Should you aerate, overseed or verticut? Warm soils, cool nights mean lawn care

Early September is the perfect time to overseed a bluegrass and tall fescue lawn. The combination of warm soils and cooler nights create the right conditions for quick germination and establishment of new seed. Soil preparation, seed selection, fertilization and irrigation are essential steps for success.

Prepare the soil by core aeration or verticutting to break the soil crust. Begin by mowing the grass short to about 1 to 1.5 inches. Follow the mowing by verticutting the lawn in one or two directions. Verticutting slices grooves, creating an area for grass seed to fall. This method is preferred for overseeding as it provides an even seedbed.

Remove any debris from the lawn for good seed-to-soil contact. Use a core aerator to break up compacted soil and keep thatch in check. Unfortunately, the core aerator does not provide a uniform seedbed for overseeding.

Avoid inexpensive seed mixes containing species such as creeping red fescue, fine leaf fescue, perennial, annual rye and annual bluegrass. These species may sprout quickly after seeding, but they fail under stressful summer conditions.

Check the seed label to ensure it includes varieties of bluegrass or tall fescue. No other grass species will tolerate our local conditions in the Kansas City area. Bags of grass seed sold nationwide contain inferior species.

Apply the seed at half the seeding rate used for a new lawn. For tall fescue, the standard rate is 6 to 8 pounds per 1,000 square feet. The overseeding rate is 3 to 4 pounds per 1,000 square feet. Broadcast the seed over the prepared area.

The new lawn rate for bluegrass is 3 to 4 pounds per 1,000 square feet, making the overseeding rate around 2 pounds. Bare soil areas may require the new lawn rate. Fescue germinates in about 10 days, where bluegrass may take up to two weeks.

Fertilizer is necessary for new seedlings to establish quickly. Existing grass also benefits from a September fertilizer application.

Unlike the standard grass fertilizer high in nitrogen, fertilize new seed with a balanced fertilizer, such as 13-13-13, or a high phosphorus product, such as 10-20-10. Phosphorus is a macronutrient aiding in the root development of young seedlings.

Fertilizer should be applied at the rate suggested by a soil test, available through your local extension office, or a starter fertilizer should be used at the rates on the bag.

In my experience, most people do not apply enough fertilizer when seeding a lawn as they are afraid of burning the new grass. The opposite typically happens as there is a lack of nutrition and the seedlings fail to grow.

About four weeks after germination, apply a high nitrogen fertilizer with numbers like 27-3-3 or 30-0-0. Repeat this application in mid-November resulting in an early spring green lawn.

Apply water frequently to keep the seedbed constantly moist, ensuring good germination. The new seedlings require frequent, light irrigation as the surface dries out quickly. As the grass germinates and the seedlings establish, progress to deeper more infrequent watering.

The ideal timeframe to overseed your lawn is brief. You will experience exceptional success planting the seed by Sept. 20. Only lawns that are thin or have bare spots require overseeding. If you have a thick lawn, this fall practice can be skipped.

Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Have a question for him or other university extension experts? Email them to garden.help@jocogov.org.

This story was originally published September 3, 2021 at 5:00 AM.