Summers in our region can be brutally hot and, frequently, extremely dry. That’s why knowing how and when to apply the cooling, moisturizing effects of irrigation can be so critical to the health of a lawn in summer.
Most varieties of lawn grass need about 1” of water per week in summer, either through rainfall or irrigation. A dark, bluish-gray color, foot-printing (when footprints on the lawn remain after 30 minutes) and wilted, folded or curled leaves indicate that the grass is under drought stress and that it’s time to water.
One of the keys to a grass variety’s drought resistance is the length of its root system — the deeper the roots, the more access the plant has to below-ground moisture. Unfortunately, many people set their irrigation systems to water for only a little while every day, which encourages the grass roots to stay near the soil surface, making them more vulnerable to heat and drought. Instead, the general rule of thumb is to water deeply and infrequently (only when the lawn is starting to show drought stress), although sandy soils that don’t retain water well may require more frequent watering — for example, 1/2″ of water every third day.
Water the lawn to a moisture depth of 4” to 6”. Probe with a screwdriver to determine how deeply the water is moving. Depending on the irrigation system, it may be necessary to irrigate an area for three to five hours in order to apply 1” of water (it takes 620 gallons of water to apply 1” of water per 1,000 square feet).
If possible, irrigate early in the morning, from 6:00 a.m. to 8:00 a.m. Heat and wind speeds are lower at this time of day, so there is considerably less loss of water due to evaporation. Avoid watering at night — prolonged wetness on leaf blades is conducive to disease development.
Special considerations for newly sodded lawns
The tips above are for well-established lawns where the grass has had plenty of time to root well into the soil. Newly sodded lawns, though, require extra TLC. In particular, new sod has crucial watering needs.
Begin watering new sod within a half hour after it is laid on the soil. Apply at least 1” of water so that the soil beneath the turf is wet. Ideally, the soil 3” to 4” below the surface should be moist.
For the next two weeks, keep the below-sod soil surface moist with daily (or more frequent) watering. Pull back a corner of the turf, and push a screwdriver or other sharp tool into the soil. It should push in easily and have moisture along the first 3” or 4”; otherwise, you need to apply more water. Especially hot, dry or windy periods will necessitate increased watering amounts and frequency.
As the turf starts to knit its new roots into the soil, it will be difficult and/or harmful to pull back a corner to check beneath the turf. You can still use a sharp tool, however, to check moisture depth by pushing it through the turf and into the soil. After the sod has become well rooted, you can begin to ease back on irrigation frequency and, instead, follow the tips above.