The United States Department of Agriculture (USDA) mandates that products sold as soil nutrients must have their minimum essential plant nutrients displayed prominently on the container (by percentage of weight). The order is: Nitrogen (N), Phosphorus (P) and Potassium (K). If a fourth number is present, it represents Sulphur, which is beneficial to acid-loving plants like Azaleas, Rhododendron, and Hydrangea.Fertilizer numbers
A ratio for "average" plants is 3-1-2, which is the same ratio as 6-2-4, or 12-4-8.
These ratios (by weight) mean that 100 pounds of 3-1-2 contains (at least):
3 pounds of Nitrogen, 1 pound of Phosphorus, and 2 pounds of Potassium.6 pounds of Nitrogen, 2 pound of Phosphorus, and 4 pounds of Potassium
are contained in 100 pounds of 6-2-4 (at least). The other 88 pounds is "filler".
If you could find 50-17-33, the ratio would be virtually the same.
But there would be no filler.It takes only 50 pounds of 6-2-4 to get the same benefit as 100 pounds of 3-1-2.
The higher concentrations may cost more, but may be cheaper in the long run, since less is used to obtain the same benefit. So if 40 pounds of 3-1-2 costs $5.00, then anything less than $10.00 for 40 pounds of 6-2-4 is the bargain.
