How to Fertilize Your Lawn This Fall for the Lushest, Healthiest Grass in the Spring

Fall is the perfect time to fertilize your lawn. In many regions, autumn is when abundant rainfall and cool weather inspire your lawn to redirect its energy to root development, rather than grass blade growth—a process that guarantees greener and healthier lawns come spring and summer.

Of course, fertilizing the right way is just as important as fertilizing during the right season. Here, we spoke to lawn care experts about how to do it, as well as the best fertilizers to use.

When to Fertilize

September and October are the best months to fertilize your lawn.

This is especially true for cool-season grasses, says Isaac Mertz, lawn expert and regional technical manager of the Carolina region at TruGreen. “Turf-type tall fescue, Kentucky bluegrass, and perennial ryegrass all have their growing seasons in fall, actively growing in cooler weather at 50 to 70 degrees Fahrenheit,” he adds.

For warm-season grasses like Bermuda, zoysia, centipede, and St. Augustine, fall marks their transition into dormancy. During this time, their energy is focused on developing their root system, as opposed to grass blade growth.

If you know your grass is a warmer variety, try to fertilize in early fall, like August or September, says Mertz. Aim for temperatures around 70 degrees Fahrenheit and use a light application of low-nitrogen fertilizer that's still high in potassium. This will help the grass prepare for winter dormancy.

However, moderation is key. “Using too much nitrogen on this variety can push green growth that gets injured by frosts,” he warns.

How to Fertilize

Follow these simple steps for fertilizing your lawn.

1. Choose the right fertilizer. According to Mertz, fertilizer should be matched to the grass type, season, and soil needs. To do this, check the NPK ratio (nitrogen, phosphorus, potassium) and see if this works for your grass variety. Generally speaking, fertilizers that contain more slow-release nitrogen are recommended compared to ones that contain heavy amounts of quick-release nitrogen, he says.
2. Measure your lawn area. Fertilizer rates are given in pounds per 1,000 square feet, Mertz says. Ensure you know the exact size of your lawn to determine the precise amount of fertilizer needed.
3. Set and fill your fertilizer spreader. Broadcast (rotary) spreaders are the recommended option, says Mertz. Drop spreaders should not be used to apply fertilizer. Set the rotary to the manufacturer’s recommended rate.
4. Apply fertilizer evenly. Make sure you walk at a steady pace when spreading the fertilizer.
5. Water if necessary. “Most granular fertilizers need light watering after application to activate nutrients,” says Mertz. Follow the watering instructions on the fertilizer packet. Remember: Liquid fertilizers typically do not require this step, so check the packaging of your liquid fertilizer separately.

Best Fertilizers

There is no right or wrong fertilizer, since different fertilizers are formulated for particular grass varieties and different times of year.

“The best general-purpose fertilizers are the ones that also improve the soil quality,” notes Craig Elworthy, owner and founder of Lawnbright. “These tend to be low on the salt index, and contain a small amount of nitrogen—plus other macro and micronutrients to balance your soil's needs.”

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Common Mistakes

Avoid these mistakes to ensure your grass benefits the most from fertilizing.

Not Watering After Application

Many fertilizers require watering. “One big mistake we see is not watering,” says Elworthy.

Most fertilizers contain synthetic products that will spread into the atmosphere if they’re not immediately watered in, he adds. However, most liquid fertilizers don’t need this step. When in doubt, always follow the instructions on your fertilizer’s packaging as written.

Applying Too Much Nitrogen

Too much nitrogen in the soil creates a flush of tender top growth that’s vulnerable to winter injury and disease.

Fortunately, this mistake is easily avoidable. “Follow the label," says Mertz. "Most fertilizers will recommend applying between 0.5 to 1 pound of nitrogen per thousand square feet." If you still have doubts, try a slow-release fertilizer, which has a larger margin for error.

Not Setting the Fertilizer Spreader

Another major problem is neglecting to use the correct pattern when applying granular fertilizer.

Doing this often results in missing spots or over-applying in certain areas, says Matt Cline, lawn expert and COO of HillSide Lawn Service. “You're left with uneven color in your lawn—this is possibly the biggest mistake that I see when fertilizing in the fall," he adds.