Fertilizing a lawn in December involves a specific practice known as “winterizing,” which aims to prepare the turf for cold weather and dormancy. Whether this practice is appropriate depends almost entirely on the type of grass on your property and your specific regional climate. Applying nutrients at the wrong time or in the wrong region can be ineffective and harmful to the lawn, often leading to wasted product and potential environmental runoff.
Grass Type and Climate Considerations
The decision to fertilize in December is tied directly to the biology of your turfgrass, which is categorized into two main groups. Cool-season grasses, such as Kentucky Bluegrass, Fescue, and Perennial Ryegrass, are adapted to thrive in cooler temperatures. These grasses maintain root activity well into the late fall, even after the visible top growth has slowed down or stopped entirely.
Warm-season grasses (Bermuda, Zoysia, St. Augustine) enter dormancy once soil temperatures drop below 55°F. Once dormant, they cannot effectively absorb nutrients through their roots. Applying nitrogen to dormant warm-season grasses in December is discouraged, as the nutrients are wasted and can contribute to water pollution.
For cool-season varieties, the late-season application window often extends into December, particularly in regions with a moderate start to winter. The primary goal is to apply the fertilizer just before the ground freezes solid, allowing the active root system to take up the nutrients. This timing ensures the grass is still physiologically capable of benefiting from the feeding before the harshest winter weather arrives.
The Purpose of Late-Season Feeding
The goal of this final, late-season feeding is not to encourage the grass blades to grow taller, which would make the plant more susceptible to cold damage. Instead, the process is focused on strengthening the plant’s underground structures. The nutrients absorbed in late fall are primarily directed toward fortifying the root system, which continues to develop even as the leaf tissue remains dormant.
This practice facilitates the storage of carbohydrates within the crowns and rhizomes of the turf. These stored sugars are utilized throughout the winter for survival, increasing the plant’s cold hardiness. Carbohydrate reserves help the grass better withstand freezing temperatures, desiccation, and disease.
The stored energy provides a benefit in the following spring, promoting an earlier and more vigorous green-up. A ready supply of nutrients allows the grass to begin growth without needing an immediate spring nitrogen application. This late-season strategy supports a deeper, denser root mass, improving the lawn’s overall health and drought tolerance.
Choosing the Right Winterizing Product
The chemical composition of a December fertilizer must differ from summer or spring products, focusing specifically on the Nitrogen, Phosphorus, and Potassium (NPK) ratio. Potassium (K), the third number, is important for winterizing, aiding in cellular water retention and improving resistance to cold and disease stress. Look for products with a higher proportion of potassium relative to the other nutrients.
Nitrogen (N), the first number, should be applied conservatively to avoid stimulating excessive shoot growth that could be damaged by frost. The ideal ratio features a lower amount of nitrogen, such as a 2:1 ratio of Nitrogen to Potassium, or formulas like 21-0-20. The nitrogen component should be primarily water-soluble and quick-release, allowing the grass to absorb it rapidly before the ground freezes.
Phosphorus (P), the middle number, is often zero or very low unless a soil test indicates a deficiency. Many soils already have sufficient phosphorus, and its application is regulated in many areas due to environmental concerns over water runoff. Selecting a fertilizer with a zero in the middle slot is a safer approach for late-season feeding.
Application Guidelines and Safety
The fertilizer must be spread after the last mowing of the season but while the grass is still green and the soil is unfrozen. A soil temperature consistently below 50°F indicates that the grass has stopped active top growth. If the ground is already frozen, the roots cannot take up the nutrients, rendering the application useless.
It is important to apply fertilizer to a dry lawn to prevent the granules from sticking to wet blades, which can cause chemical burn. After spreading, the product must be “watered in” lightly to dissolve the granules and move the nutrients into the root zone where they can be absorbed. If heavy snow or rain is not immediately expected, a brief irrigation cycle is necessary.
Safety Guidelines
Safety guidelines must be followed to prevent nutrient burn and environmental contamination:
- Use a calibrated spreader to ensure even distribution.
- Avoid overlapping passes, which can result in nutrient burn.
- Use slightly less than the amount specified on the product label to prevent over-application and potential runoff.
- Never apply fertilizer directly onto frozen ground, as this significantly increases the risk of nutrient loss.