The Best Time To Fertilize Your Lawn, According To An Expert

Lawn fertilizer provides the essential nutrients your type of grass needs to grow and thrive. “A well-nourished lawn exhibits increased resilience against various stresses like drought, foot traffic, and environmental challenges,” says Valerie Smith, content strategist at Sod Solutions. When it comes to getting the most out of those nutrients, the timing and frequency of fertilizer applications is important.

The best time to fertilize your lawn is when the grass is actively growing, which differs for cool-season and warm-season grasses. By adjusting when and how often you fertilize, you not only save money but also reduce unintended environmental impacts caused by run-off. Here's how to determine the best time to fertilize your lawn.

What Are Cool-Season And Warm-Season Lawns?

Before fertilizing, determine if you have a cool-season or warm-season lawn (or both). The active growth period for these two classes of turfgrass differs significantly. Cool-season grasses such as fescue, Kentucky bluegrass, and perennial ryegrass develop during the winter and early spring months. They flower and set seed by early summer and often go dormant during the heat of summer, especially in the South.  

Warm-season grasses are dormant in winter and have a flush of growth when spring arrives. They flower and set seed in summer to early fall before the cold weather returns. Warm-season grasses include zoysia, St. Augustine, centipede grass, buffalo grass, and Bermuda grass. These grasses thrive in heat and are the dominant turf type in Southern landscapes, while cool-season grasses flourish in Northern states. There is a broad transition zone across the center of the country where homeowners can grow both types of grass.  

When To Fertilize Your Lawn

The growth periods of cool-season and warm-season grasses help determine the best times of year to fertilize. Here's when you should fertilize your lawn according to your grass type:

Warm-Season Grasses

“Warm-season grasses should be fertilized in late spring, during summer, and in early fall for growth, summer stress tolerance, and winter preparation,” says Smith. Make spring applications about two weeks after green-up to nourish plants as they break winter dormancy. Follow with an early summer fertilization to help plants endure environmental stresses.

It is important to avoid fertilizer applications during periods of excessive heat or drought. Once the heat subsides in late summer or early fall, a final application can be made to help warm-season lawns recover from summer stresses.

Cool-Season Grasses

“Cool-season grasses like Kentucky bluegrass, which go dormant in hot weather, are best fertilized from late summer into fall and in late spring,” says Smith. In the South, cool-season grasses are often grown in shady areas of the landscape or seeded over Bermuda grass for winter color. Overseeding requires some adjustments to the fertilizing schedule. Stop fertilizing the Bermuda grass in early to mid-September, around 30 days prior to seeding cool-season grasses. Wait to fertilize the newly seeded cool-season lawn until two weeks after seedlings emerge.  

How To Avoid Over-Fertilizing

When it comes to lawn fertilization, Smith warns that “more is not better.” Fertilizing your lawn too often can harm the roots as nutrients build up in the soil. It can also encourage pest problems. "Excessive fertilization can lead to fungus issues and increase the likelihood of run-off. Overfeeding your lawn is wasteful economically and harmful environmentally," Smith says.  

“On the other hand, a well-fed lawn gives environmental benefits,” she says. A healthy lawn is better able to sequester carbon and provide other ecological services such as “rainwater purification, mitigation of stormwater runoff, prevention of soil erosion, promotion of microbial health, oxygen production, and air purification.”  

This is why timing and frequency of fertilizer applications are critical. “The best way to limit fertilizer run-off from lawns is to fertilize when the grass is actively growing (not dormant),” says Smith. Most lawns require only two to three fertilizer applications per year. Apply at the recommended rate and
spread fertilizer carefully using a rotary or drop-type spreader. “Clean up any excess fertilizer on pavements to prevent run-off by either sweeping it or blowing it back into the lawn.” It is also a good practice to leave grass clippings on the lawn. As they decompose, the clippings return nutrients back into the soil.

By adjusting the timing and frequency of fertilizer applications, you can maximize the benefits to your lawn while mitigating unintended environmental impacts. The benefits of a healthy lawn extend beyond aesthetics, says Smith, “benefiting soil health, biodiversity, and overall ecological sustainability.”

Tips For Fertilizing

For best results when fertilizing your lawn, you'll want to consider the weather. There are also times when you shouldn't fertilize. Here are some tips to help get the best results from each application:

• Don't fertilize on windy days or before a heavy rain for better control of where the fertilizer is applied.
• Check product instructions to determine when you can water your lawn after applying fertilizer. Some types can be watered right away, while others, such as weed-and-feed types, need a day or two.
• Don't fertilize during a drought. Fertilizer eventually needs water to help it soak into your lawn's soil. You'll need to give the lawn a couple of thorough waterings after fertilizer is applied. If the fertilizer sits on top of the grass for too long, it can scorch it.
• Make sure the ground has warmed to 55ºF for a few days before applying in spring, and apply in the fall before a frost when the ground temperature gets too cold. Dormant grass gets active once temperatures increase, so don't fertilize before then.
• After reseeding your lawn, choose a product specifically designed for this time, often called "starter" fertilizer.