Fertilizer calculator
Turn a soil-test recommendation, in pounds of a nutrient per 1,000 square feet, into pounds or ounces of the product on your bag for your own beds.
Use one line of your soil test report at a time: a recommendation in pounds of a nutrient per 1,000 square feet. Enter the percent of that nutrient from the bag you have: the first label number for nitrogen (N), the second for phosphate (P2O5), the third for potash (K2O).
Assumptions behind the numbers
- The recommendation must come from your soil test report or the product label. This calculator generates no recommendation.
- The three label numbers are percent by weight of N, P2O5 and K2O (Clemson HGIC 1228). Enter the number for the nutrient the recommendation names, in the same form (P2O5, not P).
- Pounds of product = pounds of nutrient / (percent / 100), the method worked in University of Maryland Extension's Fertilizing Vegetable Gardens and NMSU Guide H-120.
- 1 lb = 16 oz. Weigh small amounts on a kitchen scale kept for garden use; a cup of granules does not weigh the same across products.
The Okafor garden, as in Module 9: the lab report on their bed fill recommends 2 lb of nitrogen per 1,000 sq ft for the season in two equal parts, and no phosphorus or potassium. Each part is 1 lb N per 1,000 sq ft. Their bag reads 12-0-0. Pounds of product per 1,000 sq ft = 1 / 0.12 = 8.33 lb. For their 64 sq ft: 8.33 x 64 / 1,000 = 0.53 lb, about 8.5 oz per application, split between the two beds. The report and the bag are invented for the example; the lab report and the label you hold settle the real numbers.
The calculator turns a recommendation into a product amount. It does not decide whether your soil needs anything; only a soil test does (Module 3). Without one, follow the product label. Some places restrict phosphorus fertilizer on lawns and gardens; check local rules. Module 9 covers timing, side-dressing and runoff.