Fertilizer: What is in the Bag?

What do the letters and numbers mean on a fertilizer bag? Why is it important? These and many more questions are asked of us all the time. Let KCB explain it:

Fertilizer: with an NPK of 5-3-4

What do the letters mean?

1st letter = N for Nitrogen

2nd letter = P for Phosphorus

3rd letter = K for Potassium

What do the numbers mean?

The % by weight of the element in the mixture. A 10 pound bag of fertilizer labeled 5-10-5, it would contain 5% nitrogen, 10% phosphorus and 5% potassium. The remaining 80% could be comprised of other nutrients and filler.

What do these elements do?

Nitrogen: Aids in the above-ground leafy green growth. Enhances foliage.

Phosphorus: Supports root development, fruit & flowering. Also helps in the transfer of energy from one part of the plant to another. Fertilizers that promote bigger and more blooms will have a higher % than the other ingredients.

Potassium: Helps a plant fight disease and regulates the synthesis of proteins & starches

Extra Tip: Magnesium works especially well with potassium and should also be included in the fertilizer mix. It helps to maintain balance between the green foliage and the flower.

What else is in there?

Other nutrients like calcium, magnesium, iron, and micronutrients

Types of fertilizers

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

Granular – This is the most common bagged fertilizer product. It is best applied with a spreader and is long lasting. This is the version you’ll find in time release and can last in the soil up 6-9 months.

Water Soluble – This type of fertilizer is designed to dissolve in water and is more readily absorbable to your flowers and plants. This version only last in the soil 1-2 weeks however and need to be re-applied often to be as effective as granular fertilizers.

Natural Organic – This consists mostly of manures and bone meal. Yes they are natural, but they are lower in nutrient levels than synthetic versions mentioned Organic fertilizers made from natural ingredients often have lower concentrations of the three major nutrients, so you will need to use larger amounts. However, they do contain many other nutrients that feed both the plant and the soil. If you are using a synthetic fertilizer, you should supplement with some type of organic matter such as compost or manure, to maintain soil health.

KCB for Skillin's Greenhouses
March 30, 2010