Homeowners may think of spring and summer as the proper time to fertilize a lawn, but many lawns can benefit from additional fertilization in the fall. Taking the time to fertilize in the off-season will strengthen your plants’ and lawn’s roots, giving them a strong base on which to thrive next spring. We’ll walk you through when and what to fertilize—and what to use.
When To Apply Fertilizer in the Fall
The right time to apply fall fertilizer depends on your climate and the type of grass in your lawn. Homeowners in the South often have warm-season grasses, those in the North may have cool-season grasses, and those across the middle of the country might have a mixture of both. These different types of grasses have different growing seasons, so it’s important to know which you have.
Warm-season grasses like bahiagrass, bermudagrass, and St. Augustine grass go dormant in the winter and begin growing again in late spring. Their growth period continues all summer and into the fall. These grasses can be fertilized throughout the growing season, but the best times are late spring or early summer, with a lighter fertilization in early fall (September). Fertilizing when the weather first begins to cool allows the grass to recover from the hottest months of summer, since even warm-season grass can struggle in the high heat.
Cool-season grasses like tall and fine fescue and Kentucky bluegrass go dormant during the hottest months of the summer. They stop growing and may wilt, but they will recover when the weather turns cooler. These grasses may begin growing in the late winter months, but they will have flowered and finished setting seed by the early summer. Cool-season grasses can tolerate more fertilizer into later fall as they prepare for winter dormancy—September, October, and potentially November. Special winter fertilizer may provide added cold-weather protection; apply it after you mow the grass for the last time for the season.
Choosing the Right NPK Formula for Your Fall Fertilizer
Fertilizer is categorized by its NPK formula, which is represented by three numbers, such as the common 5-10-5. The numbers represent the ratio of the active ingredients in the fertilizer. The first number represents the nitrogen (N) content, which promotes lawn blade and foliage growth. The second number indicates the ratio of phosphorus (P), which helps root growth. The third number shows potassium (K) content, which promotes cell function and absorption of trace elements. Organic fertilizers are generally less concentrated than synthetic fertilizers, so they will have lower numbers. Note that higher numbers don’t equal better fertilizer—the concentration will just determine how much you need to apply.
The right NPK formula often depends on the plant’s growth stage and life cycle. For lawns, this often means a nitrogen-rich fertilizer, since nitrogen does the most to promote leaf and blade growth. However, too much nitrogen can cause grass blades to grow at the expense of a healthy root system. The best way to know what your lawn needs is to perform a soil test. This may not always be necessary, but if your lawn is struggling, testing the soil can help you find what you need to fix it. Regardless, we recommend choosing a slow-release or organic fertilizer for the healthiest, longest-lasting results.
Best Fall Lawn Fertilizers
The best fertilizer to use in the fall depends on whether you have cool- or warm-season grass.
Best Fall Fertilizers for Cool-Season Grasses
You can apply a high-nitrogen fertilizer to cool-season grass in early fall. A formula of 20-8-8 or 24-0-12 are two good options. Always follow the manufacturer’s recommended rate of application. Some people treat weeds and insects at this time, but unless there are signs of trouble or a history of problems, we recommend only applying fertilizer.
Applying fertilizer to cool-season grass at the end of October or early November is even more important. At that time, apply a fertilizer with a formula of 13-25-12. The push of phosphorus will stimulate root growth through November and even into early December, ensuring your lawn will green up quicker in the spring and become more resistant to disease and drought.
Best Fall Fertilizers for Warm-Season Grasses
For warm-season grass, choose a more balanced or phosphorus-heavy fertilizer, since the grass has already done the bulk of its new growth for the year. This will strengthen the roots for the coming winter months. Again, early fall—usually early September, but later in far-southern states like Florida—is the best time for this type of fertilizer in warm climates.
Fall Plant Fertilizer
Don’t use your extra lawn fertilizer on your plants, as they require different ratios of nutrients. For instance, applying high-nitrogen fertilizer to plants may cause them not to flower or fruit. We recommend researching the nutritional needs of individual types of plants. By the fall, perennials are starting to fade but will benefit from 0-20-0 superphosphate fertilizer scattered around the plants at recommended doses and lightly cultivated into the soil. Next spring, you’ll have stronger plants with more flowers.
Tree and Shrub Fertilizer for Fall
Opinions differ on whether trees and shrubs require yearly fertilizer, but most university agricultural programs, like Clemson’s College of Agriculture, only recommend fertilizing if the tree or shrub is growing poorly and you can’t identify a pest- or weather-related reason. Note that fertilizer will only improve growth if the problem is deficient soil nutrients. If you do decide to fertilize trees or shrubs, late fall or early winter is a good time.
We recommend applying 1—3 pounds of slow-release nitrogen per 1,000 square feet of bed and cultivating lightly to compensate. To figure out the exact amount of fertilizer you’ll need, calculate the square footage of your beds and consult with your local garden center. Fertilizing trees in late September and early October will promote root growth.
These nutrients will still be in the soil come spring when plants start to grow. If you have a tree or shrub that does not flower well, a dose of superphosphate will help promote flower growth. However, if the plant is not located in the right spot, no amount of superphosphate will make it flower.
Fall Bulb Fertilizer
Fall is also the time to plant bulbs so that they’ll flower in the spring. We recommend using superphosphate to promote root growth, ensuring strong flowering in the spring. Some people recommend using bone meal when planting bulbs, but it may attract rodents who eat both the bone meal and the bulbs.
Our Conclusion
Fall fertilizing promotes root growth, leading to healthy plants with numerous flowers in the spring. The best time to apply fertilizer—and the type you should apply—depends on your climate and grass species or plant type, which we’ve detailed above. Pay attention to the nutrient needs of your soil and the timing of upcoming frosts to give your lawn the healthiest head start before the winter months.