Hot, dry summer weather can be tough on the cool-season grasses common in Iowa lawns. Good cultural practices in late summer and fall can help revive stressed lawns and create a healthier lawn for the next growing season.
Mowing | Aeration | Seeding & Overseeding | Watering | Fertilizing | Weed Control | Raking & Leaf Removal | More Information
Mowing
In mid to late September, lower the mowing height from 3.0 to 3.5 inches to 2.5 to 3 inches. When mowing the lawn, never remove more than ⅓ of the total leaf area at any one time.
Continue to mow the lawn until the grass stops growing in fall. The foliage of cool-season grasses, such as Kentucky bluegrass, stops growing when daytime high temperatures are consistently below 50 F. In Iowa, bluegrass usually stops growing in late October or early November. Once the foliage stops growing, the lawn mower can be put away for the winter.
Learn more in this publication: Mowing Your Lawn.
Aeration
Early September is the best time to aerate lawns in Iowa. 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. Avoid spike-type devices that simply punch holes (compacting the soil) in the ground.
Remove soil cores that are approximately three-fourths of an inch in diameter and 3 inches long. For best results, aerate lawns when the soil is moist. Avoid aeration when soils are dry or wet. The tubes or tines will not be able to penetrate deeply when the soil is dry and may get plugged with soil when the soil is wet. Lawns that are properly aerated should have 20 to 40 holes per square foot. Since most core aerators won't remove the proper number of holes with a single pass, several passes are often necessary. After aeration, pull a drag mat or weighted piece of fencing material across the lawn to break up the soil cores on the soil surface.
Learn more in this article: Core Aeration of Lawns.
Seeding and Overseeding
Seeding a New Lawn
The best time to establish a lawn from seed is from mid-August to mid-September. Late summer planting has several advantages over spring seeding. The cool-season grasses will germinate quickly in the warm soil of late summer. The warm fall days and cool nights promote rapid turf growth. Also, few weed species germinate in fall so there is little weed competition.
For new lawns, first prepare the soil. At least 4 to 6 inches of good soil are needed to establish a lawn. If necessary, bring in additional topsoil or organic matter. Be sure the topsoil or organic matter is weed-free. Incorporate the additions such as topsoil, organic matter, and fertilizer into the top 6 inches of soil.
To achieve uniform seed distribution, apply the seed with a drop-type seeder. Sow half the seed in one direction. Apply the remaining half at right angles to the first application. After sowing the seed, lightly rake or drag the area. The seed should be covered to a depth of 1/8 to 1/4 inch. While not necessary, you can roll the area lightly to ensure good contact between the seed and soil.
To promote seed germination, mulch the area with clean, weed-free straw. Mulching materials help to conserve soil moisture. They also prevent soil erosion and crusting of the soil surface. Do not apply too much mulch, it may smother the emerging seedlings. Approximately 50 percent of the soil should be visible through the straw. After the initial watering, irrigate the area frequently and lightly. The objective is to keep the seedbed (upper inch of soil) continuously moist. Do not allow the seedbed to dry out during the germination period. This usually requires daily watering during this time.
Learn more in this article: Seeding a New Lawn.
Renovating and Overseeding an Established Lawn
Mid-August through mid-September is the best time to renovate a thin lawn. Sowing grass seed in late summer has several advantages over spring seeding. Cool-season grass seeds germinate quickly in the warm soils of late summer. Once the grass germinates, the warm days and cool nights of fall promote rapid turf growth. Also, there will be less competition from weeds as few weed seeds germinate in late summer and fall.
To reduce the competition from the established turfgrass, mow the lawn at a height of 1½ to 2 inches. Successful overseeding requires good seed-to-soil contact. Core aerators, vertical mowers, and slit seeders can be used to insure good seed-to-soil contact.
After seeding, keep the upper 1 inch of soil moist with frequent, light applications of water. The seeds of most turfgrasses should germinate in 2 to 3 weeks if the seedbed is kept uniformly moist. Gradually reduce the frequency of watering, but water more deeply, when the grass seedlings reach a height of 1 to 2 inches.
Learn more in this article: Overseeding a Lawn.
Watering
Adding additional water is also an important step to consider in the fall. Turfgrass needs about one inch of water a week to continue active growth. Fall can be a dry time of the year and regular watering will be especially important for newly renovated, seeded or sodded areas.
Once temperatures cool down, the lawn can be brought out of summer dormancy by providing water if regular rains are not occurring.
A good way to see if the yard need water is to walk on the yard and see if you leave footprints in the turfgrass. If the turfgrass stands right back up, it does not need any additional water, but if you leave footprints that is a sign that the turfgrass needs water. A little water stress on the turfgrass will actually force the roots deeper into the soil and help during drier times during the growing season.
If you do need to add water, you will want to water deep and infrequently. Try to add all the water in one or two days and then wait for a week until adding more water. This will continue to support the turfgrass while forcing the roots deeper into the soil.
Learn more in this article: Watering Home Lawns.
Fertilization
Mid-September is an excellent time to fertilize lawns. An application of fertilizer in late summer stimulates turfgrass growth and encourages the grass to fill-in thin spots. Apply no more than 1 pound of actual nitrogen per 1,000 square feet.
Learn more in this publication: Lawn Fertilization.
Weed Control
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 contain a mixture of 2 or 3 herbicides as no single compound controls all broadleaf weeds.
Broadleaf herbicides can be applied as liquids or granules. Before applying any herbicide, carefully read and follow label directions.
Learn more in this publication: Weed Control in Home Lawns.
Raking and Leaf Removal
Turfgrass plants utilize light, water, and nutrients to manufacture food. In fall, lawn areas beneath large trees are often completely covered with leaves. The leaf debris prevents the turfgrass plants from manufacturing and storing food prior to winter and can block light causing areas of the lawn to dieback leaving behind patchy areas of dead grass that are unsightly and more prone to weeds.
A layer of leaves where little or no grass is visible will need to be managed. Leaves can be collected by raking, blowing, or using the collection bag on a mower and then removed from the lawn and added to a compost pile or sent to a composting facility.
Gardeners can also manage leaves on the lawn by mowing. Chopping the leaves up with a mulching mower can help return organic matter to the soil, benefitting the lawn, and for most people, it is easier than raking and removing. The leaves must be chopped into pieces small enough to fall down between the blades of grass. When finished, very little leaf debris should be visible. Mowing is best done when the layer of leaves is thin and dry, so mow often throughout the fall. If the leaf layer is thick, mow over an area more than once.