To determine how much fertilizer to apply to your lawn, the key factor is the amount of nitrogen (N) recommended per 1,000 square feet, as nitrogen is the primary nutrient for lawn growth.
General Guidelines for Fertilizer Amount
- A common recommendation is to apply 1 pound of nitrogen per 1,000 square feet per application. For the entire growing season, about 3 to 6 pounds of nitrogen per 1,000 square feet is typical, divided into multiple applications (usually 4 times a year)
- For shaded lawns, use about half the nitrogen amount compared to lawns in full sun to avoid excessive shoot growth and disease susceptibility
How to Calculate the Amount of Fertilizer to Apply
- Check the nitrogen percentage on your fertilizer bag (the first number in the N-P-K ratio). For example, a 20-0-10 fertilizer contains 20% nitrogen.
- Calculate pounds of fertilizer needed per 1,000 sq ft by dividing the desired nitrogen rate by the decimal form of the nitrogen percentage:
Pounds of fertilizer per 1,000 sq ft=Desired pounds of NNitrogen % as decimal\text{Pounds of fertilizer per 1,000 sq ft}=\frac{\text{Desired pounds of N}}{\text{Nitrogen % as decimal}}Pounds of fertilizer per 1,000 sq ft=Nitrogen % as decimalDesired pounds of N
For example, if you want 1 pound of nitrogen per 1,000 sq ft and your fertilizer is 20% nitrogen:
10.20=5 pounds of fertilizer per 1,000 sq ft\frac{1}{0.20}=5\text{ pounds of fertilizer per 1,000 sq ft}0.201=5 pounds of fertilizer per 1,000 sq ft
- Multiply by your lawn size in thousands of square feet to get the total fertilizer amount. For example, a 7,000 sq ft lawn with 15% nitrogen fertilizer (15-0-10) and 1 lb N/1,000 sq ft:
- Pounds per 1,000 sq ft = 1/0.15=6.671/0.15=6.671/0.15=6.67 pounds
- Total fertilizer = 6.67×7=46.76.67\times 7=46.76.67×7=46.7 pounds
Summary
- Apply about 1 pound of nitrogen per 1,000 square feet per application.
- Adjust fertilizer amount based on nitrogen percentage on the bag.
- Divide total lawn area by 1,000 and multiply by the fertilizer amount per 1,000 sq ft.
- Split the total seasonal nitrogen into 3-4 applications.
- Use less nitrogen for shaded lawns (about half).
This method helps you avoid over-fertilizing, saving money and protecting the environment
