Time for a Lawn Audit?

In this article we will look at lawn water usage. The Sunset Magazine article titled "How much water does your lawn really need?" is an excellent source of information. Now is the time to prepare for saving water during the summer months and a lawn audit is the place to start.

You may be killing your lawn by using too much water
Did you know that more than half of the water used by a typical single family residence goes outdoors—mostly to lawns. Studies consistently show that most homeowners apply at least twice as much water as their lawns actually need.

Over watering yields a shallow-rooted lawn and can leach fertilizers and nutrients out of the root zone. Supplying too much water also causes grass to grow faster, which means more Saturday mowing for you. Over watering can also encourage disease problems that must be treated with expensive and often toxic chemicals.

When good sprinklers go bad
Before performing a lawn audit, it is a good idea to check the operation of your sprinklers. Since sprinklers are usually set to run in the early morning, it is very difficult to see if the sprinklers are operating properly. Lots of problems can be traced to faulty or improperly adjusted sprinklers that the owners simply weren’t aware of. Run the sprinklers manually before performing the lawn audit to spot problems.

The Lawn Audit
(15 minutes)
The Lawn Audit can help you figure out the consistency of your sprinkler system and also to find out how much water your lawn is getting; best of all, it only takes a few minutes. Here’s how to do a lawn audit.

1. Measure sprinkler output by placing five or more straight-sided cans or coffee mugs randomly around your lawn. Run your system for 15 minutes
2. Measure the amount of water in each cup; note the lowest amount.

What the Lawn Audit Means
Performing a watering audit gives you more information than simply how much water your lawn is getting. The fact that each container has accumulated a different amount tells you a lot about the uniformity of your system. If there is more than a 1/4-inch difference between containers, you may want to adjust or change sprinkler heads or experiment with the positioning of hose-end sprinklers.

Once you have achieved a more consistent watering pattern, rerun the test. Again, note the container that accumulated the least water. Now it's time to use the ET chart to determine the number of minutes to water twice a week.

How to Use the ET Chart
What's ET? It means evapotranspiration, the sum of evaporation from soil and plant surfaces (E) and the transpiration that takes place from plant leaf surfaces (T). Basically, this is the amount of water in inches that needs to be replaced by irrigation to keep the moisture levels up for the lawn to stay healthy.

The chart at the below shows the number of minutes to leave your sprinklers on for adequate twice-weekly watering, based on the sprinkler output figure you discovered in your lawn audit.

For example, for March watering look at the Spring column. Choose the water depth closest to your lowest sprinkler output. Then read down until you reach your city, or nearby one with similar climate. That is the number of minutes to water twice weekly.

You may have to adjust the time given to suit your sprinkler output. If your output figure is 3/4 inch, water for a third as long as the minutes given in the 1/4-inch column. If the figure is 1 inch, water for a quarter as long.
Times given are for cool-season grasses - bent, bluegrass, fescues, and rye grass the types usually planted in the Bay Area. For warm-season grasses, such as Bermuda, St. Augustine, and zoysia, water 20 percent less.                                                       

Lawn does not live by ET Chart alone
Use the ET chart as a guide. Since your own lawn has its own mix of grass, soil, slope, shade, orientation, and thatch, you may need to fine-tune the watering times over the season. Observe your lawn for a few weeks after performing the lawn audit.

If your lawn is drying out, it will turn from bright green to dull blue- or gray-green. Walking on it, you can look back and see your footprints, because the grass no longer springs back from your weight. Usually one spot will dry out before the rest. If your lawn is drying out either water for slightly longer periods or for shorter periods but more frequently.

Perhaps, instead, you suspect you’re over watering. Cut back the volume or frequency until the lawn does begin to dry out between waterings, then add a few minutes to get back on track.

You also need to consider the weather.

Clear skies and high temperatures--especially if it's windy--greatly affects ET. On a dry, breezy day in the 90’s, your lawn probably gets as thirsty for a cool drink as you do. Similarly, summer showers, clouds, or unseasonally cool weather may let you postpone watering for a few days. Pay particularly close attention to your lawn's diminished needs as the weather turns cooler in fall--that's when a lot of home gardeners fail to cut back on watering.

Also, when possible, water your lawn when the air is still, such as in the early morning.

Remember the lawn audit and ET Chart are used as guides to help you save water while keeping your lawn looking and feeling its best.