Fertilizer brings much-needed nutrients to soil. A good fertilizer will control weeds, promote plant growth, and ensure a high-quality soil, allowing you to grow healthy, dense grass for your lawn. Applying fertilizer is an important step in maintaining a healthy and beautiful yard. But timing is everything—otherwise you’re wasting money, or worse, causing environmental damage to your local ecosystem.

Here’s the most important information for learning when and how to fertilize your lawn.

When to fertilize

Don’t overfeed your lawn—fertilizer is expensive, can damage the environment, and won’t necessarily help your grass grow. For most lawns, you’ll need to apply fertilizer only once or twice per year. When planning to apply fertilizer, check the weather report.

The best time to fertilize is the day after a rainstorm—you can simulate with a heavy watering—so the ground is ready and able to absorb the nutrients. The worst time is right before a heavy downpour, as the fertilizer would wash away and potentially cause environmental harm due to runoff in stream systems and tributaries.

However, the key determinant is not based on season—it’s based on the type of grass you’re growing. There are two primary types of grass, and your lawn will be one, the other, or both.

1. Cool-season grasses

These grasses grow best in cooler weather and are common in the northern United States. All cool-season grasses perform best when fertilized between the end of summer and the first frost. Depending on how your lawn fares during winter, you may decide to fertilize lightly in late spring before the rainy season. To determine if this is necessary, give your lawn the look test—if it looks healthy, don’t fertilize. Common cool-season grasses include Kentucky bluegrass, bentgrass, fescue, and ryegrass.

2. Warm-season grasses

These grasses are dormant in the winter. They’re common in the southern United States and other warmer climate zones. It’s best to fertilize in the early summer, as most of their growth occurs during the summer months. You can add another lighter application of fertilizer in the late summer—if your lawn appears to need it. Common warm-season grasses include Bermuda, zoysia, buffalo, and St. Augustine grass.

Which fertilizer is best?

There are dozens of fertilizers on the market. But what is the best fertilizer for your lawn? To determine this, you’ll want to test the soil’s pH with pH strips. These strips are very affordable and can be found in drug stores and online. Test your soil’s pH in less than an hour prior to buying fertilizer for your lawn.

Based on the pH content of your soil, you’ll be able to determine which fertilizers provide the nutrients that your lawn needs to grow and thrive. Armed with the knowledge of your soil’s pH balance—ideally between 6 and 7—you’ll be able to ask staff at your local garden store for a fertilizer recommendation.

How and when to buy fertilizer

There’s one other variable that you’ll need to know in order to maximize your investment in fertilizing your lawn—the square footage of your yard. Fertilizer is often sold by the square foot or by the cubic foot. To determine how much you’ll need, multiply the length of your lawn by its width in feet and subtract any area that’s covered by your home, driveway, or other structures. Plan to purchase 5%–10% more than your estimate.

The best time to buy fertilizer is within a few days of when you plan to use it. You’ll be able to purchase fertilizer from most big-box stores with garden sections, home and garden shops, and even some hardware stores. Depending on your region, you may also be able to buy fertilizer directly from a farmer or supplier—but they may know less about the nutrient content and whether it’s a good fit for your lawn.

How to fertilize your lawn: four common methods

If you prefer to DIY, you won’t need to hire a landscaper to fertilize your lawn. Depending on the size of your lawn and the method of fertilizing you plan to deploy, allow for 2–6 hours to complete the project. Here are the four most common methods for fertilizing a lawn.

1. Broadcast or rotary spreader—This method is most commonly used to fertilize large lawns. Place the spreader in your driveway or on a tarp or other surface to easily collect spills and slowly fill it with fertilizer. Apply the fertilizer evenly to your lawn, starting at the outer edges and then working your way inward. You can either use a criss-crossing pattern or apply in parallel strips, overlapping slightly to make sure all areas are covered.
2. Drop spreader—This method is good for smaller lawns and allows optimal control over fertilizer distribution. Fill the hopper with fertilizer and distribute by walking back and forth in parallel lines.
3. Spray—Only works with liquid fertilizers. To apply a liquid fertilizer, fill the canister with fertilizer and attach the canister to the end of a garden hose. Steadily and evenly walk back and forth on your lawn, spraying the fertilizer on either side of you.
4. Compost—Compost is an environmentally friendly alternative to fertilizer, as it provides nutrients to both grass and soil. Drop and spread compost evenly across the surface of your lawn when you would apply fertilizer—you could use a drop spreader or rotary spreader to do this. You can also use a wheelbarrow, shovel, and rake. Shovel compost into your wheelbarrow, and turn it over on your lawn to make small piles. Use the rake to spread the fertilizer and distribute it evenly.

It’s OK to seek advice on how to fertilize your lawn—either from store employees or a member of a garden cooperative. They’ll be able to help answer questions about which fertilizer is best for your lawn based on your pH content and the type of grass—and how to apply it.

Whatever method you select, spread fertilizer with care. There are environmental considerations and consequences for misapplying fertilizer. After you’re done fertilizing your lawn, rake or collect any fertilizer that remains on hard surfaces like the street, driveway, or sidewalks to prevent fertilizer runoff into water systems.