Plant Food - Edmonton Horticultural Society

by Colleen McKenna

Your plants need food. This food, called fertilizer, consists of a variety of nutrients and minerals. Too much or too little of any one nutrient will cause problems. The primary ingredients of any fertilizer are N-P-K and you’ll see a series of numbers (for example, 10-10-10) representing the proportions of these elements on almost every garden soil amendment or fertilizer. What does this stand for?


  • N – nitrogen, which promotes foliage production
  • P – phosphorus, which promotes root growth
  • K – potassium, which aids in flower and fruit production


  • Magnesium
  • Calcium
  • Sulfur
  • Iron
  • Manganese
  • Zinc
  • Boron
  • Molybdenum

While all of the micronutrients are important, you don’t normally need to be concerned about them, as any good fertilizer will provide sufficient amounts.

What about the terms organic and inorganic? These just refer to the source of the fertilizer. Inorganic fertilizers are usually synthetic or man-made, tend to have higher concentration of nutrients, and can be either slow or fast release. Organic fertilizers are sourced from natural sources such as manure and compost. They have lower concentrations of nutrients and are released slowly.

Is there a difference between the two to the plants? No, because nitrogen is nitrogen to a plant. However, synthetic fertilizers, when over applied, can run off into the sewer system, and the excess nitrogen can cause algae blooms in water systems. Fertilizer that runs off is wasted, which also causes unnecessary expense to the gardener. Be aware of this when you apply your fertilizers, and only apply at the recommended rate.