When and how to fertilize in spring?

When seeding bare patches or overseeding in spring, use a starter fertilizer with higher phosphorus (e.g., 10-18-10 or similar) applied at the time of seeding.

Before buying any fertilizer, send a soil sample to your county extension lab. The test costs $15-30 and tells you exactly what your soil needs — and what it already has enough of.

Do not fertilize bermuda, zoysia, St. Augustine, or centipede grass until it has fully greened up and is actively growing. This means waiting until 2-3 weeks after the last frost, when nighttime temperatures are consistently above 60-65°F.

Limit spring nitrogen to no more than 0.5 lb of actual nitrogen per 1,000 sq ft. Save the heavier applications (0.75-1 lb N per 1,000 sq ft) for fall, which is the most important fertilization window for cool-season grasses.

Use a soil thermometer to guide fertilizer timing rather than calendar dates. For cool-season grasses, wait until soil temperature at 4-inch depth consistently reaches 55°F. For warm-season grasses, wait until soil hits 65-70°F.

Spread a quarter-inch layer of screened compost over the lawn, ideally after core aeration. One cubic yard covers approximately 1,000 sq ft at this depth.

Spread corn gluten meal (9-0-0) at 20 lbs per 1,000 sq ft in mid-spring. It provides slow-release nitrogen and has a mild pre-emergent effect on crabgrass and other annual weeds.

Apply Milorganite (6-4-0) at 16 lbs per 1,000 sq ft in late spring. It releases nitrogen slowly over 8-10 weeks and includes 2.5% iron for natural dark green color without surge growth.

Choose a slow-release granular fertilizer (look for "slow-release" or "controlled-release" on the label) and apply at the bag rate in late spring, typically late May for cool-season lawns.

Do not rush to fertilize as soon as the lawn greens up. Wait until you have mowed the lawn at least twice, which ensures the grass is actively growing and can actually use the nutrients.