When to Fertilize Your Lawn

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Most people fertilize when the garden center fills up with bags in spring. For a lot of lawns, that’s the wrong moment. Grass uses nitrogen best when it’s actively growing roots, and when that happens depends on what kind of grass you have.

I keep this simple on my own lawn: figure out the grass type, then let soil temperature and the calendar decide. The timing below comes from university extension services across the country.

First: what kind of grass do you have?

Everything depends on this.

Cool-season grasses grow most in spring and fall, slow down in summer heat, and stay green into late fall. Tall fescue, Kentucky bluegrass, perennial ryegrass and fine fescues fall here. They cover the North and much of the transition zone.

Warm-season grasses green up in late spring, grow hard in summer and go brown after frost. Bermudagrass, zoysia, St. Augustine and centipede are the common ones in the South.

If you’re not sure, my guide to cool-season vs. warm-season grass shows how to tell.

When to fertilize cool-season grass

Early fall: the main feeding

Fall is when cool-season grass builds roots and stores energy. University of Wisconsin Extension calls Labor Day the optimum time to fertilize lawns in the state, and says early September belongs in every year’s schedule. For low-maintenance lawns, it may be the only feeding all year.

Purdue’s turf program recommends putting 50 to 60% of the year’s nitrogen down between Labor Day and Halloween. Missouri Extension calls September “the most important time to fertilize,” at 1 to 1.5 lb of nitrogen per 1,000 sq ft.

Mid to late fall: a second feeding

Missouri Extension suggests a second fall feeding around mid-October. Purdue’s rule of thumb is to put the spreader away once Halloween has passed. It says growth slows when soil drops below 40°F, so grass can’t use nitrogen well, and you shouldn’t fertilize frozen or dormant turf. If you do feed in November, Purdue says to use a lower rate, because late nitrogen can cause too much growth the next spring.

Spring: light and not too early

Missouri Extension suggests early to mid-April at 0.5 to 1 lb of nitrogen per 1,000 sq ft, preferably slow-release. It also says to stop nitrogen after May 1, especially fast-release forms, because they can encourage leaf disease. Two or three fall feedings can make a spring one unnecessary.

The reason to go light in spring: grass already grows fast then. Heavy spring nitrogen pushes leaves at the expense of roots right before summer stress.

Summer: skip it

Cool-season grass slows down or goes semi-dormant in summer heat. Fertilizing then mostly feeds disease and weeds. Wait for fall.

Cool-season schedule

Annual totals, per Missouri Extension: 3 to 4 lb for tall fescue or ryegrass, 2 to 3 lb for common Kentucky bluegrass, and 4 to 5 lb for high-quality bluegrass. Purdue Extension puts low-maintenance lawns at 1 to 3 lb per year.

When to fertilize warm-season grass

Wait for real green-up

Warm-season grass shouldn’t get nitrogen while it’s still waking up. UGA Extension says to start when soil at 4 inches reaches 65°F or higher. Before that, roots can’t take up the nitrogen well and more of it can leach into groundwater.

Clemson’s Home & Garden Information Center gives a simple rule of thumb: wait until nighttime temperatures are around 70°F. It warns that fertilizing too early pushes shoots at the expense of roots and can increase damage from late frosts. Clemson says most warm-season grasses are actively growing by early to mid-May.

Feed through summer, stop by late summer

UGA Extension’s South Georgia guide gives schedules by grass:

• Bermudagrass: start when soil hits 65°F at 4 inches, typically late April. Feed every 6 to 8 weeks until mid-August. Avoid fall feeding.
• Zoysiagrass: start once fully green, usually late April or early May. Feed every 7 to 8 weeks until mid-August.
• Centipedegrass: fertilize twice, after spring green-up and in midsummer. Skip fall.
• St. Augustinegrass: start when about half the lawn has greened up in late April. Feed based on soil test results and how the grass responds.

Warm-season nitrogen per year

Those totals are from UGA Extension. Split them into smaller feedings over the season instead of one heavy one. UGA’s example is four 1 lb feedings for bermudagrass instead of a single 4 lb dose.

Centipede needs the most care. Clemson says too much nitrogen causes decline and disease in centipede, so stay at the low end.

