When to Apply Winterizer Fertilizer: Dates by City and State Rules

Apply winterizer fertilizer to a cool-season lawn around the last mowing of the year, when the grass is still green but has stopped growing: usually November in the Midwest and Northeast, and always before your state’s cut-off date. Warm-season lawns (Bermuda grass, zoysia, St. Augustine, centipede) should not get late-fall nitrogen at all.

Below, we estimate that date for 17 cities from NOAA climate normals, check it against two extension calendars, and set it against five state rules that can end the season first.

What “winterizer” means on the bag

“Winterizer” is a marketing name for the season’s last feeding, so the bag’s three numbers tell you more than the word does. Illinois Extension describes these products as “typically high in nitrogen and potassium” and counts the late-season feeding of a cool-season lawn as the winterizer.³ The nitrogen is what the grass uses. UW–Madison Extension says the extra potassium is not needed in any significant amount unless a soil test shows a deficiency.⁷

In the South the word means almost the opposite. In 2005, LSU AgCenter horticulturist Tom Koske warned that many winterizers sold in Louisiana were made for northern grasses:⁸

Winterizing cool-season grass is opposite of winterizing our warm-season grasses.

Cool-season lawns: time it to the last mowing, not the first frost

For Kentucky bluegrass, tall fescue and ryegrass, the late feeding goes down after top growth stops but while the leaves are still green. Illinois Extension puts it about a week after the final mowing: late October to early November in northern Illinois, November in central Illinois and late November in southern Illinois.³ K-State Research and Extension in Johnson County, Kansas, says it the simplest way:

The final November fertilization is normally applied about the time of your last mowing.

In Kansas City that is mid-November through Thanksgiving, using about 1 lb of quick-release nitrogen per 1,000 sq ft.⁴ Purdue Extension prefers nearly all water-soluble nitrogen from early October until early December, or until the ground freezes.²

To turn “when growth stops” into a date, we used the same rule as our guide to when to stop mowing: the day the normal daytime high falls below 50°F, which Iowa State Extension gives as the point where bluegrass stops growing.^19,1

*Pennsylvania caps nitrogen rather than banning it. †D.C.’s rule covers people paid to apply fertilizer. For any other ZIP code, look up your frost dates.

In all 17 cities the estimated feeding date falls 9 to 36 days after the median 32°F frost, and in 15 of them after the 28°F hard freeze too. Advice to feed “before the first frost” would move this feeding weeks earlier than the extension calendars do. Purdue’s stop signal is frozen ground, which is not the same thing as a cold night: our explainer on frost vs. freeze covers the difference.

Do the dates match extension calendars?

We checked the estimate in 10 places with a published window. All 10 landed inside it or within five days.

Windows: Illinois Extension³ and K-State Johnson County.⁴ The rule does not fit the dry West. In Denver the normal high stays above 50°F until December 7, but Colorado State Extension’s window ends in early November at lower altitudes.⁶ West of the Plains, use your state’s calendar.

Some extension services now say skip it

Not everyone still recommends a winterizer. Nebraska Extension notes that turf takes in few nutrients in late fall, when nitrogen leaching risk is highest, so:

the recommendation for a heavy late fall application on well-established lawns has ended

If your grass is dark green, healthy and thick, it says, skip it. Young lawns, or lawns that pests damaged in summer, can still get 0.5 lb of quick-release nitrogen per 1,000 sq ft from October 15 to 30 in Nebraska.⁵ Colorado State Extension calls “lawn winterization” nothing magical: feed the bluegrass lawn with nitrogen from late September to early November.⁶ Nebraska adds that returning clippings all season supplies up to 1 lb of nitrogen per 1,000 sq ft. Our lawn fertilizer schedule shows how it fits into the year.

Warm-season lawns: no late-fall nitrogen

Bermuda grass, zoysia, St. Augustine and centipede grass go dormant for winter, and nitrogen late in the season works against that. UGA Extension in Forsyth County, Georgia, says to stop nitrogen by late August or very early September. Feeding later can delay dormancy, expose the grass to frost and freeze injury, and set it up for spring dead spot.¹¹ Texas A&M AgriLife Extension allows a fall feeding but sets the last nitrogen at least six weeks before the expected autumn frost.¹² Our warm-season feeding table turns that into dates for 20 Southern cities. LSU AgCenter adds that skipping fall nitrogen helps limit large patch disease in zoysia and St. Augustine.¹⁰

A “southern” winterizer is low in nitrogen, has little or no phosphorus, and is higher in potassium. If a soil test calls for potassium, LSU names muriate of potash (0-0-60) as one option; excess potassium can burn the grass.⁹ Not sure which kind of grass you have? Our cool-season vs. warm-season grass guide shows how to tell.

State cut-off dates that end the season early

Some states set the last day by law, whatever the grass is doing. We read the rule text for these five:

Sources: 10 V.S.A. § 1266b;¹³ Rutgers on New Jersey’s 2011 fertilizer law;¹⁴ D.C. Code § 8-104.03;¹⁵ New York Environmental Conservation Law § 17-2103, summarized by Cornell Cooperative Extension;¹⁶ and 3 Pa.C.S. § 6813, published by the Pennsylvania Department of Agriculture.^17,18

Set against our NOAA estimate, the law decides in two places. In all 723 New Jersey ZIP codes, lawns are normally still growing on November 15; the median estimate is December 2. In Vermont, 301 of 308 ZIP codes reach the end of growth after October 15. New York’s December 1 date catches only 112 of 2,154 ZIP codes, nearly all in New York City and on Long Island. No Pennsylvania ZIP code reaches December 15.¹

How to apply a late-season feeding

• Read the label first. It sets the rate and spreader setting. Never put down more than 1 lb of quick-release nitrogen per 1,000 sq ft at once; Purdue suggests 0.5–0.75 lb per feeding from October to December.² Our nitrogen math turns that into pounds of product.
• Green grass, unfrozen soil. Purdue says not to fertilize dormant turf or frozen soil.²
• Moist soil, no downpour. Colorado State says to fertilize moist soil, watering a day ahead if it is dry.⁶ Pennsylvania says not to apply if heavy rain is expected.¹⁸ See how much to water your lawn.
• Sweep it off pavement. New York and Pennsylvania law bar fertilizer on driveways and sidewalks.^22,17

Related guideWhen to Fertilize Your Lawn: A Schedule by Grass Type and Climate

Your next step

Mark two dates: your normal end of growth from the table above, and your state’s cut-off. Use whichever comes first. The fertilizing section has the rest of the year, and the methodology page explains our frost dates.