When to Aerate Your Lawn: Dates by Grass Type and City

Core-aerate a cool-season lawn (tall fescue, Kentucky bluegrass, ryegrass) in late summer to early fall, with early spring as the second choice. Aerate a warm-season lawn (Bermuda, zoysia, St. Augustine, centipede) from late spring through summer. Either way, aerate while the grass is growing hard, leave it four weeks of good growing weather afterwards, and wait for soil that is moist but not wet.

Below, we turn the extension calendars into dates for 27 US cities using NOAA’s 1991–2020 climate normals, and check them against published local windows.

The best time to aerate, by grass type

Every extension calendar follows one rule: aerate when the grass can heal fast. Kansas State University puts it plainly:

Core aeration can be done anytime the grass is actively growing.

Cool-season grasses grow best when daytime highs run 60–75°F, and warm-season grasses at 80–95°F, according to University of Tennessee Extension and NC State.^4,5 So the two lawn types run on opposite calendars. Not sure which you have? See our guide to cool-season vs. warm-season grass.

Fall wins for cool-season lawns because there is less heat stress and less risk of weedy annuals moving in, says Clemson Extension’s aeration fact sheet.³ Penn State adds that spring aeration can bring weed seeds to the surface.⁸ For Bermuda, Clemson waits until the threat of frost has passed.⁹

Your aeration window, city by city

Months stand in for temperature, so we worked from temperature directly, using two published rules. Warm-season grass grows best once daytime highs reach 80°F. And the lawn needs time to fill the holes: K-State’s Aerating Your Lawn (MF2130) asks for four weeks of good growing weather after aerating warm-season grass,² and Clemson sets the same margin for cool-season lawns:

Allow at least four weeks of good growing weather to help the plants recover.

For each city we took the normal daily high at the nearest NOAA station,¹ found when it crosses 80°F in spring and in fall, and counted back four weeks from the fall crossing.

Where normal July and August highs top 95°F, above the best growing range, aerate early in the window and watch the watering: Clemson warns that aerated turf dries out faster in summer drought.³

The last day for fall aeration on cool-season lawns

For cool-season grass, the end of the window matters most: four weeks before normal highs drop below 60°F, the bottom of the best growing range.⁴ Start once the summer heat breaks; in Fargo, NDSU’s window opens in late August.⁷

Overseeding at the same time? Use whichever comes first: this date or the last safe day to overseed for your area.

How the dates compare with extension calendars

The south Georgia window closely matches UGA’s calendar,⁶ and the start dates line up elsewhere. Our end dates run up to about three weeks later than K-State’s, so treat them as limits, not targets. Coastal stations are the weak spot: Charleston’s downtown station doesn’t reach 80°F normal highs until May 22, yet Clemson says coastal Bermuda lawns usually green up in April.⁹ On the coast, let green-up start your window.

Core or spike aeration?

Use a core (plug) aerator. Its hollow tines pull plugs of soil out, which relieves compaction, lets water and air reach the roots and helps control thatch.² A spike aerator’s solid tines push soil sideways; K-State says the effect is short-term and the soil around each hole is compacted again.² Utah State Extension keeps solid tines for very sandy soil.¹³

Aim for holes about 3 inches deep, 3 inches or less apart and 3/4 inch wide, which usually takes several passes (K-State).² Clemson suggests two passes at right angles.³

Leave the plugs where they fall. Rain, mowing and foot traffic break them up, and they carry microbes that help decompose thatch.^3,7

Check soil moisture first

In dry soil the tines barely penetrate; in wet soil they clog and leave no plugs.² If soil sticks to your shoes or a soil probe, Clemson says to wait for it to dry a little.³ Colorado State Extension suggests watering a dry lawn a couple of days ahead.¹⁴

Moist soil also shows whether you need to aerate at all. Push in a screwdriver: if it slides in easily, you probably don’t; if it is hard to push, the soil is likely compacted.³

How often to aerate

NDSU Extension says almost every lawn benefits from aeration but most do not need it. Lawns with heavy foot traffic, thatch over 1 inch or heavy soils benefit most.⁷

• Most lawns: every 1–5 years (NDSU), or once a year on soils with lighter use (K-State).^7,2
• Clay soil with heavy use: twice a year (K-State); up to 2–4 times a season on poorly drained, heavily used soil (Clemson).^2,3
• Thatch-prone grasses: Bermuda, zoysia and buffalograss need more aeration than bluegrass or fescue (K-State).²

Mark sprinklers and utilities before you start

Related guideWhen to Overseed Your Lawn: The Last Safe Day Where You Live

Aerating with seed, fertilizer and pre-emergent

Seed. NDSU says you can overseed right after aerating, and Colorado State notes that seed in the holes stays moist and protected.^7,14 Clemson differs for sparse areas: make six to ten passes and give the holes about a month to heal first, or new grass comes up mostly in and around the holes.³ For seeding dates, see our overseeding guide or, in the North, our dormant seeding guide.

Fertilizer. K-State advises aerating before fertilizing, seeding or applying crabgrass preventer.² Feeding dates are in our guide on when to fertilize a lawn.

Pre-emergent. Aerate first, then apply it: Clemson and Utah State warn that coring through the herbicide barrier lets weeds through.^3,13 If you have already applied one, Clemson suggests waiting until just before the next application.⁹ Crabgrass preventer also kills seedling grass, Colorado State notes, so follow the label’s waiting period before seeding.¹⁴ Spring dates by city are in when to apply pre-emergent.

More seasonal tasks are in our lawn care guides and seeding section; the methodology page explains how we use NOAA normals.