WHAT IS THE BEST WAY TO WATER GRASS?
, 7 min reading time
The answer to this question depends on several factors. These include the type of grass you are growing, soil type on the area, and the climatic conditions where you are located. It also depends on whether we are talking about newly seeded grass, or well-established turf.
Let’s start with new seedings. Until grass has developed an extensive root system, it will be very sensitive to drought and can die in a single dry and windy afternoon if it is not watered. This is particularly true of small-seeded grasses that are planted close to the surface of the soil. Larger seeded grasses that are planted a little deeper can tolerate more drought, but even these grasses are easily killed by drought in the first few days following germination. When grass first germinates, it will put down a primary root that stabilizes the plant for further development but is not very efficient at obtaining enough water for growth. At this stage, the new seedling can easily dehydrate and die and it is critical that it has enough moisture until a more extensive root system can form. When the grass has matured in a few weeks after germination, the root system extends into the surrounding soil and the plant can tolerate longer periods without irrigation.
Right after seeding, water the surface with approximately one quarter inch of water. This should be the right amount of water to begin the germination process without causing erosion of the surface soil. In the next few days, lightly water to keep the surface moist. How often you need to water will depend on weather conditions. Hot dry winds are particularly a problem in the first few days after germination and it is critical that the area is not allowed to become excessively dry, particularly in the afternoon on hot windy days. The amount of time required for germination varies with species. Perennial ryegrass is fast, two to three days, and Kentucky bluegrass is slow, one to two weeks. The critical time is shortly after first emergence. For the two weeks after emergence the area should not be allowed to dry. After a few weeks, the root system will have matured sufficiently so that you can cut back to a single watering per day.
It is easy to overwater, particularly if you have an automatic irrigation system. Watering two or three times a day during the first couple of weeks will be sufficient, unless it is particularly windy and dry. A couple of tenths of an inch per application will be sufficient unless the soil is very sandy. I have seen people set up the irrigation system every 15 minutes and soon water is running down the street. That is too much. As long as there is moisture just below the surface, that is sufficient. Once emergence has taken place and there is green grass on the surface, you can cut back to once a day or even once every two days.
On areas where irrigation is difficult or impossible, mulch can be used to hold moisture for germination. Mulch is anything that will temporarily cover the soil to prevent drying, without interfering with seed germination. Straw can be an effective mulch. I will deal in more detail with mulches in another article.
Once the grass is established you can reduce irrigation. In some climatic zones it is possible to rely on rainfall and no irrigation will be necessary. This is particularly true if tall fescue which has a very extensive root system.
The best way to irrigate mature turf depends on many different factors. These include the species of grass, the type of soil it is being grown on, and the climatic conditions in the area. There is no single right answer that covers every situation.
Let’s begin with the grasses. Warm-season grasses tolerate drought much better than cool-season grasses. This is due to their C4 photosythetic system (see DO I NEED A COOL-SEASON OR A WARM-SEASON GRASS?) in this series. They also have a deeper and more extensive root system that makes them more efficient at obtaining water from the soil. Therefore, it is going to take less water to maintain them. In regions like mid-section of the United States, where you have a choice of warm-season or cool-season grasses, cool-season grasses are often chosen because of the fact that they remain green well into the fall and green up early. Warm-season grasses on the other hand will remain dormant much of the year. However, the warm-season grasses will take far less water on an annual basis to maintain them.
Another major concern is soil type. The clay-loam soils are the best for water conservation. They provide an ideal media for rooting and they maintain a maximum of plant available water. Sand can be a good media for growing grass and we often replace soil with sand on sites such as golf greens and sports fields because they provide excellent drainage and prevent standing water from interfering with play. However, sandy soils are not very efficient from an irrigation standpoint. The water applied on sands quickly drains away, requiring more frequent watering. Clay soils also present a problem for irrigation because they drain too slowly. Rainfall and excess irrigation may run off from the surface before the water penetrates the soil.
When it comes to watering grass on a good clay-loam soil, the key words are “deeply and infrequently”. Ideally, you want to put on enough water to reach the bottom of the root system and then let the grass go without additional irrigation for a few days. One of the best ways to determine if more watering is needed is to look at your footprints on the lawn. If the blades of grass are turgid and springs back readily, they have enough water. If the blades do not spring back readily and you can see your footprint for a few minutes, the grass needs to be irrigated. This watering procedure is good for the root system and will result in deeper, more extensive roots that are more efficient at removing water and nutrients from the underlying soil. The worst way to water grass on a clay-loam soil is lightly and infrequently. This will result in a shallow, less efficient root system.
Sandy soils are different. Deeply and infrequently will not work on sand. These soils require lighter applications of irrigation water on a more frequent basis. Heavy clays will also require more frequent watering with smaller amounts of water in each application.
On average, grass grown on clay-loam soils will require about one inch of water per week, either from rainfall or irrigation. The grass may need a little more water in hot dry conditions and a little less in cooler conditions, but this is a good goal for proper irrigation of turf. You may be able to put the whole inch at one time on some clay-loam soils. On sands and clay soils you will want to water with one quarter inch or less per application.
To determine how much water your hose system or underground irrigation system is delivering per unit time will require a little experimentation. Put out tin cans or other catch devices surrounding the irrigation head and measure the amount of water delivered in a certain amount of time. If your system measures in gallons, it takes 27,154 gallons to apply one inch of water to one US acre (43,560 sq. ft,). Once you know this useful conversion factor, you can measure your lawn and calculate the depth of water that has been applied.
Nick Christians, University Professor of Horticulture, Emeritus, Iowa State University
books: http://www.amazon.com/Nick-Edward-Christians/e/B001H6SB7A/ref=ntt_dp_epwbk_0
turf blog: http://www.iaturf.blogspot.com/
Fundamentals of Turfgrass Mgt. 5th ed http://www.wiley.com/WileyCDA/WileyTitle/productCd-1119204631.html
Web site: https://www.hort.iastate.edu/directory/nick-christians/