Seedhead development in home lawns has raised some interesting questions. Two of the most interesting questions have been: "What causes grass to develop so many seedheads?" and "Can a person allow the seedheads to develop and mature to overseed a thin lawn?"
Seedhead production naturally occurs in cool-season turfgrasses, such as Kentucky bluegrass, under long-days and moderately cool temperatures. Long-day refers to 12 hours or more of daylight. Moderately cool temperatures are average daily temperatures of 65 to 75 degrees. The moderately cool temperatures of the past several weeks have lead to seedhead development in lawns. The dry weather in many areas of the state has accentuated seedhead development. Seedhead development is also greater in those lawns that receive little or no nitrogen fertilizer. The presence of high nitrogen levels delays plant maturation and reduces seedhead formation.
When seedheads are allowed to mature in lawns, they do so at the expense of the lawn's health. The production of seeds requires carbohydrates. These carbohydrates are derived from other plant parts, such as the crown and rhizome. These two plant parts are important in the recovery from summer dormancy. The turfgrass plant regenerates new plants from buds on the crown and from nodes on the rhizome. This regeneration is important when the plant is injured by drought, high-temperature stress, insects, or any other type of injury to the turf. Therefore, if the plant utilizes most of the carbohydrates for seed production, it will be done at the expense of the crown and rhizome and ultimately the health of the plant.
Lawns that have been allowed to grow tall and form seedheads should be mowed as soon as possible. Set the blade as high as possible, then gradually reduce the height of the grass in later mowings. The recommended cutting height for bluegrass lawns during the summer months is approximately 3 inches.
If standard lawn maintenance practices, such as fertilization and proper mowing, don't improve the quality of the turf, home gardeners should renovate their lawn in late summer or early fall. Also, the factors responsible for the thinning of the lawn should be identified and corrected prior to renovation.
This article originally appeared in the June 3, 1992 issue, p. 87.