Best Time to Fertilize Your Lawn in St. Petersburg, FL

Fertilizing a St. Pete lawn is not as simple as "spring and fall." Pinellas County has specific fertilizer ordinances, and Florida's climate means your timing windows are different from most of the country. Here is what you need to know.

The Pinellas County Nitrogen Blackout Period

You cannot apply nitrogen or phosphorus fertilizer from June 1 through September 30. This is Pinellas County's summer fertilizer blackout ordinance, adopted to reduce nutrient runoff into Tampa Bay during the rainy season. Heavy rainfall washes nitrogen directly into storm drains and then into the bay, causing algae blooms that harm marine ecosystems.

The Two Best Fertilization Windows

Window 1: April – May (Spring) — This is the optimal primary fertilization time. The lawn is actively growing, temperatures are warm, and there is enough time for uptake before the blackout period. Apply a slow-release nitrogen fertilizer in April once the lawn has been actively growing for a few weeks.

Window 2: October – November (Fall) — After the blackout ends September 30, you can apply again. This is a good time for a potassium-rich fertilizer to strengthen the lawn for winter. A second nitrogen application in October is appropriate if the lawn looks thin or pale after a hot summer.

What to Use — Pinellas County Rules

• Slow-release nitrogen only: At least 65% of the nitrogen must be slow-release. Fast-release nitrogen (like ammonium nitrate) is more prone to leaching and burning.
• Zero or minimal phosphorus: Most St. Pete soils have adequate phosphorus. Look for fertilizers labeled 15-0-15 or similar with zero or very low middle number.
• Keep granules off hard surfaces: Sweep any fertilizer that lands on driveways or sidewalks back onto the lawn. Granules on impervious surfaces go directly into storm drains.

What to Do During the Blackout

You can still apply iron supplements during the blackout period — iron is not nitrogen. If your lawn is looking pale during summer, a chelated iron spray (not nitrogen) is a legal and effective way to green it up. Potassium is also allowed during the blackout.

Do Not Fertilize Stressed Grass

Fertilizing a lawn that is drought-stressed, disease-ridden, or pest-damaged makes things worse. Fix the underlying problem first — water it if thirsty, treat pests if present — then fertilize healthy, actively growing grass.