass roots from the soil are in solution (i.e., dissolved in water). Once roots have absorbed nutrients into the plant, they are moved to the individual cells of the stems, leaves and other grass plant parts where they are involved in numerous plant growth processes.

Water vapor eventually diffuses out of the leaf through small pores called stomata. These small pores are spaced close together on upper and lower leaf surfaces. This evaporation process helps cool the turfgrass plant and its surrounding microenvironment.

Lawn grasses differ in both physical properties that influence water needs and biochemical processes that determine water use. Thus, lawn grasses have a combination of structural and chemical characteristics that make them more or less efficient users of water, as well as more or less drought tolerant. Among our commonly used lawn grasses, the fine-leaved fescues and older, common types of Kentucky bluegrass are more tolerant of dry conditions that either perennial ryegrass or most of the newer, improved types of Kentucky bluegrass.

The depth and extent of root development influences drought tolerance. A grass with a larger, more extensive and deeper root system has an increased volume of soil from which to obtain needed water. This would permit the grass to survive longer under drought conditions. Root development of our common, cool season lawn grasses is generally confined to the top foot of soil.

Determining Amount of Water to Apply

Watering schedules should be managed to replenish the water lost to evaporation and used by the plant. This generally provides a healthier turf and minimizes the potential problems associated with leaching and run-off concerns.

In most years, Minnesota's climate makes lawn watering optional. Water in the landscape is lost back to the atmosphere through evaporation and as used by the plant for cooling purposes (a process known as transpiration). Together these two phenomena are known as "evapotranspiration", abbreviated ET. Potential evapotranspiration is the estimated amount of water a lawn would use if water is always plentiful in the soil. Figure 1 shows the average rainfall and the average potential ET in the Minneapolis/St. Paul area. On average, the amount of rainfall is greater than the amount of water needed by grass plants in each month of the year except June, July, August, and September. Consequently in most years, lawn irrigation during October, November, April and May should be minimal or unnecessary.

The graphs in Figure 1, for an average year, indicate that lawns use about four to six inches of water per month during June, July, and August. The precipitation during each of those months is usually 3 to 4 inches so it is appropriate to schedule lawn irrigation to add about 1 to 1 1/2 inches per week minus any rainfall received during these summer months.

The amount of water to apply depends on the soil type and moisture content of the soil. The preferable method is to thoroughly wet the soil down to a depth of five or six inches. When too much water is applied at one time, much of it may be lost or wasted as it moves too deeply into the soil for the grass roots to be able to use. For example, in sandy, well drained soils it may be more efficient to apply two 1/2 inch applications per week rather than a single larger, one inch application. If the soil is initially very dry, it may take 1/2 inch of water to wet a sandy soil down to a depth of 5 inches, while 1-2 inches of water my be needed to wet a clay soil. Once the soil is thoroughly wet to a depth of 5 inches, any additional water will simply move beyond the root zone of the grass plant.

Puddles Remember that water should not be allowed to run off the surface or to form puddles, as these lead to poor distribution and use of water. Occasionally, the rate at which water can enter the soil is less than the amount applied by the sprinkler after watering has continued for a time. If you notice water running off the surface or forming puddles but you still want to apply more water, turn the water off for 15 minutes then resume watering until the desired amount has been added.

Occasional extraction of soil cores after normal irrigation can give some idea of how deeply you are watering. Another easy method is to sink a shovel into the soil and spread the hole so you can see how far the water has penetrated. Then remove the shovel and press the soil into place with your foot.

Water Sprinkler Determining the amount and uniformity of water applied in a normal irrigation can be done by placing a row of equal-sized, straight-sided cans in a line at one or two foot intervals from the sprinkler and out to the farthest point of watering. After a specified length of time (such as an hour), measure the amount of water collected in each can. This will tell you how much water has been applied during that hour. From this, you can determine the appropriate length of time needed to apply the desired amount of water.

Frequency of watering

Frequency will also be affected by grass species, soil texture, climate, exposure, and amount of use the lawn area receives. Ideally, the grass plants should dictate the watering program. Slight wilting, a color change to a more grayish or bluish-green shade, or footprinting (when plants will not rebound after walking on them) are indications that irrigation is necessary.

It is desirable to keep the interval between watering as long as possible without allowing the plants to go into water stress. Thorough, infrequent watering causes plants to develop deep, strong root systems which can extract water from a much larger volume of soil than the shallow roots associated with light, frequent irrigation (Figure 2).

Some areas of the lawn will probably dry faster than the rest. This is common on southern exposures, sunny areas, borders of sidewalks, and slopes. Hand watering these areas may save water by extending the intervals between watering the entire lawn.

Timing of Water Applications

The most efficient time to water lawns is probably early in the morning hours from 4 to 8 a.m. Less water is lost to evaporation due to lower temperatures and less sunlight. Also, wind velocities are usually lower than they will be later in the day so distribution is improved. Water demand on municipal systems is usually less at that time as well.

Midday watering, though good for the plants since it cools them and reduces heat stress, is not as efficient because some of the water evaporates before getting into the soil.

Watering in the evening should be avoided if possible. If grass plants go into the night time hours wet, they will remain wet for extended periods of time. This may favor the growth and development of turfgrass diseases.

Syringing

Syringing is a very light application of water to wet the leaves of the grass but not necessarily to get water down into the soil. Usually syringing is done during the hot part of the day to reduce heat stress by cooling down lawn and soil surfaces as well as the immediate air surrounding the grass plants.

