Pernell Gerver's Weekly Columns

Q. I have a sprinkler system in my yard. It waters my lawn and flower beds. My question is how long should the sprinkler system be on and for how often? I don't want to waste water and I'd like to save some money on my water bill, but I don't want my lawn to burn up, either. Thank you!

A. As a general rule of thumb, most plants (including lawn) need one inch of water per week - no more, no less - either from natural rainfall and/or your watering. So if it rains that week and you get a half inch of water from the rain, you would only need to put down a half inch of water. The best way to keep track of how much rain you get is to set out a rain gauge.

For automatic sprinkler systems, as well as manual sprinklers that you set out yourself, I have a tip for determining how long you need to water to get one inch of water. The next time you water, get some small empty cans like tuna fish cans and set them at different locations under the sprinkler. Look at your watch and take note of the time. Turn on the sprinklers and keep an eye on the cans. When one inch of water collects in the cans stop the sprinklers and figure out how long it took. That's the amount of time you'd need to put the sprinklers on if there was no rainfall that week.

Another important consideration when watering is how often to water. It's best to do just one thorough watering per week instead of several light waterings. One thorough watering weekly encourages the plant's roots to go deep into the soil where they're less likely to dry out if a hot, dry spell hits. Short, shallow waterings cause the roots of the plant to grow near the surface where they will dry out quickly.

The best time of day to water is early morning. Water is a valuable commodity and by watering early less water is lost to evaporation. With the misting-type sprayers that shoot up in the air, I've heard that 40 percent of the water is lost to evaporation. Early-morning watering also means less diseases on plants since the leaves have a chance to dry off quickly. Many plant diseases are spread by water.

To conserve and avoid wasting water, it would be a good idea to add to the sprinkler system any type of sensors that shut down the sprinkler system when it's raining. If there's a rain gauge or moisture sensor that shuts the system down when you don't need to water, that would be a good idea to add as well.