Feed the soil that feeds your plants. Learn how to make the best organic garden fertilizer with a few simple ingredients, and understand when to apply it for healthy soil and plants.
The organic fertilizer mix recommended by garden guru Edward C. Smith (recipe below) is often thought of as the best organic garden fertilizer. It provides all of the essential macronutrients and many of the micronutrients garden soil needs.
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Before adding any fertilizer, it’s important to have a basic understanding of soil fertility
Plants need several nutrients to grow well. These nutrients are normally divided into two groups: macronutrients and micronutrients.
The macronutrients needed by plants are carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur.
Some common micronutrients needed by plants are boron, copper, iron, manganese, molybdenum, and zinc. Micronutrients are just as important as macronutrients, just needed in smaller amounts.
Which nutrients do I need to provide for my garden?
Although all the macronutrients are important, there are a few that aren’t readily provided by air and water – these are nitrogen, phosphorus, and potassium.
These 3 elements are often used up by growing plants and may need to be replenished. These are the nutrients listed as 3 numbers on fertilization labels N – P – K.
Nitrogen is an important part of the best organic fertilizer
Nitrogen is crucial for healthy leafy growth. Plants use more nitrogen than any other nutrient. Nitrogen is also a key element of chlorophyll.
Plants grown in soil deficient in nitrogen have overall poor plant health. The leaves on nitrogen deficient plants are often light green or yellow.
Too much nitrogen in the soil is also not good for plants. Excess nitrogen may result in excess vegetation without blossoms or fruit. Greens may be bitter when too much nitrogen is present.
Organic sources of nitrogen include: blood meal and fish emulsion.
Phosphorus is an important part of the best organic garden fertilizer
Phosphorus encourages strong root growth. Adequate phosphorus in the soil encourages the development of flowers, fruits, and seeds. Phosphorus also helps plants with photosynthesis. Phosphorus is essential for the plant’s general health and overall vigor.
Plants grown in soil deficient in potassium may have purple leaves. A lack of potassium is also a cause of poor root growth and poor overall plant growth.
Too much phosphorus can inhibit the growth of mycorrhizal fungi – an important soil organism.
Organic sources of phosphorus include rock phosphate, bone meal, and guano.
Potassium is an important part of the best organic garden fertilizer
Potassium increases the yield and quality of plants. This essential macronutrient also helps plants resist disease and stress. Sufficient potassium strengthens root systems and helps prevent wilt. Potassium also helps regulate photosynthesis and aids in the formation of starch. Adequate potassium is crucial for good soil health.
Plants grown in soil deficient in potassium may seem small, weak, or thinner than normal. A lack of potassium is not always easy to spot. Potassium deficient fruits may be small or lack flavor.
Organic sources of potassium include greensand and kelp meal.
The best organic garden fertilizer recipe:
Each batch makes enough to amend 4 cubic foot of soil mix.
1 cup blood meal (nitrogen)
3 tablespoons azomite (trace elements)
1 cup rock phosphate (phosphorus)
1 cup greensand (potassium & trace elements)
Adding a balanced organic fertilizer to your soil mixture for raised beds helps give plants the food they need to grow and thrive in your garden. You are feeding the soil that feeds your plants.
When to use this organic fertilizer mix in your garden
- Mix in when first mixing and adding soil to raised beds.
- Use if needed as an additional feeding for long-season plants (artichokes, eggplant, peppers, tomatoes, squash). Apply and work into the top inch or so of soil; water well.
- Mix into soil before planting each season if needed.
Test soil before adding fertilizer to existing garden beds
A soil test is invaluable for discovering which nutrients your soil is lacking.
Test soil at least once a year to determine nutrient levels. Rather than indiscriminately adding fertilizer, it’s important to fertilize responsibly because too much of any one element can be harmful to plants. Having your soil tested lets you know exactly what is going on in the soil. This is the soil test kit I use.
Soil testing will also help you be aware of your soil pH. Soil pH is a measure of how alkaline or acidic the soil is. The pH scale is from 1-14; 7 is neutral. Values above 7 are alkaline, and below 7 are acidic. One reason pH is important is because if the soil is too acidic or alkaline, some nutrients become unavailable for plants.
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