There are three situations in which syringing might be considered on lawns:

If the turf is infested with one of the patch diseases. Daily syringing during high temperatures can reduce the severity of damage. If the lawn is newly seeded. Germinating seedlings have minimal root systems and can easily die from water stress. Light, frequent watering is necessary until the plants are established and have developed adequate root systems. Syringing during high daytime temperatures will help keep the seedlings cool and moist.
When an established turf is showing stress on a hot day but cannot be watered adequately until later.

Heat, Drought, Summer Dormancy, and Watering Brown Grass Generally, summer dormancy is an important way for our cool-season grasses to survive temporarily hot, dry periods during the summer. During dormancy the plants stop growth of leaves and shoots, causing the existing turf to turn brown. The plants usually do not die, although the leaves cease growing. When adequate water returns, new growth will occur with no long-term damage. The fine-leaved fescue grasses do not go dormant but are quite drought tolerant and grow very slowly under dry conditions, thus using less water.Not all grass plants are sufficiently tolerant of dry periods to go without irrigation in Minnesota. Perennial ryegrass does not go into dormancy but survives temporarily hot, dry conditions by growing more slowly. Some of the newer, improved varieties of Kentucky bluegrass are not as drought tolerant as the older, common Kentucky bluegrass types. Perennial ryegrasses and most of the improved Kentucky Bluegrasses will require some irrigation to keep them alive through hot, dry periods.There are exceptions when it is important to keep the grass growing throughout the summer by supplemental irrigation. Any turf which is affected by or is recovering from past damage such as disease, insects, or excessive weed growth, should receive plenty of water to aid recovery. Any area which has been recently seeded should be watered frequently enough to keep the soil just damp. Newly sodded areas should be kept moist, but definitely not soggy while rooting is established; usually about 3 to 4 weeks. Whenever possible, areas subjected to wear, such as ball fields or play areas, should be watered to maintain tolerance to traffic and aid recovery.Letting the Lawn Go Dormant Dormant When lawn grasses become dormant naturally the soil dries out from the top down. During this process, roots grow deeper into zones of more moisture. When, finally, available moisture within the rootzone has been exhausted, the grasses wilt and foliage browns as dormancy sets in. Stress factors that contribute to this condition include both lack of moisture and high temperatures.Life in the Lawn Grass CrownWhen lawn grasses go into summer dormancy, life does continue in each plant's crown. This is a small mass of tissue about the size of a very small pea located at the soil surface. Roots grow from the lower surface of the crown, and foliage from the upper surface. Healthy, vigorous crowns can withstand dormancy with ease. Weak, diseased, or insect-damaged crowns are less likely to survive dormancy.Start of Lawn Dormancy Brown Grass Dormancy starts with the wilting of lawn grasses. First, a blue-green cast to the foliage develops. At this time, footprints show as people walk across the turf. As the process continues, foliage shrivels, dries and turns brown. High nighttime temperatures (in the 70s and 80s) cause northern, cool season grasses to deplete their carbohydrate energy reserves rapidly. Extended periods of these conditions can cause serious, permanent turf loss.Also, lawns growing on compacted soils are in very vulnerable condition when weather conditions turn hot and dry. Compacted soil prevents the development of a deeper root system and may encourage greater development of thatch (i.e., the brown, fibrous layer of material between the soil surface and the green grass plant parts). A shallow root system accompanied by an excessive (greater than a 1/2 -3/4 inch) thatch layer, provides little protection from potentially serious turf injury and/or loss during extended periods of hot, dry conditions. A watering program will have to be continued to prevent serious turf loss to lawns growing under these conditions. Aerifying the lawn, or better, properly preparing the soil before a lawn is installed, will help encourage a deeper root system and consequently improve the lawn's overall stress tolerance during hot, dry weather.

The process of conditioning your lawn to withstand these hot dry periods is very important to insure its survival and ultimate recovery from summer dormancy. Several important items to help condition a lawn to the warm, dry periods of summer are listed in Table 1. Also, avoid use of broadleaf herbicides during this stress period prior to summer dormancy as injury to lawn grasses can occur.

Table 1. Practices to Increase Turfgrass Drought Tolerance

Choose tolerant species Avoid excessive growth stimulation Maintain adequate potassium levels Raise mowing height Allow turf to harden off into drought conditions
Limit traffic

Generally, there is little that needs to be done to the lawn while it is dormant. However, there are limits as to how much constant hot, dry conditions our lawns will endure. Avoid play or traffic on dormant lawns. Even with properly conditioned turf, applying about 1/4 to 1/2 inch of water every two to three weeks on a heavier soil keeps the grass plant crowns from dehydrating beyond a point of no recovery. Shorter intervals may be needed on sandy soils or during prolonged periods of high temperatures to achieve the same results. Once cooler temperatures and natural rainfall returns in late summer or early fall, resume regular irrigation practices if needed.Recovery from Lawn DormancyDormant lawn grasses recover rapidly upon receipt of a good soaking rain accompanied by soil cooling. Kentucky bluegrasses, fine fescues, perennial ryegrasses and tall fescues, all are able to withstand a certain amount of summer drought without major damage and recover when growing conditions again become favorable. Perennial ryegrasses have changed from 100 percent brown to 100 percent green in four days. Often only a minor lessening of lawn quality is noted at such times. Because it takes some time to establish a balance between top growth and root growth following dormancy, it's good to let the lawn grow taller before resuming normal mowing practices. Do not encourage rapid foliage development with excessive nitrogen fertilizer applications. As growth conditions improve and turfgrasses increase in vigor, core aeration will help to improve the root zone for more rapid recovery. Green Lawn While lawns developed and established to be sustainable usually require less water inputs, carelessly neglecting water needs of the grass plants may destroy all the effort put into creating a sustainable lawn ecosystem. Maintaining grass plant health is still the major objective of any lawn care program. Supplying supplemental water as needed remains a sound management practice for the lawn and the environment.