AMES, Iowa - Spring has finally sprung across Iowa, and with it, growing green grass on lawns everywhere. The hum of lawn mowers is beginning to fill the air, and that hum brings questions about proper mowing practices.
How should mowing practices be tailored to specific grasses? Iowa State University Extension and Outreach horticulturists can help make lawn mowing rewarding and fruitful.
When mowing the lawn, what is the proper mowing height?
Kentucky bluegrass lawns should be mowed at a height of 2½ to 3 inches in the spring and fall months. Mow bluegrass lawns at a height of 3 to 3½ inches in June, July and August. A higher mowing height in summer helps to cool the crowns of the turfgrass plants, encourages deeper rooting and provides more leaf area for photosynthesis during the stressful summer months.
Mowing below the recommended range may scalp the turf and cause the turfgrass to deteriorate. Extremely low mowing heights decrease the total leaf surface area, carbohydrate reserves and root growth, creating a situation where the turfgrass plants are unable to produce enough food to meet their needs. This makes the plants more susceptible to drought, high temperature and wear injury. In addition, the bare areas created by a decrease in turfgrass density increase the likelihood of weed problems.
Mowing too high also can create problems. Mowing above the recommended range reduces tillering and causes matting of the grass. Reduced tillering results in fewer and coarser plants, while matted grass creates a micro-environment that encourages disease development.
How often should I mow my lawn?
Mowing frequency is based on the growth rate of the turfgrass. Weather conditions, cultural practices (such as fertilization and irrigation practices), and other factors determine the growth rate of turfgrass.
Kentucky bluegrass and other cool-season grasses grow quickly in spring when weather conditions are favorable. The growth of cool-season grasses slows during the stressful summer months and then picks up again in fall. Fertilizing and irrigating the lawn promote turfgrass growth. The faster the growth rate of the grass, the more frequent the mowing.
Mowing height also affects mowing frequency. When mowing the lawn, the general rule is to remove no more than 1/3 of the total leaf surface at any one mowing. A lawn being mowed at a height of 2 inches should be cut when it reaches 3 inches in height, while a lawn being mowed at a height of 3 inches should be cut when it reaches the height of 4½ inches. A shorter mowing height requires more frequent mowing, as a lawn can be allowed to grow 1 inch when the mowing height is 2 inches and 1½ inches when the mowing height is 3 inches.
Should I remove the grass clippings when mowing the lawn?
When the lawn is mowed properly, grass clippings do not need to be removed or bagged. Small clippings filter down into the turf and quickly decompose, returning essential plant nutrients to the soil. Lawn clippings do not significantly contribute to thatch development.
Grass clippings may need to be bagged or raked and removed when mowing extremely tall grass. You may also want to bag the grass clippings and use them as a mulch in vegetable and flower gardens.