At this time of year, many homeowners are asking about crabgrass control and basic lawn care. Is it too late to apply crabgrass preventer? When should I fertilize? How often should I be irrigating?
First, determine if the offending grass is truly crabgrass? Many homeowners think they have a crabgrass problem, but what they actually have is a Bermuda grass problem.
Crabgrass is an annual that comes up from seed each year and dies with frost in the fall. Bermuda grass is a perennial that comes back from its tough, wiry trailing stems and rhizomes (underground stems) each year. Its leaves are blue-gray in color, where crabgrass leaves are green. While not similar in appearance, these two grasses often are confused with each other because they have similar seed heads.
Best management practices for a healthy lawn: Your first line of defense against crabgrass should be encouraging healthy, dense turf using good cultural practices. This includes mowing, fertilizing and irrigating properly. Mow bluegrass and bluegrass-mix lawns to a recommended height of 2 to 2.5 inches. A dense, tall turf shades germinating crabgrass seedlings and deters their growth.
Equally important in controlling crabgrass is fertilizing at the correct times of the year to promote root and side growth (called tillering) instead of top growth. The most important time to fertilize your lawn is in the fall. Washington State University recommends making a fertilizer application in early September and again after the last mowing (around mid-November) but before the soil freezes. If you apply fertilizer in the fall, wait until early May to fertilize again. Fertilizing earlier in the spring encourages top growth at the expense of root and side growth, resulting in weaker turf and more frequent mowing. The best times to fertilize lawns in our region are: Nov. 15, May 1, June 15 and Sept. 1, applying 1 pound of nitrogen per 1,000 square feet of lawn area.
When irrigating lawns, the tendency in our region is to water daily starting early in the season for 15 minutes each day. This daily, light irrigation leads to weaker, shallow-rooted, thin turf and makes it easy for crabgrass to germinate and grow. You will have to water more frequently during the hottest part of summer, but during the relatively cool weather of spring and fall you should not be watering daily. Adjust your timers to water less frequently but more deeply to promote deeper grass roots.
Chemical crabgrass control: There are a number of home garden products often called crabgrass preventers that contain herbicides that are applied in the spring before crabgrass seeds germinate to prevent them from sprouting and growing. The general time to apply these products is when the soil temperature reaches about 62 degrees at a depth of 1 to 2 inches or about two weeks after forsythia blooms start to drop.
There are also some home garden products (containing dithiopyr or fenoxaprop) that will kill young crabgrass seedlings after the seeds germinate, although their effectiveness is not as reliable as good turf management and the use of preventer products.
-- Marianne C. Ophardt is a horticulturist for Washington State University Benton County Extension.