When to seed, feed, aerate and clean up: a Pennsylvania lawn and garden calendar

Updated November 10, 2026 · KeystoneProGuide editorial team

What is the short answer?

Most lawn work in Pennsylvania belongs in two windows: mid to late spring, and late summer to early fall. Penn State Extension calls late summer to early fall usually the best time to establish a new lawn from seed, and it is also the preferred time for aeration, dethatching and fall feeding. Mowing runs all season, and some tasks are needed only when a problem calls for them. Penn State bases its calendar on a typical year, and says to delay work in severe drought, heat or cold.

What belongs in spring?

Crabgrass prevention. Penn State says pre-emergence crabgrass control goes down before the weed seed germinates, and gives March 15 to April 15 as the suggested window for southeastern Pennsylvania. It adds that the first step in weed control is a dense, well-managed lawn.

Aeration. Early to mid-spring is one of Penn State's two windows for core aeration, the other being late summer to early fall. It warns that spring aeration can bring weed seeds to the surface.

Feeding. Penn State says most lawns benefit from nitrogen each year, and that this can be met with a fertilizer containing some slow-release nitrogen in mid to late spring, late summer to early fall, or both, at the rate on the label. The state's fertilizer law adds the when-not rules: not before heavy rain, and never on frozen or snow-covered ground.

Seeding. Spring is possible, and Penn State lists mid to late spring among the optimum times. But it says spring seedings face more weeds and must survive their first summer, so late summer remains its preference.

How often should the lawn be mowed?

As often as it grows. Penn State says to mow regularly while the grass is growing, at 2 inches or above, which in a spring flush can mean more than once a week. In drought, the lawn may not need mowing until rain brings growth back. Angi, a cost survey, prices mowing per visit at $50 to $205, so ask how many visits a season contract covers.

What does summer call for?

Mostly restraint. Penn State's calendar says not to dethatch during high temperatures or drought, and that summer seedings face heat, drought and disease. On water, the EPA's WaterSense program says a landscape typically needs about an inch a week including rain, that watering should avoid the middle of the day, and that watering too often produces shallow roots. It also suggests inspecting an irrigation system monthly for leaks and broken heads.

Summer is also insect season. Penn State says chinch bugs and sod webworms do their damage in hot, dry weather from June to August, and Japanese beetle grubs feed on roots in May and June and again from late August to early October.

Why is late summer the busiest window?

Because cool-season grass grows best then. Penn State says seedlings sown in late summer get two cool growing seasons, fall and spring, before their first summer, and that weeds are less of a problem than in spring. It does not suggest seeding later than mid-October in most of the state. The same window suits overseeding, core aeration and, where the thatch is an inch or more deep, dethatching. Penn State says broadleaf weeds such as dandelion are treated while they are actively growing, in spring or early fall.

When should trees, shrubs and perennials go in?

Early to mid fall works well. Penn State Extension says container-grown trees, shrubs and hardy perennials can be planted then, with at least six weeks before the first frost for roots to establish, weekly checks and watering if dry before winter, and mulch to keep them from heaving. Spring bulbs go in during cool fall weather, before the first hard frost. Lime, if a soil test calls for it, is best applied in fall, Penn State says, because winter's rain, snow and freezing help work it into the soil.

What about leaves and mulch?

Penn State's Master Gardeners say not to wait until all the leaves have fallen: mow over them while they are fairly dry and not piled thickly, so they shred into the lawn. In Philadelphia, the city's leaf recycling program runs from early November to mid-December. For mulch, Penn State advises against adding a full new layer each spring; rake the old mulch and add a thin skim.

What about spotted lanternfly?

Penn State says eggs are laid from September to December and hatch from late April to June, with adults active from July until hard freezes. Scrape egg masses in late fall and winter, and set circle traps as soon as the nymphs hatch.

Which tasks are not yearly?

• Dethatching. Penn State says it is not necessary every year, only when thatch builds up to an inch or more.
• Liming. Only on a soil test recommendation.
• Reseeding a whole lawn. Only after finding the cause of decline, as the signs guide explains.

Which of these you take on yourself is covered in doing it yourself or hiring. For prices, see the cost guide, and local businesses are on the landscapers directory page.

Sources

1. Lawn Management through the Seasons, Penn State Extension
2. Lawn Establishment, Penn State Extension
3. Is Fall for Planting?, Penn State Extension
4. Homeowners and Applicators, Pennsylvania Department of Agriculture
5. Watering Tips (WaterSense), U.S. Environmental Protection Agency
6. Spotted Lanternfly Management Guide, Penn State Extension
7. Leaves Are Treasure, Not Trash, Penn State Extension
8. Mulch Volcanoes Are Erupting Everywhere!, Penn State Extension
9. Recycle fall leaves, City of Philadelphia
10. How Much Does Lawn Care Cost? [2026 Data], Angi