Choosing the Right Starter Fertilizer for a New Lawn: N-P-K Explained

Confused by fertilizer numbers? Here’s a plain-English breakdown to protect tender grass seedlings.

What the Numbers Mean

Every fertilizer shows three percentages: N-P-K (Nitrogen–Phosphorus–Potassium).

• Nitrogen (N) – drives green leaf growth.
• Phosphorus (P) – fuels root development, flowering, fruiting.
• Potassium (K) – strengthens cell walls, drought and disease resistance.

Why Lawns Need High Nitrogen

Grass produces no flowers or fruit; its biomass is mostly leaf tissue. Mowing constantly removes nitrogen, so lawn fertilizers are N-heavy (e.g., 29-3-4, 28-0-0, urea 46-0-0).

Starter vs. Maintenance Fertilizer

• At seeding / early spring: A balanced starter (5-10-10, 10-10-10, or 20-27-5) ensures adequate P and K for root establishment.
• Once grass is actively growing and mowed: Switch to high-N fertilizer (28-0-0, 33-3-3, or urea 46-0-0).

How Much to Apply (Per 1,000 sq ft)

Divide 100 by the first number (N%) on the bag.

• 46-0-0 urea → 100 ÷ 46 ≈ 2 lbs
• 20-27-5 → 100 ÷ 20 = 5 lbs
• 5-10-10 → 100 ÷ 5 = 20 lbs

Higher-analysis products cost more per bag but cover far more area per pound—often cheaper overall. Calculate cost per 1,000 sq ft before buying.

Protecting Seedlings

Follow the rate above; never exceed it. Water after application. A starter fertilizer at seeding, then high-N once the lawn is established, gives the best results without burning tender sprouts.