This document provides information about interpreting fertilizer labels. It explains that most commercial fertilizers list three numbers on the label (N-P-K) which indicate the percentage by weight of nitrogen, phosphorus, and potassium, the three major plant nutrients. It gives an example of a 10 lb bag labeled 5-10-5, which would contain 0.5 lb nitrogen, 1 lb phosphorus, and 0.5 lb potassium. The document defines complete and incomplete fertilizers and explains what information is required on labels by law. It emphasizes that the first number refers to the nitrogen percentage and encourages foliage growth, the second to phosphorus for rooting and flowering, and the third to potassium for plant health.

1. Fertilizer Labels
Objective: Students will identify how
to interpret fertilizer labels.

2. What is fertilizer?
 A material applied to supply essential elements

3. Major Ingredients
1. Most commercial fertilizers have 3 numbers
on the front label, separated by dashes.
 For example: 5-10-5.
2. This is the fertilizer analysis or percentage
by weight of the 3 major nutrients plants
need:
 nitrogen, phosphorus and potassium, in that
order.
3. These are abbreviated as N-P-K.

4. Get out your Calculator and Analyze
1. If you purchased a 10 pound bag of fertilizer labeled 5-10-5,
it would contain…
 5% nitrogen
 10% phosphorus
 5% potassium.
 The remaining 80% could be comprised of other nutrients and
filler.
2. How many pounds of NP and K does it contain?
 .5 lb. nitrogen
 1 lb. phosphorus
 .5 lb. potassium
 The remaining 8 lbs could be comprised of other nutrients and
filler.

5. 1st Number = Nitrogen
1. The first number gives the concentration of
nitrogen in the product.
2. Nitrogen encourages foliage growth, among
other benefits.
3. A 5-10-5 fertilizer would contain 5% nitrogen
by weight.
4. For every pound of fertilizer applied there is
really only .05 pounds of nitrogen.
 (The 10 pound bag mentioned would contain .5 lb.
nitrogen)

6. 2nd Number = Phosphorous
1. The middle number refers to the concentration
of phosphorous.
2. Phosphorous contributes to many fundamental
plant processes such as rooting and setting
flower buds.
3. A 5-10-5 fertilizer would contain 10%
phosphorous by weight or .1 pounds of
phosphorous.
 (The 10 pound bag mentioned above would
contain 1 lb. of phosphorus.)

7. 3rd Number = Potassium
1. The final number states the concentration of
potassium.
2. Potassium contributes to the overall health and
vigor of plants.
3. Again, a 5-10-5 fertilizer would contain 5%
potassium by weight or .05 pounds of
potassium.
 (The 10 pound bag mentioned above would
contain .5 lb. potassium.)

8. Complete Fertilizers
1. Fertilizers that contain all three major
nutrients are considered complete fertilizers.
2. There are specialized fertilizers which are
called incomplete because they lack one or
more major nutrients such as a fertilizer
labeled 0-20-20.

9. Fertilizer Label
1. Some information is required by law
to be on the fertilizer bags:
1. Net Weight
2. Brand and grade of fertilizer
3. Guaranteed analysis of each
nutrient in fertilizer
4. Name and address of
manufacturer

10. Other Valuable Information
 Some manufacturers add the following
on the bag as well:
 % of water insoluble nitrogen
 Potential acidity
 Salt index
 Source of carrier
 % of minor elements
 Calculation rates
 How to calibrate spreaders

11. Reading a Fertilizer Label
 N- 24 %
 P- 5 %
 K- 11 %
 Remaining 60% is other
nutrients and filler.

12. Analyze This!
What do you know from the bag?
N: 24 %
P: 6 %
K: 12 %
Use: Lawn Fertilizer

13. Check for Understanding
1. Jack and Jill went up the hill and noticed the
grass was very yellow. Which fertilizer
would be best for them to use, 12-12-12, 28-
14-14 or 4-16-4?
28-14-14
 Why?
 Nitrogen is used to help promote lush green
foliage growth, the 28-14-14 fertilizer is the
highest in nitrogen.

14. Practice Reading the Label
 In the boxes on your worksheet please provide
the following information for each fertilizer
placed on the tables around the class…
 Net Weight
 Brand and grade of fertilizer
 Name of manufacturer
 NPK percentage
 One Secondary nutrient and %
 One Micronutrient and %

15. Name of manufacturer, Brand and grade of
fertilizer, Use, Net Weight, NPK percentage, One
Secondary or Micronutrient and %