3/30/18 – Matt Rohman
The three numbers indicate the percentage by weight of the three main nutrients that grass needs: nitrogen, phosphorus, and potassium. The bag in the example picture indicates that the bag’s weight is 24% nitrogen, 0% phosphorous, and 12% potassium. This fertilizer would be called a “24-0-12” pronounced: “twenty-four, zero, twelve”
Since the example bag (and most all fertilizer bags) is 50 lbs, the simple trick to determine actual amount of each nutrient is to cut the number in half. In the example bag, there is 12 lbs of nitrogen, 0 lbs of phosphorous, and 6 lbs of potassium. (24/2, 0/2, and 12/2).
Why do most bags of fertilizer have 0% phosphorous?
- It is illegal to apply phosphorus to Minnesota lawns that don’t need it. Phosphorus is harmful to our waterways, causing excess algae and vegetation growth that sucks the oxygen out of the water and can kill aquatic life. Phosphorus should only be applied if a soil test warrants it or to aid in seed growth. Our metro soils generally have adequate phosphorus naturally. We’ve never received a soil analysis showing low phosphorus.
Check back for our next blog post about how to use these numbers to determine how much fertilizer to buy and apply to your lawn!
These “if I didn’t work at” posts are intended to show the DIYer how to get professional results on their lawn. Stay tuned for more.