Fertilizer Numbers

Fertilizer for garden plants can be a bit of a mystery at times. Personally I prefer organic fertilizer over synthetic plant fertilizer, but regardless what you use it is helpful to have a general understanding of their components.

When buying fertilizer you will see on the bag label it’s particular formula for fertilizer NPK.  N refers to Nitrogen, P refers to Phosphorous and K to Potassium. These three elements are the most important plant nutrients and are often referred to as primary macronutrients. They are necessary to the development and growth of all plants.

Sensible Gardening and Living
Sensible Gardening and Living

Numbers on Fertilizer Labels

Nitrogen Fertilizer:

Without adequate nitrogen plant growth is stunted and the plant may yellow from the bottom up.  Nitrogen is also essential for soil microorganisms whose job it is to change organic matter into nutrients that plants can absorb. Nitrogen maintains the green colour of plants and is required for strong stem and leaf growth. Giving nitrogen is like a quick fix for plants.

Phosphorous Fertilizer:

Phosphorous is necessary for photosynthesis. This is the process in which plants convert light energy into food. Phosphorous is also required for flower, fruit and seed development. Phosphorus is responsible for the general growth and health of plants, most importantly the root structure.

Seed Heads of Pineapple Plant / Sensible Gardening .jpg

Potassium Fertilizer:

The role of potassium is to help plants regulate the amount of water in their cells. Potassium plays a large role in the general health of plants as well as their ability to resist disease and pests. If a deficiency exists, it will first be noticed in the older growth tissues.

Different fertilizers will have different ratings of these three basic elements. If you see a rating of fertilizer numbers such as 4-4-4 this means it is a balanced fertilizer, having equal proportions of each element. In other words it contains 4% nitrogen, 4% Phosphorus and 4% Potassium. You will want to choose a fertilizer that best suits your needs, often a soil test is a good idea to find out what your soil is lacking, if anything. There are labs that offer this service but you can also buy DIY test kits for a fraction of the cost.

Secondary Macronutrients are other elements required for plant growth and health but are needed in smaller quantities. These elements include calcium, magnesium and sulphur.  Then there are the Micronutrients which are also important but used in very small quantities such as copper, boron, iron, manganese, molybdenum, chlorine and zinc.

Regardless of what fertilizer you use, always follow the directions carefully when diluting and applying. It’s important that plants receive the proper portions of these elements as excesses can be detrimental for their growth.  You don’t want “ too much of a good thing”!