Lawn Maintenance

Most of us have a lawn of some description already established. Proper maintenance practices must be followed to keep the lawn healthy.

The correct mowing height is probably the single most important factor in the formation of healthy turf. Correct height is important because of two opposite growth patterns in grass. On one hand, the taller the grass, the deeper the roots penetrate, tapping into a larger volume of moisture and nutrients. On the other hand, as the height of grass increases, the density of shoots decreases, which can contribute to weed infestation if the mowing height is then lowered. Cut your grass frequently enough so that no more than 1/3 of the grass blade is removed at one mowing. Weekly mowing increases shoot density. Mowing should always be done with a sharp blade. Grass clippings do not require removal unless they present an aesthetic problem. They usually break down quickly, do not contribute to thatch buildup, and actually add nitrogen to the soil.

Lawns require cultivation by aeration and thatching. Aeration removes small cylindrical cores of soil from the lawn, allowing water and air to penetrate. Home lawns usually require aeration only once every two to four years.

Thatching removes the mat of old grass rhizomes at the surface. The mat prevents the penetration of water and fertilizer. Thatching may be done with a thatching rake or machine when the layer exceeds about 1/2 inch.

Apply fertilizer at the proper time and in the appropriate quantities. Look for fertilizers with a 3- 1-2 ratio of nitrogen, phosphate, and potash such as the commonly available ’15-5-10.” Avoid combination fertilizers/weed killers whose application amounts to indiscriminate broadcasting of herbicides whether or not a problem exists.

Soil tests, generally recommended every two or three years, are useful in determining the necessity of fertilization. Excessive fertilization is a waste of resources and can damage plants. Always follow label directions and consult WSU Cooperative Extension publications for general recommendations. Timing is very important. If you only fertilize once in the Puget Sound area, do it in mid-November. Since timing of this application coincides with the start of the rainy season, it is especially important not to over-fertilize as the excess fertilizer may be carried away in stormwater runoff where it can decrease lake clarity and promote excessive algal growth, robbing the water of oxygen. If you fertilize twice, do it in late June and again in November. Such timing encourages strong root systems which can support vigorous top growth through the spring and summer.


Over watering causes runoff, wasted water and sets the stage for lawn problems. Infrequent, long irrigation cycles allow moisture to penetrate, encouraging deep roots and drought resistant plants. Frequent, short cycles encourage shallow roots which are easily stressed.

Our lawns absorb water at a rate of 3/10 inch per hour. Unfortunately, most irrigation systems deliver up to 1 1/2 inches per hour. What the lawn cannot absorb pools in low areas or becomes runoff that can carry pollutants into stormdrains, creeks, rivers, lakes and Puget Sound.

Lawn Watering Guide
Average Depth
in Test Cans
1/8″ 1/4″ 3/8″ 1/2″ 5/8″ 3/4″ 1″ 1 1/8″
Minutes to Water Every
Third Day in Spring
30 15 10 7 1/2 6 5 4 3 1/3
Minutes to Water Every
Third Day in Summer
60 30 20 15 12 10 8 6 2/3
Minutes to Water Every
Third Day in Fall
24 12 8 6 4 3/4 4 3 1/3 2 1/2

Use this chart as a guide. Decrease watering times and frequencies during cool or humid weather. Skip at least one scheduled watering after any substantial rainfall.

*This chart was prepared by the Washington State Nursery and Landscape Association and WSU Cooperative Extension.

Your lawn needs about 1 1/2 inches of water per week. To find out how much water your irrigation system produces, place several flat-bottomed tuna fish or cat food cans around your sprinkler. Turn on your sprinklers for 15 minutes. Measure the amount of water in each can and add the amounts together. Divide this total by the number of cans to find the average amount of water sprinkled in 15 minutes. Refer to the chart on the right and read the number of minutes you should water, every third day.

Finally, water in the morning before 10 a.m. for maximum uptake. Evening watering is an acceptable second choice, while mid-day watering wastes water and can stress plants. Adjust your sprinklers to avoid watering the sidewalk, driveway, or street. Low cost water timers to shut off flow are readily available in garden and hardware stores and will prevent over-watering if you forget to turn off your sprinklers.

The last component in your lawn care maintenance program, pest management, is treated in the previous chapter.

Spare That Shrub – Do Your Part to Control Erosion