The Twelve-Month Feeding Calendar, Cool-Season and Warm-Season

Every rate is in pounds of actual nitrogen per 1,000 sq ft, not pounds of product. To convert, divide the nitrogen you want by the first number on the bag expressed as a decimal. A 24-0-6 bag delivering 0.75 lb N per 1,000 sq ft means 0.75 divided by 0.24, which is 3.1 lb of product per 1,000 sq ft.

Carrier abbreviations: PCU is polymer-coated urea, SCU is sulfur-coated urea, AS is ammonium sulfate at 21-0-0. Where a row says urea plus PCU, that is a blended bag with roughly half the nitrogen in each form, which is what most quality lawn products actually are.

The conflict column is the point of the exercise. Compatible means the month has no competing operation. Conflict means there is something in that window that will either waste the fertilizer or be wasted by it, and the cell says which.

Built for Kentucky bluegrass and turf-type tall fescue at a high-input 4.0 lb of nitrogen for the year. Fine fescue and low-maintenance lawns want closer to 2.0 to 2.5 lb — drop the May and late-August applications and you land there without restructuring anything.

The shape of that grid is the whole strategy. Spring nitrogen on cool-season turf mostly produces leaf growth you then have to mow, at a time of year when the plant would rather be building roots. Autumn nitrogen goes into crown and root reserves that carry the lawn through the following summer.

If you only fertilize twice a year, make them September and October and skip everything else. That schedule beats an April-and-May-only program by a wide margin on every measure that matters in August.

Built for Bermuda and zoysia at 4.5 lb of nitrogen for the year. St. Augustine sits a little lower at 3 to 4 lb, and centipede is the outlier at 1 to 2 lb — over-feeding centipede is a well-documented way to kill it, so cut every rate below by half and drop two applications if that is what you have.

Everything hangs off green-up in spring and off first frost in autumn, neither of which is a fixed date.

Warm-season turf needs to harden off before cold weather, and late nitrogen keeps it producing tender growth right when it should be storing carbohydrate and thickening cell walls. The rule of thumb that holds across the south is straightforward: last nitrogen application about six weeks before your first expected frost.

Potassium is the exception and goes on later. It improves cold tolerance and does not push growth, which is why the October row above is 0-0-50 and nothing else.

Cool-season turf runs on a different trigger. Its last application is governed by soil temperature rather than frost — you can keep feeding well past the first frost while the 4 in soil temperature is above 45°F and the turf is still green, because roots stay active long after top growth stops. Once that reading drops below 40°F, stop.

Four collisions account for most of the wasted product on home lawns, and none of them announce themselves. The lawn just does slightly worse than it should and nobody knows why.

Pre-emergent and seeding. A pre-emergent herbicide forms a chemical barrier that prevents seed germination without distinguishing between crabgrass and the ryegrass you paid for. That barrier lasts 8 to 12 weeks depending on the active ingredient and rate. If you put down a spring pre-emergent in March, you cannot successfully seed until roughly June, by which point it is the wrong season to be seeding a cool-season lawn anyway. Pick one per window.

Nitrogen and summer disease. Brown patch on tall fescue is strongly encouraged by high nitrogen going into hot humid weather. That is why the cool-season grid has zeros in June and July rather than a light feed — a light feed is still the wrong direction.

Aeration and pre-emergent. Core aeration punches through the chemical barrier a pre-emergent has formed and gives weed seed a clear channel. If you are doing both, aerate first and apply the pre-emergent afterwards, never the other way around.

Weed-and-feed and everything. A combination product forces you to apply a fertilizer rate on the herbicide's calendar, or an herbicide on the fertilizer's calendar. One of the two is always compromised. Separating the jobs costs an extra afternoon and lets both land in the correct window.

The annual totals in the grids are starting points, and there are legitimate reasons to move off them:

• ▸Returning clippings rather than bagging recycles roughly 20 to 30 percent of the nitrogen you apply. If you mulch-mow consistently, take one application out of the year rather than reducing every rate.
• ▸Sandy soils leach nitrogen faster and want more applications at lower rates. Splitting a 1.0 lb application into two 0.5 lb passes two weeks apart is better than one heavy pass on sand.
• ▸Heavy shade lowers the nitrogen requirement substantially. Shaded turf photosynthesizes less and cannot use the nitrogen; feeding it at the sunny rate produces thin, weak growth. Cut shaded areas to about half.
• ▸Irrigation makes higher rates workable and unirrigated lawns should sit at the bottom of the range. Nitrogen without water is the fastest route to burn.
• ▸New sod in its first season wants lighter, more frequent feeding — around 0.5 lb per application until it has knitted down, which usually takes one full growing season.
• ▸A soil test that comes back high in phosphorus means switching to a zero-phosphorus bag for every application in the grid. Excess phosphorus does nothing useful for established turf, and several states restrict it outright.