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How Much Water is Enough?
by John Harmon
July 6, 2003

I have been getting requests for more information on watering lawns and gardens along with some complaints. The complaint came from a golfer who claims he can't keep his grass the recommended two and one half inches high. That would evidently hamper his efforts to get the ball across his lawn and into the gopher hole. My suggestion of switching to a much larger ball to handle the higher grass was met with scorn. That's evidently cheating.

There is however an easy way to tell when your lawn or garden needs water. The most obvious method is to notice when your plants are starting to wilt and then apply water. You can check moisture levels by working your fingers in to the soil in your garden and when your fingers come up dry it's probably time to water. Another method used in some areas is to measure the evapotranspiration rate or ET. I'm not kidding, the weather stations measure the amount of water given up to the atmosphere by the average lawn and publish this information. You just put that much water back each week. I've never heard an evapotranspiration rate on the local weather forecast but it could happen. The average lawn needs about one inch of water per week except in the hottest weather.

Now the next question burning for an answer is just how much is one inch of water? The simple answer is that one inch equals about 60 gallons per 100 square feet. That's great you say but how do I know how much water my sprinkler put out? In my case it's easy since I haul my water from the river. I know exactly how much water I'm putting on the garden. As far as I'm concerned the lawn is on it's own. I believe that grass, which has been on the planet for many millions of years, got along just fine before I got here and will likely do fine long after I'm gone without any help from me. Besides if I water the lawn it will grow and then I'll have to mow it and that would cut into my naptime.

An easy way to measure how much water your sprinkler is putting out is to place some empty and clean tuna cans out where the water from your sprinkler can hit them. After watering measure the depth in the cans and average them out. It will give you a fairly accurate measurement. I mention using only clean cans because otherwise your local feline may be inclined to make off with your newly acquired rain gauges.

Here's some tips on keeping that water once you figure out how much to put on your garden. Wayne J. McLaurin is an Extension Horticulturist with the University of Georgia College of Agricultural & Environmental Sciences. He says "Once the soil is moist, mulch will help prevent water loss caused by evaporation. Organic mulches reduce the fluctuation of soil moisture and help keep the soil cooler during the summer. In addition, mulches have the added benefit of serving as a barrier to certain soil-borne diseases. Spread organic mulches such as leaves, bark or weed-free hay 3 to 4 inches thick to prevent sunlight from reaching weed and grass seeds. Newspaper, three sheets thick, placed on the soil with organic mulches on top will also conserve moisture and act as a weed barrier. The greater the amount of organic matter in your soil, the better the water-holding capacity it will have. Organic matter in the soil and a mulch on top greatly increase a soil's ability to use water efficiently". Be sure to check with your newspaper publisher to find out what kind of ink they use before you mulch with the local paper. The Yukon News uses a vegetable based ink that is safe to use.

Wayne went on to say that "if possible, apply irrigation in a manner to keep plant foliage dry. Ooze or drip hoses are ideal for this. If overhead applications are made, apply in time for the foliage to dry completely for one or two hours before nightfall. Shallow rooted crops, such as beans and greens, should be watered more frequently with lighter applications than deep-rooted crops".

Another tip from Wayne to keep in mind is to water deeply. Don't stand in the garden and spray the plants lightly every day. This is the worst possible way to water. Water thoroughly to encourage roots to seek water and nutrients deep in the soil. With an extensive, deep root system, plants are better able to withstand dry periods. When watering, soak the soil to a depth of at least six to eight inches. A thorough soaking every four or five days on light, sandy soils and every seven to ten days on heavy clay soils is a good general guide for irrigating vegetables in the absence of rainfall.

More tips include watering early in the day to reduce evaporation loss and allow plant foliage to dry quickly. Wet foliage overnight may encourage some diseases. Drip irrigation or soaker hoses deliver water right at the soil surface and not on the leaves, so you can water most any time. Avoid watering at mid-day. Evaporation losses are highest at this time and don't water when there is high winds because you can lose up to 50 percent of the water to evaporation.

For more information on watering lawns go to

I'm going to stick to my "survival of the fittest" philosophy as far as the lawn goes and I wish it luck!


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