Proper lawn care in fall helps ensure an attractive, healthy lawn next season. Iowa State University Extension and Outreach horticulturists share tips on fall lawn care practices, including controlling broadleaf weeds, mowing, fertilizing and aerating. To have additional questions answered, contact the horticulture hotline at hortline@iastate.edu or call 515-294-3108.


When is the best time to apply a broadleaf herbicide to the lawn?


Fall (late September to early November) is the best time to control perennial broadleaf weeds in the lawn with broadleaf herbicides. In fall, perennial broadleaf weeds are transporting food (carbohydrates) from their foliage to their roots in preparation for winter. Broadleaf herbicides applied in fall will be absorbed by the broadleaf weed’s foliage and transported to the roots along with the carbohydrates, resulting in the destruction of the broadleaf weeds.


Effective broadleaf herbicides include 2,4-D, MCPP, dicamba, triclopyr and others. The most effective broadleaf herbicide products usually contain a mixture of two or three herbicides, as no single compound controls all broadleaf weeds. Broadleaf herbicides can be applied as sprays or granules. (Sprays are generally more effective than granular products in controlling broadleaf weeds.) Before applying any herbicide, carefully read and follow label directions.


lawn mowing by Horticulture/stock.adobe.com.How long should I continue to mow the lawn?


Continue to mow the lawn until the grass stops growing in fall. The foliage of Kentucky bluegrass and other cool-season grasses usually stops growing in late October or early November in Iowa. Mow Kentucky bluegrass lawns at a height of 2½ to 3 inches in fall. When mowing the lawn, never remove more than one-third of the total leaf area at any one time. Accordingly, a lawn being mowed at a height of 3 inches should be cut when it reaches a height of 4½ inches.


When should I fertilize the lawn?


Mid-September and late October/early November (after the grass has stopped growing) are excellent times to fertilize Kentucky bluegrass lawns in Iowa. Mid-September fertilization helps the grass recover from stressful summer weather. An application of fertilizer in late October/early November promotes root growth and early green-up next spring. Apply no more than 1 pound of nitrogen per 1,000 square feet in a single application. Lawns also can be fertilized in spring (April to mid-May).


When should I aerate the lawn?


Early September is an excellent time to aerate lawns growing in heavy, clay soils and those subject to heavy foot traffic. Aeration relieves soil compaction, improves water and nutrient movement in the soil, and prevents thatch accumulation.


Aerate lawns with a core aerator. Core aerators have hollow metal tubes or tines that remove plugs of soil. Remove soil cores that are approximately three-fourths of an inch in diameter and 3 inches in length. When completed, properly aerated lawns should have 20 to 40 holes per square foot. This usually requires several passes of the core aerator. Lawns also can be aerated in April or early May.