Fish emulsion, bone meal, blood meal, manure and compost all work well and they’re organic.
Overview of organic fertilizers
To be called ‘organic’ means it occurs in nature, the three ‘natural’ categories are animal-based, plant-based and mineral-based organic fertilizers. The bottom line – organic fertilizers feed the plants while adding organic matter to the soil. Soil that is rich in organic content holds moisture well and promotes the growth of beneficial organisms that live in the soil and improve the health of the plant’s root systems.
Basic properties of organic fertilizers
- Fish Products – the by-products of fish are great fertilizer and available as emulsions (from fermented fish remains) plus they provide a combination of nitrogen, phosphorus and potassium and trace elements good for the soil. Fish fertilizers are safe for the new roots of seedlings. Kelp and seaweed is sometimes added to fish fertilizers for additional nutritional value.
- Blood Meal – from powdered animal blood, contains nitrogen and lots of micronutrients and great for leafy green plants like lettuce.
- Bone Meal – from animal and fish bones, high in calcium and phosphorus and usually comes in powdered form.
- Manure – animal manure adds lots of good organic matter to soil. Chicken manure, although high in nitrogen is better when composted as it can burn tender plant roots.
- Bat and Seabird guano – bat and seabird poo is generally made into pellets or powder and like chicken manure is high in nitrogen and could be hard on young plant roots.
Plant fertilizers tend to have low to moderate nitrogen, phosphorus and potassium (N-P-K) but once placed in the soil the plants use them quickly. Micronutrients and trace minerals may also be present in plant-based fertilizers.
- Compost – the best thing to do with compost is to add it to the garden and flowerbeds, it adds great organic matter to soil.
- Alfalfa meal – adds nitrogen, potassium and trace minerals to soil. Roses love alfalfa meal and when added to the compost pile it speeds up the process!
- Corn gluten meal – this fertilizer is great for the greenest of lawns in spring and it tends to prevent weed growth. It’s hard on new seedlings however and not recommended for plants until they are established.
- Soybean meal – similar to alfalfa meal, high in nitrogen and phosphorus, and roses love it too.
- Cottonseed meal – high in nitrogen and potassium, for organic gardening look for organic cottonseed that has not been treated with pesticides that can remain in the cottonseed oils.
- Kelp / Seaweed – low in nitrogen, phosphorus and potassium but adds valuable vitamins and micronutrients to soil.
- Humus – also knows as humic acid and humates, are not so much fertilizers as they are soil stimulants that encourage microbial life which in turn supports plants. Humus is best used as a soil supplement.
An application of most mineral based fertilizer usually lasts awhile as they break down slowly in the organic garden. Some take months and some years until they are sufficiently broken down and used by the plants.
- Limestone – is commonly used to boost soil pH. There’s dolomitic limestone high in calcium and magnesium, and calcitic limestone that is high in calcium carbonate. Before adding limestone, have a soil test done to determine which limestone to add.
- Hard rock phosphate – best used with the intent to add phosphorous over the long-term and it can also raise the soil pH
- Soft rock phosphate – contains less calcium and phosphorous than hard rock phosphate plus it has many micronutrients, breaks down very slowly and an application can last for years.
- Gypsum – contains calcium and sulfur and will add calcium to the soil without affecting the pH.
- Greensand – breaks down very slowly and is mainly used to build up the soil’s long-term reserves of potassium.
- Chilean nitrate of soda – fast acting and soluble in water, high in nitrogen but also in sodium so avoid adding to salt sensitive plants.
- Epsom salt – Roses and peppers love Epsom salt. It’s absorbed quickly when a tablespoonful is mixed with a gallon of water and sprayed on garden plants. Epsom salt contains sulfur and magnesium and may also be added to the soil in granular form.
Tips about fertilizers
- Fertilizer blends high in nitrogen and low in phosphorous will inhibit flower production.
- High nitrogen content fertilizers are recommended for leafy vegetables and turf grasses where you want more green and less flowering.
- Vegetable and fruit crops need higher levels of phosphorous
- On the fertilizer label nitrogen (N) is first, phosphorous (P) is next and potassium (K) is third (N-P-K)
Additional resources: Fertilizing your Organic Garden for Dummies and Wikipedia: organic fertilizer. Photo credit: Microsoft clipart