Maryland lawns primarily consist of cool-season turf varieties. Because the state is in the transition zone, these grasses thrive during the spring and fall, but their active growth must eventually halt for the winter season. The precise moment this happens is not tied to a fixed date, but rather to a shift in environmental conditions that triggers cold-weather dormancy. Understanding this timing is necessary for homeowners to properly prepare their turf for the winter.
The Role of Temperature in Grass Dormancy
The cessation of grass growth is primarily dictated by the temperature of the soil, not the air temperature. Cool-season grasses experience their most robust shoot and leaf growth when air temperatures range between 60°F and 75°F. However, the root system functions best when soil temperatures are slightly cooler, ideally between 50°F and 65°F.
A significant slowdown in active vertical growth begins once the soil temperature consistently drops below the 50°F mark. This cooling signals the turf to conserve energy and begin storing carbohydrates in its crowns and roots for survival through the winter. While the visible leaf blades stop growing, the roots can continue to develop slowly until the soil temperature drops further, typically reaching around 33°F. This biological mechanism ensures the grass enters a protective, semi-dormant state before the ground freezes.
Identifying the End of the Growing Season in Maryland
For Maryland properties, the end of the active growing season typically falls within a window from late October to mid-December. This broad range exists because the shift in soil temperature occurs at different times across the state’s varied geography. Properties located in the cooler, higher elevations of Western Maryland will experience the end of growth earlier, often closer to late October or early November.
Conversely, lawns in the warmer regions of Southern Maryland and the Eastern Shore may continue to require mowing into November or even early December. A general benchmark for many central Maryland areas is that the final mowing often occurs around the Thanksgiving holiday. The yearly variability in weather patterns means that the lawn will continue to grow until the soil temperature threshold is met, regardless of the calendar month. Therefore, homeowners should pay attention to signs of growth slowing down, rather than relying on a predetermined date, to confirm the season’s end.
Preparing the Lawn for Dormancy
As the grass growth slows significantly, there are two actions that help prepare the turf for winter dormancy.
Final Mowing Height
The final cut of the season should be mowed at a height slightly lower than its regular maintenance level, generally aiming for 2 to 2.5 inches. This shorter height limits the amount of leaf tissue available to harbor moisture. It also prevents the development of fungal diseases like snow mold under a prolonged layer of snow.
Winterizing Fertilizer Application
The second necessary step is the application of a specialized winterizing fertilizer, timed for when soil temperatures are consistently in the 40s. This product is formulated to be high in both nitrogen and potassium, which are important for root health during the cold months. The late-season nitrogen is not used for top growth but is instead stored in the root crowns to promote an earlier and more vigorous green-up in the spring. The high potassium content supports the turf’s overall cellular strength, helping the grass better withstand the environmental stresses of freezing temperatures.