Kentucky Bluegrass is a popular cool-season grass known for its dense, deep green turf. Achieving this high-quality appearance requires a deliberate and well-timed maintenance strategy. Proper fertilization timing is particularly important to support its unique growth cycle and rhizomatous spreading habit, which allows the lawn to self-repair and thicken. Understanding when and how to feed Kentucky Bluegrass is essential for maintaining its health and density.
Understanding Kentucky Bluegrass Nutritional Needs
Kentucky Bluegrass is a cool-season turf, meaning its most active growth occurs in the spring and fall. It thrives when soil temperatures are between 50°F and 65°F, leading to two peak growth windows. During hot summer months, the grass slows its growth and may enter a semi-dormant state to conserve energy.
The grass relies heavily on Nitrogen (N) to fuel shoot growth and its horizontal spread via underground stems called rhizomes. While Nitrogen promotes a lush, green canopy, excessive spring feeding can inhibit root development by focusing energy on top growth. Therefore, the majority of nutrients should be delivered in the autumn when the grass naturally focuses on root and rhizome establishment.
The Annual Fertilization Calendar
The most effective approach for Kentucky Bluegrass involves a multi-step annual plan, typically broken into four critical applications that align with its cool-season nature.
Early Spring Application
The first application is a light feeding that occurs in mid-March to early April, as the grass begins to green up but before the soil temperature consistently reaches 55°F. This initial dose aids in green-up and recovery from winter. The application must be modest to avoid diverting energy away from deep root growth.
Late Spring Application
The second feeding is a moderate application scheduled for late spring, usually around May, after the initial rapid growth has subsided. This provides a steady nutrient supply to prepare the turf for the stresses of summer heat and potential drought. Using a slow-release nitrogen source during this period is beneficial for sustained feeding and minimizing the risk of burn.
Early Fall Application
This application, in early to mid-September, is considered the most important feeding of the year. It coincides with the grass’s return to its peak growing season, allowing the turf to recover from summer stress and rapidly repair damage. This nutrient boost is crucial for building a strong root system and maximizing the development of rhizomes, which increases turf density.
Late Fall or Dormant Feed
The final application occurs in late October or November, just before the ground freezes and growth stops. Often called a “winterizer,” this feed should be timed near the last mowing of the season. The grass absorbs these nutrients and stores them as carbohydrates in the rhizomes and roots, providing the energy reserves needed for early spring green-up the following year.
Selecting the Right Fertilizer
Fertilizers are labeled with an N-P-K ratio, representing the percentage of Nitrogen (N), Phosphorus (P), and Potassium (K) by weight. Nitrogen is the primary nutrient for Kentucky Bluegrass, driving lush color and dense growth. Annual application rates typically range from three to five pounds of actual nitrogen per 1,000 square feet. Phosphorus and Potassium should only be applied based on the results of a soil test.
The form of Nitrogen is a significant consideration, particularly to avoid excessive shoot growth in the spring. Quick-release nitrogen provides immediate greening but can weaken roots if applied too heavily. Slow-release nitrogen is preferred for spring and summer applications because it offers sustained feeding and reduces the risk of fertilizer burn. Conversely, the late fall dormant feed often benefits from a quick-release or soluble nitrogen source for rapid absorption before the grass enters full dormancy.
Best Practices for Application and Follow-Up Care
Before starting any fertilization regimen, perform a soil test to determine existing nutrient levels and pH. This analysis provides specific recommendations for Phosphorus and Potassium, ensuring optimal health. Adjusting the soil pH to the optimal range of 6.0 to 7.0 is also important for nutrient uptake.
Application Techniques
When applying granular fertilizer, properly calibrating the spreader is essential to ensure even distribution and prevent striping or burning the lawn. Apply the fertilizer to dry grass blades so the granules fall directly onto the soil surface. Immediately after application, the lawn must be thoroughly watered to dissolve the fertilizer and move the nutrients into the root zone.
Supporting Maintenance
General maintenance practices support the effectiveness of fertilizer applications. Mowing Kentucky Bluegrass at a slightly taller height, typically between 2.5 and 3.5 inches, encourages deeper root growth. This allows the plant to better withstand environmental stresses. Leaving the grass clippings on the lawn acts as a natural slow-release fertilizer, returning nitrogen and organic matter back to the soil.