Last Word on Lawn Irrigation

As our weather keeps changing I continue to alter my sprinkler timer's programming to accommodate. Lately, I've decided that it is too complicated to explain watering by irrigation scheduling alone. It's a lot simpler to explain what the goal actually is.

To keep a lawn thriving we must maintain moist soil down to a depth of at least 8 inches. To determine soil moisture I keep a 4-foot long, 3/16" diameter steel rod (3/16" to 3/8" diameter is OK ) near my lawn. (A wooden dowel or a fiberglass rod are also suitable) I can push this rod, with minimal effort, as deep as the soil moisture extends into the ground. When the rod hits dry soil it stops. In my lawn it typically ranges from 6", on the drier sloped areas, to 20", in the low areas next to my drains. The goal is to maintain the soil moisture to a depth of about 12".

It really doesn't matter if you water your lawn 3 times per day, 1 time per day, every 2 days, or every 3 days. It is the soil moisture depth that is important. It is easier to maintain proper soil moisture when irrigated daily, but the lawn gets fewer weeds (especially oxalis) when watered less frequently.

I normally irrigate my lawn between mid-morning and noon. My sprinkler timer waters for 4-5 minutes at a time. (Longer periods are inefficient due to run off.) If required, my sprinklers cycle on several times per day with a minimum of 1 hour between cycles. During hot weather I water 2 or 3 times every day. During cooler conditions I water 2 times per day, but only every 2-3 days. There a probably dozens of schedules you could set your timer to that would accomplish your goal.

What I have found is that it takes many days to change the moisture level in the soil. If your soil gets too dry, it takes 3-5 days of additional watering to remoisten the soil to the proper depth. Watering a dry area by hose takes many hours to be effective. Once the moisture level is corrected, dry areas in a lawn will regreen within 10 days.

Written By Gary Matsuoka