The Best Time to Apply Fall Fertilizer for a Lush, Green Lawn Next Spring

Here's how and when to give your lawn a nutrient boost before freezing weather hits.

Depending on the type of grass you have and where you live, applying fertilizer to your lawn in the fall can help it come back strong the next spring. The goal is always to add nutrients when grass roots are actively growing. For cool-season grasses such as bluegrass, fescue, or rye grass, the most root growth happens in early fall. For warm-season grasses such as Bermuda grass, zoysia, and St. Augustine, they do better with a fertilizer boost in spring to help fuel summer growth.

This guide explains how to fertilize a cool-season lawn at the ideal time in fall for the most benefit. Plus, find out the best type of fertilizer you should use to support root growth.

When to Fertilize Lawns in Fall

The best time to add fertilizer to your lawn in the fall is during the month of September, unless you live in the southern third of the U.S. That's because the northern two-thirds of the U.S. is home to lawns with cool-season grasses or "transition" lawns with both cool-season and warm-season grasses.

You should also avoid throwing fertilizer on your cool-season lawn in August. During the heat of summer, those grass roots are just biding their time, waiting for the temperatures to go back down. The fertilizer will probably end up washing away before it can do any good.

Best Fertilizer for Cool-Season Grass

When shopping for fertilizer, you'll see the letters N-P-K on fertilizer labels. They stand for the key nutrients: Nitrogen (N), phosphorus (P), and potassium (K). Odds are your soil has plenty of phosphorus and potassium, but nitrogen can get depleted as your grass uses it up.

It's important not to apply unnecessary nutrients to your lawn because excess phosphorous can cause major problems in waterways by causing algae to "bloom" or grow exponentially. An algae bloom throws off the balance of the ecosystem that keeps the water clear and fish and other aquatic life healthy. In fact, in some states it isn't even legal to buy lawn fertilizer with all three key nutrients unless you have a soil test to prove you need them. Other states simply limit phosphorus in lawn fertilizers.

For both the health of the larger ecosystem and for your lawn, go with a slow-release nitrogen fertilizer. The fertilizer bag display of N-P-K should have a bigger number in the first place and either zeros or smaller numbers for the other two nutrients, like 32-0-10.

How to Apply Fall Fertilizer to Lawns

Don't fertilize a dry lawn. Instead, wait until the day after a rain, when the soil is moist. It's also best to time your fertilizer application so there's at least a few days before the next rain so your fertilizer doesn't get washed away before it gets absorbed into the soil.

Follow the label directions for how much fertilizer to apply to your lawn. Use a spreader or broadcaster, walking your lawn in a regular pattern to scatter the fertilizer as evenly as possible. Avoid sidewalks and other hard surfaces as much as possible to avoid waste.