Why you should fertilize your lawn
Just like humans require a balanced diet for healthy growth, grass requires certain essential nutrients for normal, healthy growth. Keeping your lawn supplied with sufficient nutrients will help it grow stronger, look greener, and be more resistant to disease and drought.
The three key nutrients for healthy grass growth are:
- Nitrogen (N) — Required in the highest amounts. Deficiency causes yellowing of leaves.
- Phosphorus (P) — Important for photosynthesis and root development. Deficiency causes slow growth and purplish leaves.
- Potassium (K) — Supports respiration and osmotic regulation. Deficiency causes browning leaf tips.
What does N-P-K stand for?
The N-P-K numbers on a fertilizer label tell you what percent of the bag's weight is composed of Nitrogen (N), Phosphate (P₂O₅), and Potassium (K₂O).
For example, a bag labeled 25-5-10 contains 25% nitrogen, 5% phosphate, and 10% potash by weight.
How to choose a fertilizer
Look for a fertilizer with slow-release nitrogen (sometimes called "controlled-release" or "slowly available"). Benefits include:
- Nitrogen becomes available slowly over time, keeping the lawn fed longer.
- Less likely to overfertilize and burn your grass.
- Reduces water pollution from nitrate leaching.
How to calculate fertilizer application rates
- Calculate fertilizer rate:Fertilizer rate = Desired N rate / (%N on label / 100)
- Calculate total fertilizer needed:Fertilizer weight = Rate × Area
- Calculate bags needed:Bags = Total fertilizer / Bag weight
Example: For a 28-0-6 fertilizer at 1 lb N/1000 sq ft on a 5000 sq ft lawn: Rate = 1/(28/100) = 3.57 lbs/1000 sq ft. Total = 3.57 × 5 = 17.9 lbs.
Why should I get a soil test?
A soil test provides an accurate picture of existing nutrient levels. Benefits include matching nutrients to your specific grass species, saving money by not over-applying, avoiding grass burn, and monitoring soil pH (most lawns do well between 6.5–7.0).
When is the best time to fertilize?
For seasonal climates with winters below 55°F (13°C), the best time to fertilize is in the fall. Fall fertilization builds strong roots before winter, so the lawn rebounds quickly in spring. If you only fertilize once a year, fall is the best choice.
Environmental considerations
Excess fertilizer can harm aquatic life. It leaches into waterways, feeding algal blooms that deplete oxygen and create "dead zones." To prevent this:
- Use only what your soil needs — test first.
- Sweep up fertilizer from sidewalks and driveways.
- Spread applications across multiple smaller doses throughout the year.
- Consider organic fertilizers, which are less prone to leaching.