Lawn Aeration and Overseeding in Janesville, WI

What core aeration does

A core aerator pulls small plugs of soil out of the lawn and leaves them on the surface to break down. The holes let air, water and fertilizer reach the roots and give roots room to grow in soil that foot traffic, mowers and clay have packed down.

UW-Madison Extension's recommendation is core aeration in the fall, when there is adequate soil moisture (UW-Madison Extension, aerating and overseeding). Dry, hard ground keeps the tines from pulling clean cores, which is why a day or two after a good rain is the best time.

Overseeding a thin lawn

For a thin lawn, Extension's order is aerate, topdress, then overseed or slit-seed, so the seed lands in loose soil instead of on top of the thatch. Overseeding should be done by early September so the seedlings are established before hard freezes. Heavy clay, compaction and poor drainage have to be fixed first; seed spread on a lawn that stays waterlogged or packed down will not take.

Rock County's deadline

The Wisconsin State Climatology Office puts Rock County's average first freeze at October 12 and the first hard freeze (28 degrees) at October 23, based on 1995 to 2024 (State Climatology Office, Rock County profile). Working backward, seed that goes down in late August or the first days of September gets the six or more weeks it needs. Spring seeding is possible after the average last freeze on April 26, but spring seedlings meet summer heat and crabgrass before their roots are deep, which is why fall wins.

What it costs

ProMatcher's Janesville cost report puts core aeration of a quarter-acre lawn at $43.29 on average, with a range of $38.48 to $48.10 (ProMatcher, Janesville aeration cost). Overseeding adds the seed and the labor, and the price depends on how thin the lawn is and whether it gets topdressed, so it is quoted after a look at the lawn rather than from a table. The full table is on the lawn care cost page.

After the seed goes down

New seed needs the surface kept moist until it germinates, then deeper watering as it fills in. Extension's general rule for an established lawn is about 1 inch of water a week from rain and irrigation together. Hold off on weed control on newly seeded areas, and mow once the new grass is tall enough to reach the normal mowing height. The first fall feeding in the fertilizer program is the one the new grass uses most, and phosphorus is allowed when establishing new grass under Wisconsin law.