# Lawn care calendar for Wisconsin: when to fertilize and seed

> Wisconsin lawn calendar for Kentucky bluegrass and fescues: UW-Madison Extension timing, early September feeding, the state phosphorus law and NOAA frost dates.

Canonical: https://lucernel.com/guides/lawn-care-calendar/wisconsin
Last updated: 2026-10-23

Wisconsin lawns are mostly Kentucky bluegrass, and the UW-Madison Extension calendar leans hard on a short window: late August into early September for seeding and nitrogen. The state also has a phosphorus law for turf, in force since 2009.

**Seed from late August into early September, and feed once on September 1 to 15 with about 1 pound of nitrogen.** UW-Madison Extension says the very late August to early September window is the best time to seed, and that early fall, September 1 to 15, is a key time to feed every lawn in Wisconsin, at about 1 pound of controlled-release nitrogen per 1,000 square feet. Spring feeding waits for the second mowing, and fall nitrogen later than that is avoided because it feeds snow mold and vole damage. Wisconsin law bars phosphorus on turf unless you are establishing grass or a soil test shows a deficiency. (UW-Madison Extension; Wis. Stat. 94.643)

| Month | Cool-season lawn (Kentucky bluegrass, ryegrass, tall fescue, fine fescue) |
| --- | --- |
| January | No fertilizer on frozen ground |
| February | No fertilizer on frozen ground |
| March | Wait for soil to thaw; forsythia blooms from late March |
| April | Rake debris, check for snow mold and vole damage; seed from late April if needed |
| May | Fertilize at the second mowing, about 1 lb N; pre-emergent only if crabgrass history, at 60 F soil |
| June | Mow at about 3 inches; decide whether to water or let the lawn go dormant |
| July | About 1 inch of water a week to stay green; nitrogen under 1 lb on irrigated lawns, if at all |
| August | Scout for grubs; late August is time to prepare the seedbed |
| September | Seed in very late August to early September; feed September 1 to 15; core aerate |
| October | Treat broadleaf weeds early to mid fall; skip mid-fall nitrogen; keep mowing |
| November | Clear leaves before snow; dormant seeding is not suggested |
| December | No fertilizer on frozen ground |

Spring conditions vary considerably from south to north; thaw timing sets the real start.

## Which grasses grow where in Wisconsin

UW-Madison's calendar is for cool-season turf: Kentucky bluegrass, perennial ryegrass, tall fescue and fine fescues. Kentucky bluegrass, the dominant Wisconsin lawn grass, survives weeks of drought by browning and going dormant, though dormant lawns do not tolerate traffic.

Mow at about 3 inches all season, do not make the first spring cut very short, and return clippings, which recycle nitrogen and do not cause thatch. Never remove more than a third of the blade, and set the mower to its highest setting before summer.

## Frost dates from NOAA

Dates are the NOAA 1991-2020 normals for the last spring and first fall 32 F freeze at 50% probability. Milwaukee Mitchell International averages April 19 and October 29. Madison averages May 1 and October 10, and Green Bay averages April 30 and October 9.

Our arithmetic: Milwaukee has about 193 days between those dates, Madison about 162 and Green Bay about 163. Milwaukee has roughly a month more than Madison or Green Bay.

## Spring

UW-Madison says to avoid starting lawn work too early and to pay attention to soil thawing. Rake off debris, then look at the damage: spiraling trails mean voles, matted circular patches mean snow mold, and bleached irregular areas come from winter cold, wind and ice. Reseed as needed.

Wait until the second mowing to fertilize, with about 1 pound of controlled-release nitrogen per 1,000 square feet for a lawn in full sun and less in shade. Feeding at first thaw drives top growth at the expense of roots. If crabgrass was a problem last year, apply a pre-emergent when soil has been near 60 F for several days; forsythia in bloom, from late March to mid-April or later, is the reminder. If not, skip it, and do not use one where you will reseed the same spring. Seed in late April to early May if you must seed in spring, and core aerate with 15 to 20 cores per square foot if the soil is compacted.

