AMES, Iowa – In late summer and early fall, Iowa has many chores that will help the lawn grow well. Most of Iowa’s lawns are Kentucky bluegrass and other cool-season grasses.

Proper mowing, overseeding, aerating, weeding, and fertilizing late in the growing season can promote lush, green, good-looking lawns in the cooler season. In this month’s Yard and Garden, Aaron Steil, Consumer Horticulture Specialist at Iowa State University Extension and Outreach, offers late summer lawn care advice.

What are the best mowing methods for autumn?

During the stressful, hot summer months, the lawn is mowed at a height of 3 to 3.5 inches. The cooler temperatures in autumn encourage better growth. In September, lower the mowing height to 2.5 to 3 inches. Keep mowing the lawn until the grass stops growing in late October / early November. When mowing the lawn, never remove more than a third of the entire leaf area at one time.

How can I reseed my thin and barren lawn?

Mid-August to mid-September is the best time to renovate a thin lawn. Sowing grass seeds in late summer has several advantages over spring sowing. Cool season grass seeds germinate quickly in the warm soils of late summer. Once the grass germinates, the warm days and cool nights in autumn encourage rapid lawn growth. There will also be less competition from weeds as few weed seeds germinate in late summer and autumn.

To reduce competition from the established lawn, mow the lawn to a height of 2.0 to 2.5 inches before sowing. Successful reseeding requires good seed-soil contact. Core aerators, vertical mowers and slot seed drills can be used for good seed-soil contact.

After sowing, keep the top 1 inch of the soil moist with frequent, light applications of water. The seeds of most lawn grasses should germinate in two to three weeks if the seedbed is kept evenly moist. Gradually reduce the frequency of watering, but watering deeper when the grass seedlings reach 1 to 2 inches in height.

Why and how should I aerate my lawn?

Early September is the best time to aerate Iowa lawns. Aeration relieves soil compaction, improves the movement of water and nutrients in the soil and prevents the accumulation of straw.

Aerate the lawn with a core aerator. Core aerators have hollow metal tubes or tines that remove earth plugs. Avoid point-like devices that simply punch holes in the ground (compact the soil). Core aerators can be rented from hardware stores or machine rentals, or the service can be provided by a professional lawn care company.

Remove cores about three quarters of an inch in diameter and three inches in length. For best results, aerate the lawn when the soil is damp. Avoid ventilation when the floors are dry or wet. The pipes or tines cannot penetrate deeply in dry soil and can become clogged with soil in wet soil. Lawns that are properly ventilated should have 20 to 40 holes per square foot. Since most core aerators do not remove the correct number of holes in a single pass, multiple passes are often required. After ventilation, pull a tow mat or weighted piece of fence material over the lawn to break up the soil cores on the soil surface. If the lawn is smaller, use a stiff rake to break up the earth’s cores.

When and how should I use herbicides for weed control on my lawn?

In small areas, some weeds can be controlled by pulling and digging. This method is best done after a soaked rain or deep watering. Unfortunately, pulling and digging for deeply rooted weeds is often ineffective.

In many situations, herbicides are the only viable weed control method. Perennial broadleaf weeds such as dandelion, clover, thistle, and plantain are best controlled with a herbicide application in Iowa in late September through early November. Effective foliage herbicides include 2,4-D, MCPP, MCPA, Dicamba, Triclopyr, and others. The most effective herbicide products for broadleaf weeds contain a mixture of two or three herbicides, as no single compound will control all broadleaf weeds. Broad-leaved herbicides can be applied as liquids or granules. Do not apply herbicides to newly sown lawns until the new grass has been cut at least twice. Herbicides must be used according to the instructions on the label on the package.

Perennial grass-like weeds such as quack grass and fescue have few options for selective control. When hand digging or pulling is not practical, the most effective herbicide option is the non-selective herbicide glyphosate (Roundup). Nonselective herbicides kill virtually all plants (both desirable and herbaceous) to which the material is applied. Treat the herbaceous perennial grasses on site. More than one application may be required to kill difficult-to-control weeds. Always apply herbicides when the wind is calm and temperatures are cool to prevent drifting and damage to desired plants.

While perennial weeds are best controlled in autumn, annual broadleaf and grassy weeds such as crabgrass and knotweed are best controlled in spring with a pre-emergent herbicide.

When should I fertilize my lawn?

Fertilizer applications can be made in mid-September and late October / early November. Fertilizing in mid-September promotes moderate shoot growth and helps thicken the lawn. Fertilization at the end of October / beginning of November (at the time of the last mowing) promotes root growth and early greening in the following spring. Apply 1 pound of actual nitrogen per 1,000 square feet with each application using a slow release fertilizer.

A single application at the end of October / beginning of November is sufficient for low-maintenance lawns. High maintenance lawns can have a third application of the same amount in spring (April or May).

Divisible photo: Falling lawn.