What to Know About Fertilizer

April is the time for planting! You will be planting most of your first succession veggies around this time. And with that comes fertilizer. Fertilizer is a key component to a successful garden and for crop health. 

What we’ll cover:

  • How to read a bag of fertilizer
  • Importance of Nitrogen, Phosphorous, and Potassium
  • Organic vs Synthetic/Conventional
  • How to add fertilizer to your garden

Let’s start with reading a bag of fertilizer. This is crucial to know how to do because it will tell you how much of each element the bag contains, which will in turn be important for giving your soil what it needs. 

  1. On each bag of fertilizer, there will be a number such as this: 5-4-3. This represents the percentage of Nitrogen-Phosphorus-Potassium (N-P-K) in the bag. For example, 5-4-3 means it’s 5% Nitrogen, 4% Phosphorus, and 3% Potassium by weight.
  2. Nitrogen is for leaf growth, phosphorus for root growth, and potassium for fruiting bodies.

 Organic vs. Synthetic/Conventional

        • Synthetic/Conventional fertilizers are made out of highly processed materials that often are fossil fuel by-products.  They are fast acting and leach from the soil quickly, meaning you must reapply them throughout the growing season. Synthetic fertilizers often just contain the macro-nutrients NPK and nothing else.
        • Organic fertilizers, on the other hand, are made from less processed ingredients like manure, bone meal, fish meal, and rock minerals.  They are slower releasing and provide a steady stream of nutrients to your crops throughout the season. Organic fertilizers often contain a variety of micro-nutrients as well, such as magnesium, calcium, sulfur, iron and zinc.
        • If you need more nitrogen, phosphorous, or potassium directly, you can use the following:
          • Organic sources of Nitrogen: alfalfa meal, blood meal, feather meal, fish meal, cottonseed meal
          • Organic sources of Phosphorus: bone meal, rock phosphate
          • Organic sources of Potassium: green-sand, sunflower hull ash

Reading a Soil Test

Often, soil tests give their recommendations for conventional fertilizer.  To convert to organic fertilizers, which don’t provide such concentrated forms of nutrients, you’ll need to do a little math.  

  • Remember that the numbers listed on a bag of fertilizer are percentages. 
  • If a soil test tells you that you need to add 1 lb of nitrogen per 1,000 square feet of garden, then you need to divide 1 by the first number on your bag.  For conventional fertilizer, this might be 25%, so that would be 1 / 0.25 which equals 4 lbs. For organic, this might be 5%, so that would be 1 / 0.05 which equals 20 lbs.


Harmony 5-4-3 Fertilizer

This is the fertilizer we use and hand out to our participants as it is a great all purpose organic fertilizer. If interested, you can buy it here. Below are some tips to using it correctly:

  • Use 6-8 lbs per 100 square feet
    • This equals 15-20 cups per 100 square feet
    • Or 2 tablespoons per square foot
  • Don’t scatter fertilizer around your whole garden. This will only feed the weeds.
  • Put fertilizer directly into the planting hole or seed trench for best results.


These are just a few recommendations. Feel free to choose what’s best for you and your garden. As always, happy planting!