The Best Fall Fertilizers for Lawn
A healthy lawn at the start of lawn season begins in the fall. Fall is the most important time to fertilize, especially for cool-season grasses. Cool-season grasses include Kentucky bluegrass, tall fescue, fine fescue, and Perennial ryegrass, to name a few. Choosing and applying the right fall fertilizer will help grass prepare for winter dormancy and a stronger lawn come springtime.
Choosing the Right Fall Lawn Fertilizer
The first thing you should do is conduct a soil test, especially if you have not already done so this year. A soil test will tell you your soil’s nutrient levels and what is missing that should be replenished. You can purchase a soil test from your local garden center, online, or obtain one from your local cooperative extension office.
Once you know your soil’s nutrient levels, you can choose a fertilizer accordingly. If your soil is low on Phosphorus, apply a Phosphate lawn fertilizer, like our 6-18-0 Growth Booster. If your soil is low on Potassium, apply our High Potash fertilizer 0-0-25. If you need to address both Phosphorus and Potassium deficiencies, you can apply High-phosphorus and Potassium fertilizer 3-18-18. If applying Phosphorus, be aware that certain states restrict phosphate applications unless you are establishing a new lawn or can show a phosphorus deficiency.
If you have cool-season grass, early fall is a great time to get Nitrogen applications in. Choose a Nitrogen fertilizer with Potassium to support winter hardiness.
Fall Grass Fertilizer Nutrient Breakdown
Fertilizers are comprised of three macro nutrients, and can also include micro nutrients. Fertilizers will display a series of three numbers separated by dashes. The main macronutrients for plants are Nitrogen, Phosphorus, and Potassium. For example, a 16-4-8 fertilizer has 16% Nitrogen, 4% Phosphorus, and 8% Potassium.
Nitrogen supports lush, vertical, and lateral leaf growth, and a Nitrogen-deficient grass will have a pale yellow shade. Applying Nitrogen to deficient grass will result in a greener lawn as long as there are no other issues present.
Phosphorus is essential for a strong root system and seed germination, and while applying Phosphorus may not present a large visual difference, it still plays a crucial role in plant development.
Similarly, Potassium may not present any visual difference after application, but it is essential for plants and grass, playing a role in photosynthesis and carbohydrate production. A Potassium-deficient lawn may also be less resilient to abiotic stressors, like extreme temperature and drought.
Micronutrients, such as Iron, Manganese, Magnesium, and more, are also essential but in smaller quantities. Iron is crucial for chlorophyll production, giving plants that deep green hue, and Manganese is important for absorbing Nitrogen. Fall is a great time to apply micro nutrient fertilizers to cool-season lawns to get that last green-up before winter dormancy.
When to Apply Fall Fertilizer
If you have cool-season grass, this is the best time to fertilize your grass, as this is the prime time to enjoy greening and growth from your lawn. You’ll want to apply lawn fertilizer, supplying Nitrogen and Potassium fertilizer from September up until before the first frost sets in.
If you have warm-season grass, you’re going to want to do lighter applications of Nitrogen fertilizer in September, with a higher Potash fertilizer application in October.
When it’s Too Late to Apply Fall Fertilizer
Depending on where you live, you’ll want to hold off on fertilizing at a certain point. Look out for your first frost date in your state or climate zone. For zone 1, the first frost can come as early as late August. Zones 2-4 can see frost in September or October. Mid-latitude regions (Zones 5–7) have moderate growing seasons—last frost mid to late April, first frost mid- to late October.
Southern and coastal regions (Zones 8–11) have extended or year-round growing seasons—frosts are rare or nonexistent. You may or may not want to fertilize in these areas, as the weather may still be too cold for your grass type, especially if you have a warm-season lawn.
Frost Dates for USDA Climate Zones & Last Fertilizer Timing
Fall Fertilizer and Overseeding
Before overseeding, you’ll want to remove any debris like sticks or leaves from your yard, and mow the lawn low. Mowing low allows more sun-to-soil contact for seedlings. Dethatch the lawn if needed to ensure that the yard is clear of debris that could block out any sun.
The day before laying seedlings, apply a Phosphorus-rich fertilizer. New seeds require constant moisture for the first 10-14 days. Water the seedlings with frequent, shallow waterings, just to keep the soil moist until germination. Once the seed has germinated, increase the time and reduce frequency for deeper watering. It is recommended to apply a Humic Acid soil amendment at this time to help grass uptake the nutrients needed to grow into mature grass.
Once the grass grows high enough to mow, you’ll want to apply a Nitrogen fertilizer. Our 16-4-8 fertilizer, Lawn Energizer, or 15-0-15 lawn fertilizer are great choices.
We have a special lawn fertilizer bundle designed for seeding a new lawn that contains all of the nutrients your new grass needs for starting a new lawn or overseeding.
Sources:
https://archive.lib.msu.edu/tic/mitgc/article/197297.pdf
https://pmc.ncbi.nlm.nih.gov/articles/PMC7996290/
