When to Fertilize Your Lawn

This determines your entire fertilizer calendar. Cool-season grasses (Kentucky bluegrass, tall fescue, fine fescue, perennial ryegrass) feed heaviest in fall. Warm-season grasses (bermuda, zoysia, St. Augustine, centipede, bahia) feed heaviest in summer. Getting this wrong is the most common fertilizer mistake in the transition zone.

Cool-season: apply 0.5 lb nitrogen per 1,000 sq ft in late April after the second mowing. Do NOT apply heavy nitrogen in spring because it pushes top growth at the expense of root development. Warm-season: wait until the grass is fully green and actively growing (typically May) before the first application.

Warm-season grasses are growing fastest. Apply 0.5 to 1 lb nitrogen per 1,000 sq ft monthly from May through August. Cool-season grasses are under heat stress. Avoid nitrogen in July and August. An iron supplement (Milorganite, ferrous sulfate) provides color without the burn risk of nitrogen during hot weather.

Cool-season: apply 1 lb nitrogen at overseeding (September) and 1 to 1.5 lb as a winterizer in late October to November. The winterizer is the single most impactful application of the year. It feeds root energy storage and drives early spring green-up. Warm-season: last nitrogen by mid-September to allow hardening before dormancy.

No fertilizer for any grass type during winter dormancy. Cool-season grass isn't growing upward (the winterizer fed the roots). Warm-season grass is completely dormant. Fertilizer applied to frozen or dormant ground washes away with snow melt and contributes to nutrient runoff.