Organic fertilisers — which kind should you use?

When you’re moving into organic farming, you’re going to need to find alternative fertiliser sources than the commonly used chemical fertilisers. When it comes time to use your spreading equipment, you want to be confident that your fertiliser choice will be effective in stimulating growth in your crops. Once you have had your soil tested, you should have a good idea about the kinds of nutrients that your soil will need.

Here’s a run-down of some of the most commonly used organic fertilisers and their benefits:

Bone meal

Bone meal is a by-product from slaughtered animals. The bones are usually process by steam processing and crushing.

Bone meal is a good source of phosphorus and calcium. Bone meal is a slow release fertiliser, taking a few months for the nutrients to become available to the plants.


The nutrients present in manure can vary depending on the source animal. Raw manure can be dangerous to use, due to the pathogens that can be present. As such, manure should by composted or aged for 6 months.

Manure provide both macro- and trace nutrients, and contain the three key nutrients, nitrogen, phosphorus and potassium. Manure is a slow release fertiliser — only half of the manure’s nitrogen is made available to plants within a year of it being laid. One downside of manure is that it can contain seeds of weeds.


Compost typically consists of broken down plant matter. Using compost will provide soil with large amounts of organic matter and micronutrients, which are highly beneficial to soil fertility. Topsoil treated with compost can find its soil retention increased.

Since compost can vary widely, care should be taken to ensure that the compost is broken down properly, and does not contain too many salts, which can lead to plant burn.

Cottonseed meal

Cottonseed meal is a by-product of the cotton plant, and is very rich in nitrogen. Care should be taken when using cottonseed for organic farming — a lot of cotton is genetically modified. Typically, GM cotton crops are treated with a lot of pesticides, which may find their way into your soil.

Cottonseed meal takes several months to break down and make its nutrients available to your crops.

Fish emulsion

Fish emulsion fertilisers are among the strongest smelling fertiliser options, but also one of the richest sources of the three key macronutrients, nitrogen, phosphorus, and potassium. These fertilisers are usually created with heat treatments from industrial fish by-products.

Liquid kelp

Liquid kelp fertilisers contain low amounts of the three major macronutrients, but are excellent sources of trace nutrients as well as plant growth hormones. Unlike other organic fertilisers, the nutrients in liquid kelp fertilisers are available immediately.