Lawn Fertilizer Calculator
Applying the correct amount of fertilizer prevents waste, environmental runoff, and lawn damage from over-application. This calculator determines how much product to apply based on your lawn size, grass type, and the fertilizer's nutrient ratio (N-P-K).
Fertilizer Application
Never apply more than 1 lb of nitrogen per 1,000 sq ft in a single application. Excess fertilizer runs off into waterways and can burn turf. Always water in after applying granular fertilizer. Follow all local fertilizer ordinance restrictions.
Nitrogen Needs by Grass Type
| Grass Type | Annual N (lbs/1,000 sq ft) | Applications/Year | Season |
|---|---|---|---|
| Bermuda Grass | 3–5 | 4–6 | Warm (Apr–Sep) |
| St. Augustine | 2–4 | 3–4 | Warm (Mar–Oct) |
| Zoysia Grass | 2–3 | 2–4 | Warm (May–Aug) |
| Centipede Grass | 1–2 | 1–2 | Warm (Apr–Jul) |
| Tall Fescue | 2–4 | 2–4 | Cool (Sep–Nov, Mar–May) |
| Kentucky Bluegrass | 3–5 | 3–5 | Cool (Sep–Nov, Apr–May) |
| Perennial Ryegrass | 3–4 | 3–4 | Cool (Sep–Nov, Mar–May) |
| Bahia Grass | 2–3 | 2–3 | Warm (Apr–Sep) |
Understanding N-P-K
The three numbers on a fertilizer bag represent the percentage by weight of three key nutrients:
- N (Nitrogen) — drives leaf growth and green color
- P (Phosphorus) — supports root development and establishment
- K (Potassium) — improves drought tolerance, disease resistance, and cold hardiness
A 50-lb bag of 24-4-12 fertilizer contains 12 lbs of nitrogen (50 × 0.24), 2 lbs of phosphorus, and 6 lbs of potassium.
Frequently Asked Questions
When is the best time to fertilize?
For warm-season grasses (Bermuda, St. Augustine, Zoysia), fertilize when the grass is actively growing — typically April through September. For cool-season grasses (Fescue, Bluegrass, Ryegrass), the most important application is in fall (September–November), with a lighter feeding in spring.
Should I use slow-release or quick-release fertilizer?
Slow-release (controlled-release) fertilizers feed over 6–12 weeks and are less likely to burn turf or leach into groundwater. Quick-release provides faster green-up but requires more frequent, smaller applications. Most lawn fertilizers are a blend of both.
Can I fertilize a wet lawn?
Granular fertilizer can be applied to a damp lawn, but avoid applying during heavy rain (runoff risk) or to wet foliage with liquid fertilizer (burn risk). Water in granular fertilizer within 24 hours of application.