Fall fertilization is often considered the most important feeding of the year for turfgrass. This seasonal application shifts the plant’s focus from producing new leaf blades to building underground reserves. Providing nutrients in the autumn prepares the grass for the upcoming dormant season and the stresses of winter. This preparation determines how well the lawn survives the cold and how quickly it recovers with vibrant color in the spring.
The Purpose of Fertilizing in Autumn
Fertilizing in the autumn encourages a fundamental physiological shift in the grass plant, differing from spring or summer feeding. As air temperatures cool but the soil remains relatively warm, the plant directs its energy toward root growth rather than excessive top growth. This supports the development of a deeper, more robust root system, improving the plant’s ability to absorb water and nutrients.
The nutrients applied in the fall are converted into carbohydrates, a form of stored energy, and translocated to the plant’s crowns and roots. These stored carbohydrates sustain the plant through the winter months when active growth is limited. This reserve supports new growth and an early green-up after the spring thaw. Fall feeding also helps the turf recover from the stress of summer heat, drought, and heavy use, promoting increased density and health before dormancy.
Selecting the Right Nutrient Ratio
When selecting a fall fertilizer, understanding the three numbers on the label, known as the N-P-K ratio, is necessary. These numbers represent the percentage by weight of Nitrogen (N), Phosphate (P), and Potash (K). Fall formulations, often marketed as “winterizers,” emphasize Potassium (K), utilizing a moderate amount of Nitrogen and often little to no Phosphorus.
The increased concentration of Potassium (K) is beneficial because it does not promote rapid top growth but strengthens the plant’s internal structure. Potassium regulates water movement and strengthens cell walls, increasing the grass’s cold hardiness and resistance to winter diseases like snow mold. A common ratio for a winterizer is around 10-0-20 or a similar blend where Potassium content is high relative to the other nutrients.
Nitrogen (N) is necessary in the fall to support carbohydrate storage and continued root development. It is recommended to choose a formula containing slow-release Nitrogen sources, which provide a steady supply of nutrients over several weeks. This steady feeding minimizes the risk of a sudden growth surge that produces tender new leaf tissue susceptible to damage from an early hard frost. Phosphorus (P) is essential for root development; however, due to environmental concerns regarding water runoff, it should only be included if a soil test confirms a deficiency.
Proper Timing and Application Techniques
The effectiveness of fall fertilization depends on applying the product at the correct time. This is generally when the grass has begun to slow its upward growth but the roots are still actively growing. For cool-season grasses, this window opens about four to six weeks before the first expected hard frost, often between late September and late November. Applying the fertilizer too early risks stimulating excessive top growth, while applying it too late means the nutrients cannot be fully absorbed before the ground freezes.
Before application, mow the lawn to its normal height and clear any heavy leaf cover to ensure the granules reach the soil surface. The most reliable method for achieving even distribution is using a broadcast or rotary spreader. This prevents the streaking and burning that result from uneven application. Always calibrate the spreader according to the product label instructions to avoid over-application, which can harm the lawn and lead to nutrient runoff.
After the fertilizer has been spread, water the area lightly to dissolve the granules and wash the nutrients into the root zone. Watering prevents the fertilizer from sitting on the leaf blades, which can cause chemical burn, and allows the plant to begin absorbing the materials. Keep the product away from sidewalks and driveways, as runoff from these surfaces can carry excess nutrients into local waterways.