10 Best Organic Fertilizers

Neptune's Harvest CS650 Organic Crab Shell Plant Food is a dry organic fertilizer made primarily from crab shells, which is a natural source of calcium and magnesium along with nitrogen, phosphorus, and potassium (N-P-K ratio of 5-3-0). This means it provides moderate nitrogen and phosphorus but no potassium, making it especially useful if your soil needs calcium and minor nutrients rather than a balanced NPK boost. Because it’s a shell-based product, the nutrients release slowly as the shells break down, offering a gradual feeding effect rather than a quick nutrient rush. This slower release is good for steady, long-term soil improvement but not ideal if you want fast results.

The fertilizer is granular, which makes it easy to spread in the garden and mix with other soil amendments like kelp meal to improve moisture retention and organic matter. One notable benefit is its ability to help control nematode and fungus problems, which can protect plant roots naturally. While it does provide some micronutrients, it lacks a broader spectrum of additives or certifications that some organic fertilizers offer. Also, it does not contain potassium, so you may need to supplement if your plants require it.

The product is fairly heavy and comes in a large 50-pound bag, making it better suited for gardeners with larger spaces or those who want a long-lasting supply. This fertilizer is a solid choice for an organic source of calcium and nitrogen with slow nutrient release and some added pest control benefits, but it is less suited for quick nutrient fixes or balanced NPK feeding.

Charlie Carp Natural Pellet Fertiliser is an all-purpose organic fertilizer made from sustainably sourced European carp, which is a unique and eco-friendly source. It comes in pellet form, making it easy to apply by simply scattering around your plants. The pellets offer a slow release of nutrients over three months, so you don’t need to frequently reapply, which is great for busy gardeners or indoor plant keepers.

This slow release helps provide steady nourishment to plants and supports soil health by encouraging earthworms and moisture retention. The fertilizer is rich in protein and contains natural fish oil, which may contribute beneficial micronutrients and help deter pests. Importantly, it is odourless, avoiding the fishy smell often associated with organic fish-based fertilizers.

It is a convenient, sustainable choice suitable for gardeners looking for an easy-to-use natural product to support general plant growth and soil conditioning without unpleasant smells.

Searles 5 in 1 Organic Fertiliser Pellets come as easy-to-use granules, which many gardeners find convenient for spreading in various types of gardens. This product stands out by being fully organic and BFA registered, giving confidence it contains natural ingredients without synthetic additives. It’s designed to promote strong plant growth, vibrant flowers, and healthy fruits and vegetables, thanks to its premium blend of natural materials.

The pellets also help build humus in the soil, encouraging beneficial earthworm and microbial activity, which is great for long-term soil health. Being granular, it’s best suited for outdoor gardens rather than quick indoor plant feeding, and the 2.5 kg size is practical for medium-sized areas.

This product is a solid choice for gardeners wanting a natural, multi-purpose fertilizer that improves soil quality while supporting plant growth, especially if you prefer organic options.