How to Read a Fertilizer Label

Plants, like people, need a balanced diet to thrive. Here is the 'mystery' of fertilizers broken down into its most basic form.


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    Determine percentages of the major active ingredients in the package. N-P-K (Nitrogen- Phosphorus- Potassium) are the 3 most abundant ingredients listed on EVERY fertilizer label. They are always in this order, N-P-K. You will see them on the label as three numbers. Such as: 30-10-10 / 10-5-5 / 21-0-0 But what does it mean and how do you know which formula you need? The first example, 30-10-10, means that if you had 100 pounds of that fertilizer there would be 30 pounds of available nitrogen, 10 pounds of available phosphorus and 10 pounds of available potassium (potash). The remaining 50 pounds are inert or inactive ingredients.
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    Know what each ingredient is used for. Nitrogen is for green and growth. Phosphorus and Potassium for fruit, flower and roots. To turn a lawn green and get it growing, 21-0-0 is the fastest and cheapest way to go. That is Sulphate of Ammonia. However, to promote a healthy lawn that is more drought-tolerant, you would want the roots to be well developed also. A general purpose lawn fertilizer such as 10-6-4 would be a far better diet to achieve a truly healthy lawn.
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    Research your plants needs. Check several sources. Compare notes on what different experts recommend for the type of plants you are growing. When making fertilizer purchases your knowledge of N-P-K percentages will aid in your decisions. Nitrogen = Green/Growth. Phosphorus and Potassium = Fruit/Flower/Roots.


  • One may use a combination of
    • liquid fertilizer for quick uptake and
    • dry kinds that kicks in a little later, and
    • even time-released fertilizers that prolong the benefit to the plants.
  • When reading a fertilizer label you may notice items like: Magnesium, Calcium, Sulfur, Iron, Manganese, Zinc, Boron and Molybdenum in addition to Nitrogen, Phosphorus and Potassium in chemical compounds. These trace elements are essential to the plant's growth. Many of these elements are available in the soil naturally. Plants take in elements (chemicals) through their roots and leaves. Plants convert these raw elements into fruit and foliage, rich in vitamins. Avoid the purchase of additives such as Vitamin B or any so-called fertilizer which contains proteins or fats. Plants can not absorb vitamins, pet food, milk or any processed foods.
  • Well composted vegetation is beneficial to your plant's health because it has been broken down and returned to basic elements for the plant to absorb. Compost also loosens the soil and allows the roots to receive oxygen.
  • Remember: Plants take in elements and convert them into vitamins. Humans take in vitamins and convert them into elements.
  • Fertilizers do not produce instant results. In many cases, it takes two or three weeks for any physical changes to be seen.
  • Components of dry fertilizers may have to break down, and certainly at the very least must dissolve and be kept well enough watered for several weeks to be made continuously available to the roots.
  • As a general rule liquid fertilizers cost much more for the product you receive than their dry equivalent, but they may impact the plant quickly as they are already in a form that is water borne in solution.


  • Do not use fertilizers intended for outdoor use on your houseplants. The chances are very good that fertilizers intended for use on crops, shrubs and trees will be too strong for indoor or small container use.
  • As with any chemicals, be sure to keep fertilizer out of reach of children.
  • Most seedlings do not benefit from fertilizer use. Wait until you feel the plant is old enough (3-4 weeks) to safely apply any fertilizer. When starting to fertilize very young plants do so sparingly.
  • Most plants prefer to have a dormant period in the Fall and Winter. Unless you live in the tropics, stop feeding in the early Fall. New growth at that time of the year is subject to Winter frost damage. Houseplants enjoy having a 'resting' phase as opposed to forcing them to constantly grow.
  • Do not overfeed! When in doubt, use less than recommended, not more. If the label says one cup every month you would be safer to use 1/2 cup every 2 weeks. The same is true with houseplants. They can be fed a weaker solution every time you water instead of a large jolt every month.
  • Do not apply fertilizer directly on the plant, particularly in the hot sun. This can cause leaf burn and damage the plant.

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Categories: Fertilizers