Lawn Care Now for a Dry Summer Ahead
By Dr. Gwen Stahnke
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Mary Robson (Ret.) Area Extension Agent
Regional Garden Column April 13, 2001
Thanks to Dr. Gwen Stahnke, Turf Agronomist, Washington State University WSU Extension, Puyallup, for material used in this column. For more information contact Dr. Stahnke's web page: www.puyallup.wsu.edu/turf Dr. Stahnke is a turf specialist for Washington State University and has studied lawn conditions and taught turf management in Washington state for over 10 years.
How shall we best care for lawns now and through the summer? Do note that some actions depend on whether or not water will be available for summer irrigation. Water availability will vary from district to district and it's important to check with and listen to your local water purveyor about water supplies as the summer progresses. These lawn tips refer to the care of an existing lawn, not to the installation of a new one.
*Thatching:
Check the lawn for the depth of thatch in April. If the thatch depth is greater than 1/2 inch, dethatch the lawn to increase water penetration. If thatch is 1/2 inch or less, do not dethatch. Thatch builds up at the root and crown of the turf grass, and consists of dead grass stems, grass blades, and roots. It's an intermingled layer of living and dead material, with living crowns of grass within the thatch. Thick layers of thatch, once dried out, tend to repel water and keep rain or irrigation from getting down into the turf roots where it's needed. Thatch is not caused by "grasscycling," the return of small cut clippings from mowing. Proper "grasscycling" on perennial ryegrass and ryegrass mix lawns produces clippings that break down rapidly and can return nitrogen to the grass roots.
*Aeration:
Check the lawn for soil compaction in April. If the grass roots are shallow due to traffic on the area, aerate the lawn (pull soil cores). Make sure the soil is moist before you aerate in order to get better penetration of the equipment tines. Aeration will help get oxygen and water down into the rootzone to help develop a stronger root system for the grass. Aerating should be completed in spring for best results when the lawn grows in summer. Do not attempt to aerate a dormant lawn on dry soils during the summer. If you choose not to aerate now, consider it as a fall renovation technique once rains return.
*Overseeding:
If lawn coverage is thin, it is a good idea to overseed (put out turfgrass seed at about 1/2 the normal establishment rate, i.e. for a perennial ryegrass lawn, overseed at 3 lbs seed per 1000 square feet), after thatching or aerating the lawn, to fill in the gaps and prevent weed invasion.
Bentgrass lawns should fill in via stolons, which are above ground lateral stems, and should not need overseeding in most cases.
If you plan to allow the lawn to go totally dormant in the summer, do not overseed until fall when rains have returned.
Newly seeded grass plants and perennial ryegrass lawns on sandy soils will require some moisture in the soil throughout the summer to survive. Water levels in the fall may be even lower and it is a critical time for salmon to use water as well. It may be even less feasible to overseed in the fall due to water levels, even though this is the best time to establish cool season grass plants. If you fill in the gaps in the spring, you should have fewer weeds in the lawn for the growing season.
*Fertilizing:
When fertilizing in April/May, apply only 1/2 pound of quickly available nitrogen per 1000 square feet of turf, in order to prevent lush growth of the grass.
A fertilizer with at least 50% to 70% slow-release nitrogen is a good choice. If soil temperatures are cool, an organic source of nitrogen will not be available to the plant for immediate use.
If any fertilizer hits a hard surface (such as a driveway), be sure to sweep it up into the lawn or landscape or it will become a non-point source of pollution when we irrigate or it rains.
If fertilizing in June, use a slow-release or organic source of nitrogen to limit growth but to provide a source of food when irrigation or rain is available. Do not fertilize established lawns in the summer (July or August).
*Weed control:
If weeds are a problem, control is best in spring or fall. Depending upon the weed species, it could be pulled or spot treated with the appropriate herbicide in spring. The weed should be identified in order to select the best time for control. Washington State University specialists do not recommend use of Weed/Feed lawn products except where weed infestation is severe. This type of combined product should only be applied once a year. If weed infestation is not severe, which is in many cases, it is better to separate weed control from the fertilization. Read all labels on pesticides before buying, applying, storing, or disposing of the material.
*Mowing:
Mow perennial ryegrass and perennial ryegrass mixture lawns at 2 inches maximum height. Bentgrass lawns should be moved no higher than 1 inch to prevent thatch buildup. Return clippings to the lawn to increase nutrients available to the turfgrass plants, as well as limiting evaporation from the soil surface. A thick, dense lawn will shade the soil and limit water loss.
*Irrigation:
If you decide to let the lawn go totally dormant, do not begin watering the grass in midsummer and revive the grass, then turn the water off again. This will damage the grass. Bentgrass lawns can go totally dormant and recover in the fall.
Perennial ryegrass lawns will need to have some moisture in the soil to keep the grass from severely thinning out.
Traffic should be eliminated on dormant grass.
Irrigate in the early morning. Your water district may have to modify this according to the demand for water at that time. Late evening watering is also a possibility. Turn off water immediately if it begins to run off the lawn.
Irrigate to a 4 to 6 inch depth as needed, using publish evapotranspiration (ET) rates from your local water district. Only 80% of ET should be applied to the lawn, and only three times per week maximum at the hottest part of the summer. (One inch of water per week.)
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