## Summer

Decide before dry weather whether to water all summer or let the lawn go dormant. If you water, about 1 inch a week keeps it green, applied early in the day and evenly, and split in two on heavy clay or slopes. Do not wait until the lawn is brown and then try to turn it green, which drains reserves.

Summer nitrogen goes only on irrigated lawns, at less than 1 pound per 1,000 square feet and in controlled-release form, and most lawns do not need it. Avoid vertical mowers, power rakes and seeding in summer, because cool-season grass recovers slowly and crabgrass moves into the open soil. Check for white grubs where brown meets green before treating anything.

## Fall

September is the key month. Late August into early September is the ideal time to seed, sod and renovate, and UW-Madison suggests slit seeding for thin lawns. September 1 to 15 is the time to feed every lawn, about 1 pound of controlled-release nitrogen per 1,000 square feet, and mid-fall nitrogen is skipped to avoid growth surges that invite snow mold and voles. Fall is also good for core aeration and for spot-treating dandelions and other perennial broadleaf weeds while they are growing.

Keep mowing until the lawn goes dormant but do not let it go into winter tall, and clean leaves and debris off before snowfall. Dormant seeding in very late fall is not suggested in most cases.

## Wisconsin's phosphorus law

Section 94.643 of the Wisconsin Statutes says no person may intentionally apply fertilizer labeled as containing phosphorus or available phosphate to turf. Exceptions are applying it to establish grass from seed or sod during the same growing season, and applying it where a laboratory soil test taken within the last 36 months shows a phosphorus deficiency. Nobody may apply fertilizer, manipulated manure or sewage sludge product to frozen ground, or intentionally to pavement.

A first violation carries a forfeiture of up to $50, and later ones $200 to $500. Retailers may not display phosphorus turf fertilizer. The lawn fertilizer calculator on this site works from the nitrogen figure on the bag, which is what UW-Madison's rates are written in.

## Frequently asked questions

### When should I fertilize my lawn in Wisconsin?

September 1 to 15 is the key time, at about 1 pound of controlled-release nitrogen per 1,000 square feet. A spring feeding waits until the second mowing, and mid-fall nitrogen is avoided.

### When is the best time to seed grass in Wisconsin?

Very late August into early September. Late April to early May is the spring option.

### Can I use fertilizer with phosphorus on my Wisconsin lawn?

Only to establish grass during the same growing season or where a soil test within 36 months shows a deficiency.

### How tall should I mow a Wisconsin lawn?

About 3 inches for the whole season, with clippings returned and no more than a third of the blade removed.

### Can Lawnzo help me follow a Wisconsin lawn schedule?

Lawnzo, a planner for iPhone, covers several lawns, each with its own area, grass, exposure and irrigation. It keeps, delays or skips jobs by the forecast and shows the reason, and it can send reminders rebuilt from the current plan.

## Sources (checked 2026-10-02)

- [UW-Madison Extension, Wisconsin Lawn Care Calendar (Spangenberg, 2025)](https://hort.extension.wisc.edu/articles/wisconsin-lawn-care-calender/)
- [Wisconsin Statutes, section 94.643: Restrictions on the use and sale of fertilizer containing phosphorus](https://docs.legis.wisconsin.gov/document/statutes/94.643)
- [NOAA NCEI 1991-2020 normals: frost dates for Milwaukee Mitchell International Airport, Madison Dane County Regional Airport, Green Bay (API query)](https://www.ncei.noaa.gov/access/services/data/v1?dataset=normals-annualseasonal-1991-2020&stations=USW00014839,USW00014837,USW00014898&dataTypes=ANN-TMIN-PRBLST-T32FP50,ANN-TMIN-PRBFST-T32FP50&format=json)
- [NOAA NCEI, U.S. Climate Normals 1991-2020 (product page)](https://www.ncei.noaa.gov/products/land-based-station/us-climate-normals)
- [NOAA NCEI, station inventory (GHCN-Daily station list)](https://www.ncei.noaa.gov/pub/data/ghcn/daily/ghcnd-stations.txt)