Fertilizers: Understanding N-P-K value

When looking at fertilizer packages, most companies will list the NPK value shown something like this: 10-10-10, 10-20-0, 20-10-15, etc. These numbers represent the macro-nutrients: nitrogen(N), phosphorus(P), and potassium(K). The higher the number, the greater the concentration of the nutrient, as the numbers themselves represent the percentage of each nutrient by weight. 

  • Nitrogen (N) is useful to plants by helping with the production of foliage and promotes rapid growth.
  • Phosphorus (P) promotes root growth, flower development, and fruit production.
  • Potassium (K) helps with the overall function of the plant, helps prevent diseases and cold/heat damage. 

For most houseplants, the standard 1:1:1 dose works great. Higher phosphorus (P) doesn’t always mean more flowers. The overall health of a plant will determine how much flower it will produce for plants that flower more than just once in their life cycle (polycarpic plants). The overall health and environment should be considered when growing plants for flowers. 

Important note: Follow all manufacturers’ instructions. Fertilizer burn can occur if improperly used. Having drainage holes in your pots and flushing through with properly pH adjusted water between feedings can help manage these issues if you notice signs of distress in your plants after giving nutrients. It is also important to know when your plant’s growing cycle is, as some plants will be summer dormant and others can be winter dormant. It is not a good idea to fertilize when your plants are dormant and not actively growing or using nutrients.