Organic garden fertilizers consist of decomposed plant and animal compounds that are broken down by microbes into a form that living plants can use, usually dissolved in water and taken up through the roots. They are naturally occurring chemical compounds, unlike chemical fertilizers that are compounds created in a lab. Some organic fertilizers contain mostly one main nutrient, for example bat guano has high nitrogen content and very small amounts of phosphorus and potassium. Organic fertilizers also contain other nutrients and trace elements. When you select an organic fertilizer, you need to know where it falls on the N-P-K range so you know on what plants it should be used and when in the plant’s life cycle it will offer the most benefit.
What makes good fertilizer?
“N” = Nitrogen, “P” = Phosphorus, “K” = Potassium.
Represented in that order, these are the numbers you find on fertilizer packages. 10-5-5 is an example.
Some plant based organic fertilizers are Compost, Humus, Alfalfa meal, Cottonseed Meal, Corn-gluten meal, Soybean meal, and Kelp/Seaweed products. Check labeling information to be sure that the source plants were raised organically. Some meal crops such as cotton are heavily sprayed with pesticides, and traces of the poisons may be retained in the meal. Compost and humus should be finished, soil-like products when applied to your garden.
Want to make your own compost? Check out our guide here
Animal based organic fertilizers are Manure, Guano, Blood meal, Bone meal, and Fish Emulsion products. Guano may come from bats or seabirds, and is available in pellets or dried powder. Its high nitrogen value makes it quite potent, and it can easily burn plants if not used properly. Fish emulsion is my personal choice, because it is diluted and used when watering plants, or it may be used as a foliar feed. Fish emulsion is gentle enough even for tiny seedlings. It provides all the nutrients they need for a strong start, and is well-rounded enough to use all season. Blood meal is the dried and powdered blood from slaughterhouses, and is a real benefit for green leafy vegetables. Some people say that blood meal attracts dogs; it is also known as a deer repellent. Bone meal is powdered bones and is very high in phosphorus and calcium. Root crops benefit from bone meal, as do flowering bulbs and roses. Broccoli is one vegetable that is reportedly high in calcium, and the only way broccoli plants can get calcium is if the soil they are grown in contains calcium. I dust bone meal in the soil when I set out broccoli plants, and I feel like it increases the health value of my broccoli by increasing the calcium content.
Plants also need minerals. Most mineral fertilizers contain additional micronutrients. Epsom salt is a very good source of magnesium and sulfur. It can be used directly in the soil in granular form, or you can dissolve one Tablespoon of Epsom salt in one gallon of water and spray it on plants for a foliar feeding. Tomatoes, peppers, and roses will really respond to Epsom salt feeding. Greensand, Gypsum, Hard-rock phosphate, Soft-rock phosphate, and Limestone are other mineral fertilizers. A soil test should be done before you add mineral supplements, since some can affect the pH balance of the soil.