Grass dormancy is the natural resting phase a lawn enters to survive environmental stress. When the grass blades turn brown or tan, the plant has temporarily shut down its growth processes. Fertilizing a lawn in this state is generally not recommended, though the timing of application relative to the onset of dormancy is a significant factor. Understanding the difference between a truly dormant lawn and one merely preparing for a seasonal transition is important for effective nutrient application.
Defining the Types of Grass Dormancy
Grass enters a dormant state for one of two primary reasons, both resulting in the characteristic browning of the blades. Seasonal dormancy is a predictable, temperature-driven cycle. Warm-season grasses (like Bermuda or Zoysia) enter this state when temperatures drop consistently below approximately 50°F and remain brown throughout the winter. Cool-season grasses (such as Fescue or Kentucky Bluegrass) also experience a natural slowdown when soil temperatures fall below this threshold.
The second type is stress dormancy, usually triggered by a lack of moisture or extreme heat during summer drought conditions. The grass turns brown as a survival mechanism to conserve water. While the blades appear dead, the crown and roots remain alive, prepared to resume growth when conditions improve. This type of dormancy can be reversed quickly once adequate water is supplied.
In either state, the grass conserves energy and water by reducing its overall growth and nutrient uptake. A truly dormant lawn, particularly one in deep winter, has minimal physiological activity occurring in the roots.
Why Fertilizing Fully Dormant Grass is Harmful
Applying fertilizer to a fully dormant lawn is largely ineffective and potentially damaging because the grass is not actively growing or absorbing water. Since the roots are not actively translocating water or nutrients, the fertilizer cannot be taken up by the plant. This results in wasted product, as the nutrients simply sit on the surface or leach into the environment.
A more serious risk comes from the unabsorbed salt content in many synthetic fertilizers. When the grass is completely inactive, these salts remain concentrated on the soil surface and around the plant’s crown. This concentration significantly increases the risk of chemical burn, which can damage the grass when it eventually attempts to revive.
Applying a general fertilizer can also inadvertently stimulate the growth of metabolically active weeds while the turfgrass is in survival mode. This nutrient boost allows weeds to gain a competitive advantage over the weakened turf, making later weed control more difficult. Waiting until the grass shows signs of recovery or active growth is preferable for most fertilizer applications.
The Benefits of Late-Season Nutrient Application
The exception to avoiding fertilizer is the strategic late-season or winterizing feeding. This application occurs during the transition period just before deep winter, not when the grass is fully dormant. Optimal timing is when air temperatures are consistently cool enough to stop upward blade growth, but the soil has not yet frozen. This window allows the roots to remain active even though the shoots are not growing.
This late-season application is intended to build underground reserves for the coming spring, not to promote greening of the blades. The nutrients enhance root growth and increase the storage of non-structural carbohydrates in the plant’s crown and rhizomes. These stored carbohydrates are utilized for earlier spring green-up and improved tolerance to summer stress the following year.
The type of fertilizer matters significantly for this purpose. Experts recommend a slow-release formula that is moderate in nitrogen, low in phosphorus, and high in potassium. Potassium is particularly beneficial as it strengthens the plant’s cell walls, improving cold hardiness and overall resilience. A common NPK ratio, such as 12-0-24, focuses energy on root development and winter survival rather than excessive shoot growth.