Summer 2004You find a bag of fertilizer with a label of 10-6-4. You know these numbers represent nitrogen, phosphorus and potassium, so you think there are 10 pounds of nitrogen in the bag, 6 pounds of phosphorus and 4 pounds of potash. Many gardeners and homeowners think this way because they’ve been trained to read fertilizer formulas the wrong way.
Yes, fertilizer labels are wrong, dead wrong. It’s not your fault. It’s confusing because fertilizer labels required by the government are misleading!
The formula for a bag of 10-6-4 means there are 10 pounds of nitrogen IN A 100-POUND BAG, not the one you’re looking at. If you buy a 50-pound bag of 10-6-4, then there are only half the amount of nutrients in your bag, namely 5 pounds of nitrogen, 3 pounds of phosphorus, and 2 pounds of potash. Fertilizer labels are misleading because the numbers are based on 100 pound bags.
Consider a 19-pound bag of Turf Trust lawn fertilizer, with a formula of 24-2-12. To know how much nitrogen, phosphorus and potassium is in each pound of Turf Trust, just move the decimal points to reflect the per-pound rate. For nitrogen, the per-pound rate is .24 pounds. The bag being 19 pounds, multiply .24 by 19 and you know there are 4.56 pounds of nitrogen in the bag of Turf Trust. The label says the bag covers 5,000 square feet. Dividing five into 4.56 means you are applying .91 pounds of slow-release nitrogen for each thousand square feet of lawn area. Slow-release nitrogen will release its nutrients to your lawn over a period of 10-plus weeks
Let’s explore another label, that of Milorganite (6-2-0) available in 40-pound bags at the nursery. The per-pound nitrogen rate is .06. We continue to recommend a late June application of Milorganite at 10 pounds per thousand square feet. Multiplying .06 by 10 means you are applying .6 (six-tenths of a pound) of organic nitrogen for every thousand square foot of lawn area, and .2 (two tenths of a pound) of phosphorus over the same area. Milorganite contains no potash. Since Milorganite is all-organic, the fertilizer will release to the lawn over a period of eight weeks as long as soil temperatures remain above 53 degrees.
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