Fertilizer Numbers – What do the numbers on fertilizer label mean? Why are they important?
Here’s the deal. Fertilizing plants comes at a cost – in time, in money and results!
To get the most from your “plant food” dollar, keep clearly in mind why you are fertilizing.
Each fertilizer product has a definite purpose and the numbers on the label tell the purpose.
The one you should use depends upon:
- Your soil – Is the soil friable (easily crumbles) or hard packed?
- Is the soil acid or alkali?
- Are you growing the plant for its leaves, flowers, or roots?
- The results you expect.
Did you conduct a soil test to find out its soil pH? The test results tell you if any additional soil amendments are needed.
Do you want quick action from the plant food for a short quick green color or a slow-release fertilizer action over a longer time period?
These are the things to consider in selecting a fertilizer.
A wrong fertilizer choice is not only a waste of effort and money but can actually be worse than no fertilizer at all!
3 Numbers On Fertilizer
To ensure good plant growth, they require:
- Nitrogen (first number) – to stimulate the growth of foliage
- Phosphorus (second number) – to encourage the development of fruit and flowers
- Potash (third number) – to stimulate the growth of strong roots
- plus minute amounts of trace minerals
Nitrogen is the most quickly used up and, therefore, the one that must be replaced most often.
How To Read Fertilizer Labels
Every container or bag of fertilizer you purchase on the market will have a fertilizer label.
The label will have the N-P-K ratio of the fertilizer. These “fertilizer numbers” tell buyers how much of the plant nutrients each “bag of fertilizer” contains.
The NPK acronym stands for Nitrogen, Phosphorus and Potassium. These are often referred to as “macro-nutrients.”
The fertilizer label also provides other information on the make-up and use of this fertilizer blend.
- The nitrogen sources and how many pounds of nitrogen
- Is the blend a water-soluble liquid fertilizer or a slow-release granular fertilizer
What is the fertilizer blends primary use?
- For root development and strong, healthy root growth
- To encourage the growth of foliage
- To help in fruit production
The “Complete Fertilizer” – Different Plants Use Specific Fertilizers
A so-called “complete fertilizer” is one which contains all three of these N-P-K nutrients.
Since different types of plants require different amounts of each food – no one fertilizer is a “COMPLETE ALL-PURPOSE FERTILIZER” for all plants.
The fertilizer that makes the wisteria bloom may cause the caladium to wear itself out producing unwanted flowers instead of fancy leaves.
The correct fertilizer for the fragrant-leaved geranium plant whose flowers are unimportant is wrong for the zonal geranium from which you expect blossoms.
If you are growing fruit or flower plants – tomatoes, roses, strawberries, candytuft – use a fertilizer high in phosphoric acid.
For root crops such as potatoes, carrots, and beets, look for a high potash content.
Two Fertilizer Groups – Chemical and Organic Plant Food
Fertilizers are divided into two groups – chemical and organic fertilizers. Each group has advantages and disadvantages.
Chemical fertilizers sometimes called synthetic fertilizers are quick acting and cheap. In addition, they are made according to a definite formula.
When you buy one you know exactly the percentage of nitrogen, phosphoric acid, and potash in each 50-pound bag of fertilizer and whether or not it contains trace minerals.
Under the trade name on each fertilizer bag or bottle will be three numbers, for instance, 5-10-5.
The first number indicates the percentage of nitrogen, the second number of phosphoric acid, and the third number of potash.
Thus, you can easily select a fertilizer that is high in whatever your plant particularly needs.
For example, you may select fertilizer ratios with plant food numbers of:
- A 5-8-7 formula for growing potatoes
- Select the formula 8-4-4 for celery
- For roses a 4-12-4 blend
- For tomatoes a 4-6-6 mix
A general all-purpose fertilizer mixture is 5-10-5. The base of a chemical fertilizer is usually sand.
Chemical fertilizer applications should be done strictly according to the directions on the fertilizer label.
An overdose of chemical fertilizers can burn a lawn or green leaves on a plant or even cause them to die.
A teacup holds about one-half a pound of fertilizer. Always water fertilizer in thoroughly, and never let it touch the foliage or stems.
Commercial fertilizers use up the humus in the soil. They are short lasting and often leave a residue in the soil that causes an acid or alkali reaction.
Therefore, you should not use the same chemical mixture on the soil year after year. You must also add large quantities of humus to replace that which is lost.
Organic fertilizer is slow acting, long lasting, and build up the soil in the garden over a long period of time.
Because of their slow action, they may be used more freely with less danger of overfertilizing.
For example, several organic lawn fertilizers include fish emulsion,
Organic fertilizers high in nitrogen are:
- Manure – besides the nitrogen and organic matter, manure contains soil improving bacteria
- Cottonseed meal (6-1-1)
- Blood Meal (13-0-0)
The best organic sources of phosphoric acid are:
- Bone Meal (0-10-0)
- Rock phosphates
Organic potash is found in:
- Ashes of hardwood trees
The value of the “food” in organic fertilizers varies making it difficult to label them as precisely as synthetic fertilizers.
Organic mixtures are packaged, but with the approximate nutrient percentage on the bag.
Any fertilizer can be overused, however. Every plant has a saturation point beyond which more fertilizer is bad.
Plants seem to be affected by too much fertilizer just as human beings are by too rich a diet.
Remember, too, that some plants such as Nasturtiums and certain herbs actually prefer a rather poor soil.
A good rule of thumb in choosing between a chemical and an organic fertilizer is this:
If you are primarily interested in the crop that year – annual flowers, tomatoes, etc. – use chemical.
If you are more interested in long-term growth as in the case of trees and shrubs, long-lasting bulbs, and perennials, then use organic.