How much to apply each time

Most extension guides land on the same number: about 1 lb of actual nitrogen per 1,000 sq ft per application. Purdue Extension says not to exceed that with quick-release products. Organic and slow-release products are the stated exception.

To figure out what that means for your bag, multiply the bag weight by the first N-P-K number. A 17 lb bag of 30-0-3 contains about 5 lb of nitrogen, enough for about 5,000 sq ft at 1 lb per 1,000. Most bags list coverage, so check it and set the spreader as the label says. My best lawn spreader guide covers the tools.

Slow-release nitrogen lasts longer between feedings. Missouri Extension says soluble nitrogen is used up in about 3 to 4 weeks, while slow-release lasts about 6 to 8. Lawn products often contain 24 to 50% slow-release nitrogen.

Signs it’s the right moment

• The grass is actively growing. You’re mowing regularly.
• Soil temperature fits your grass. 65°F at 4 inches for warm-season grass. For cool-season grass, fall feeding happens while soil is still well above 40°F.
• No heavy rain forecast. Fertilizer makers like Scotts and Pennington say not to apply before heavy rain.
• The lawn isn’t drought-dormant. Brown, dormant grass can’t use nitrogen. Water first.

Local fertilizer laws

Some states set dates. University of Maryland Extension explains that Maryland law doesn’t allow lawn fertilizer before March 1 or after November 15, and that lawn maintenance fertilizers there must contain zero phosphorus and at least 20% slow-release nitrogen. Some fertilizer labels also have special rates for certain states. Check your state and county rules before buying.

Fertilizer and other lawn jobs

Seeding. New seed benefits from a starter feeding. Pick a product the label says is safe for seeding. See how to overseed a lawn.

Crabgrass preventer. Spring preventers often come combined with fertilizer. That works on northern lawns. AgriLife Extension says Texas lawns should use preventers without nitrogen, because warm-season grass is mostly dormant when crabgrass sprouts. More in how to get rid of crabgrass.

Mowing and watering. Grass that’s fed but scalped or underwatered won’t respond well. The lawn care calendar shows how it all fits together.

Common timing mistakes

Heavy feeding in early spring on cool-season grass. It feels natural when everything turns green, but the grass is already growing fast. Missouri Extension suggests a lighter rate in April and nothing soluble after May 1.

Feeding warm-season grass before it’s green. Clemson and UGA both warn against it. Roots can’t use the nitrogen yet, and new shoots are exposed to late frosts.

Summer feeding on fescue and bluegrass. Grass under heat stress doesn’t need a push. Fall does far more good.

Fall feeding on bermuda or centipede. UGA says to avoid it. Late nitrogen on warm-season grass that’s heading into dormancy doesn’t help winter survival.

Fertilizing dormant or frozen turf. Purdue says to skip it. The nitrogen just sits there or washes away.

Too much at once. Splitting the yearly amount into several smaller feedings works better than one big dose, as UGA’s bermuda example shows.

Example year: tall fescue lawn

Here’s how the extension guidance adds up for a typical tall fescue lawn in the transition zone, using Missouri Extension’s 3 to 4 lb yearly range:

• Early to mid-April: 0.5 to 0.75 lb nitrogen, slow-release.
• Early September: 1 to 1.5 lb nitrogen. Also the time to overseed thin spots.
• Mid-October: about 1 lb nitrogen.
• Early November: a reduced rate only if the grass is still growing and local rules allow.

Example year: bermudagrass lawn

Using UGA Extension’s guidance and 2 to 4 lb yearly range:

• Late April or when soil hits 65°F at 4 inches: first feeding, about 1 lb nitrogen.
• Every 6 to 8 weeks after: about 1 lb nitrogen each time.
• Mid-August: last feeding.
• Fall and winter: none.

Get a soil test

A soil test tells you pH, phosphorus and potassium, which a bag can’t. UGA Extension notes that labs don’t test nitrogen, but they base recommendations on your grass. Your county extension office can send a sample to the state lab. It’s cheap and takes the guessing out of which N-P-K to buy.

What to buy

For most lawns, a zero-phosphorus fertilizer with some slow-release nitrogen covers spring and summer feedings, and a fall product with extra potassium suits the Labor Day feeding on cool-season lawns. My best lawn fertilizer guide compares the options.