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The First Time Gardener: Understanding Fertilizers

FertilizingI don’t know about you, but going into the fertilizer and chemical section of a garden center can be a daunting experience. Even though I am knowledgable about fertilizers and I always go in knowing what I need, it can still be hard to find what I want. All the swirling colors and confusing slogans make it hard to figure out what I should be buying!

So if it is hard for me, how should a new gardener figure out what to buy? Here are some keys to understanding fertilizers:

  1. Those numbers on the bag mean something. 25-4-6 is not some kind of secret code, but rather your key to know what is in the bag. The numbers stand for Nitrogen-Phosphorus-Potassium (N-P-K), the three most important nutrients your plants need.
  2. The numbers refer to the percentage of nutrient. So a 25-4-6 fertilizer is 25% Nitrogen, 4% Phosphorus, and 6% Potassium.
  3. Synthetic vs. organic fertilizers. Synthetic fertilizers are usually mined and processed rock or a chemically synthesized form. (Nitrogen frequently is a petroleum by-product.) Organic fertilizers come from an organic source (decomposed or processed plant or animal matter, such as bloodmeal or bonemeal). Both types are good fertilizers, but organic fertilizers are frequently more expensive.
  4. Vegetables need a lot of nitrogen, phosphorus, and potassium. However, that doesn’t necessarily mean you need a balanced fertilizer, such as a 10-10-10. You should take a soil test to determine if your soil is deficient in phosphorus or potassium. Why apply a fertilizer if you don’t need it?
  5. Liquid or granular? You can buy a granular fertilizer that you incorporate into the soil before planting or sidedress (sprinkle around the plants on the soil surface) after planting. You can also buy a fertilizer that you mix with water and apply regularly throughout the growing season. It really depends on what you find easiest.
  6. “Extras”. For your vegetable garden, do NOT buy a fertilizer that also contains an insecticide or herbicide. Those products are not meant to be used for edible crops.
  7. Can I use manure? Compost and well-composted manures are great for your garden, both as a source of organic matter and as a source of nutrients. (Manure should be composted. If using raw manure, you should wait 180 days before harvesting any produce from that garden.) However, it is hard to know exactly how much of any given nutrient compost or manures contain.