Questions on: Watering
Ron Smith, Horticulturist, NDSU Extension Service
Q: We have four or five houses in our development that have automatic sprinklers. The rest of us water with hoses. When it gets hot in the summer, we run short of water in our supply tank. We have to water on even or odd number days according to our house numbers. How much water is needed for a lawn to maintain a green color? How much water should a lawn receive per week? What is the minimum? How long should an automatic sprinkler run to get the right amount of water on the lawn? We have some people that want a green lawn no matter what and they will use however much water they want to keep a green lawn. (Mandan, N.D.)
A: Forget the odd or even watering. Instead, water as needed. I know that probably will not get approved, but on an odd or even basis, people figure they have the right to water even if itís not needed. As a sweeping generalization, lawn sprinkler systems will deliver one inch per hour using a fixed spray. With the rotaries that are used on larger areas, anywhere from 1/4 to 2/5 inch per hour is delivered. To figure out what one inch of water is, calculate it on an acre-inch basis, which is 27,152 gallons. If a 10,000 square foot lawn is being watered, that is approximately 23 percent of an acre, so 23 percent of 27,152 is 6,245 gallons of water needed to apply one inch to 10,000 square feet. A Kentucky bluegrass lawn, if it is not over-fertilized, and is mowed at the optimal height, which is 3 inches with the clippings left on the grass, can get by and still look green on 80-85 percent of the PET (Potential Evapo-Transpiration - assuming an average of 0.20-0.25 of an inch per day) rate. The water required is then about 5,000 gallons. People with an automatic system should make sure no water is being wasted on drives, walks, sides of buildings or streets. They should water in the early morning hours, setting their controllers to start watering at 3:30 or 4 a.m. With the fixed sprays, a run time of 20 minutes will deliver about 1/3 inch of water. Not all exposures will need that much water each time (such as the east and north exposures). They should not water to the point that runoff is taking place because that is wasting water. Assuming there is no runoff and watering takes place in the early morning hours, under the worst conditions, the lawn would need watering three times a week to deliver a total of one inch of water to keep the grass green. Now that all of this has been said, one can greatly reduce the amount of water and lower the water bill by allowing the grass to go dormant (turn brown). Once in that state, a light watering every other week of 1/4 to 1/3 inch will keep the crown of the grass alive and allow it to turn green once the cooler autumn weather returns and hopefully, more frequent rainfall. Wind is another issue. It is stupid and very wasteful to run an irrigation system when the wind speed is above 10 miles per hour. The sprinkler pattern is distorted, the application is uneven and water is often carried onto non-living areas. If itís always too windy in your development, have the sprinklers refitted with lower trajectory nozzles which will cut down on the drift.
Q: I'm planning to patch an area of lawn where I trenched in an underground water pipe. The soil is predominately shale and I believe some clay. The trench is approximately 12 inches wide by 140 feet long. It is on the edge of the lot alongside a lilac hedge. What is the best type of lawn seed mixture to use? (Jamestown, N.D.)
A: I would go with a creeping red fescue such as Dawson, ruby, or navigator. Itís a tough turfgrass species, needs little water, helps to sequester weeds, germinates rather quickly and looks good.
Q: Over the winter piles of snow gather in certain spots on the lawn. In the spring these snow piles turn to ice until everything melts. Consequently, these spots remain bare during the summer. The surrounding grass will not spread over onto them. Sowing grass seed onto them does not help either. What is wrong and what can I do about it? (Mina, S.D.)
A: These areas are usually surface "sumps" where, when it rains or snows, the moisture collects and causes havoc with growing grass. If you can, core aerate, and bring in some fresh topsoil to spread lightly over the area. Then spread the seed, working it into the upper 1/4 inch of soil.
In spreading the soil, try to slope or grade it in such a way that water or snow will not collect and turn into ice, but run off or percolate into the soil below.
A: No, unless it goes a whole month without water. Cool season grasses, which most home lawns are, tend to go dormant during extended periods of hot, rainless weather.
A: Most likely it is the heat. Try to maintain a consistent moisture level by watering every other day during heat stress. As to whether or not it will recover, only time will tell. Kentucky blue is fairly tough stuff and has the ability to bounce back from hot spells. A lot depends on the maturity of the crown of the plants and whether or not they dehydrated completely to the point of death and not just dormancy.
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