All fertilizers have three numbers on the label which indicate the fertilizer analysis, or “percentage by weight” of nitrogen, phosphorus, and potassium, in that order.

Therefore, a 50 pound bag of fertilizer labeled 20-10-5 would contain 20% nitrogen (10 pounds), 10% available phosphates (5 pounds) and 5% soluble potash (2.5 pounds). See the calculations below:

EXAMPLE: 50 pound bag of 20-10-5 fertilizer

20% nitrogen .20 x 50 lbs = 10 lbs

10% available phosphates .10 x 50 lbs = 5 lbs

5% water soluble potash .05 x 50 lbs = 2.5 lbs

This fertilizer would be considered a “complete” fertilizer, since all three nutrients are present.

An “incomplete” fertilizer might have a label like 0-0-60 or 46-0-0, since it would only have one of the three major nutrients present. Another example of an incomplete fertilizer would be 0-20-20, since one of the three nutrients (nitrogen) is missing.