fertilizer compost on a grassy hill

What is it?

Fertilizers are compounds given to plants to promote growth. Fertilizers can be organic (from natural materials) or inorganic (from manmade, inorganic sources). Fertilizers can come in many different states, including granular, liquid, controlled release and tablets.

What the Numbers Mean

On a package of fertilizer you will find three numbers separated by hyphens. The numbers indicate the percentage of nitrogen (N), phosphorus (P), and potassium (K, Aka potash). A "complete" fertilizer contains nitrogen, phosphorus and potassium.

What they do...


lack of nitrogen on corn leaf, edges turning brownNitrogen is required for the green, leafy vegetative growth of plants. Nitrogen is easily leached down through the soil below the roots and is not available to the plant so it is the element most often lacking and needing replacement. Too much nitrogen can delay flowering, fruiting and seed set. It is the most important plant nutrient.

Deficiency symptoms of nitrogen are an overall pale yellow color of leaves and dwarfed or stunted plants.

Nitrogen leaches out of the soil very quickly and that is the reason that it is usually the highest percentage in most fertilizers.


Phosphorus promotes root growth; root branching, stem growth, flowering, fruiting, seed formation and maturation.

Deficiency symptoms are indicated by a red or purplish tinge to stems and foliage...

yellowing of leaf from phosphorus deficiency
purple margins on leaf from phosphorus deficiency


scorched looking leaves due to potassium deficiencyPotassium enables the plant to withstand stress such as drought, cold, heat, and disease. It also stimulates flower color and promotes tuber formation and a strong root system. Phosphorus and Potassium do not leach through the soil like Nitrogen does so when planting flowers it is recommended that you put the fertilizer in the bottom of the hole so it is available to the plants roots.

Deficiency symptoms are indicated when the leaves appear dry and scorched on the edges and have irregular yellowing.