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What Are Earthworm Castings?

Earthworm castings are a natural wonder, the rich, nutrient-packed byproduct of earthworm digestion. These tiny, soil-like granules are a gardener's gold, offering a sustainable, organic fertilizer that enhances plant growth and soil health. Full of beneficial microbes, they're an eco-friendly boost to any garden. Curious how these castings can transform your garden? Let's dig deeper into their remarkable benefits.
Christina Edwards
Christina Edwards

Earthworm castings are the remains leftover after an earthworm has digested organic matter. This material is often used an organic plant food because of its high nutrient content. Earthworm casting are typically produced by adding several earthworms to piles of organic matter. The castings are then separated and used as fertilizer.

After the organic matter enters the earthworm's mouth, it then passes through the rest of the digestive tract. Tiny grains of dirt and sand act as teeth, helping the worm break up larger particles before the matter passes through the pharynx. From there, the organic matter then passes through the esophagus, into the gizzard, then into the intestine. After passing through the intestine, it will then pass out of the worm's anus, resulting in earthworm castings.


Each step of digestion either physically or chemically alters the organic matter. For example, the pharynx secretes mucus, which helps the matter pass through the esophagus easier. In the esophagus, calcium carbonate is added, and the gizzard mashes the matter together, creating a thick paste. By the time the worm castings are created, several vital nutrients have been added, including nitrogen, potassium, phosphorus, and magnesium.

Earthworm castings have a high nutrient content.
Earthworm castings have a high nutrient content.

These nutrients are of the main reasons that earthworm castings make such great fertilizer for many plants. Each of the nutrients — especially nitrogen, potassium, and phosphorus — is essential to plant growth. Nitrogen is needed to produce lush, green foliage, and speedy growth. Phosphorus, on the other hand, is necessary in order to help turn the rays of the sun into chemical energy.

Nutrients in earthworm casting are also released a little at a time. This is because they are surrounded by a mucus membrane, or oils. These membranes slowly wear away, and thereby time release the nutrients into the soil. Unlike many commercial fertilizers, this will not cause fertilizer burn.

The texture of earthworm casting is also beneficial. Although it does help retain much needed moisture in the soil, it also helps the soil around a plant drain properly. This action can help prevent the roots of a plant from becoming waterlogged, which can help prevent root rot.

As a fertilizer, earthworm castings can be added to the soil in a few ways. First, it can be mixed in with existing soil or sand. Some people may choose to simply sprinkle it around the bases of plants. It can also be mixed with water and sprayed onto a garden or other area that needs fertilized.

These castings can be quite expensive to purchase commercially. Many people who want to use this type of organic fertilizer can often make it at home. This can be done by creating a compost pile or bin. Adding small bits of organic matter, such as food scraps and grass clippings, to the pile every once in awhile can result in a large amount of earthworm castings over time.

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    • Earthworms.
      By: Dusty Cline
    • Earthworm castings have a high nutrient content.
      By: zest_marina
      Earthworm castings have a high nutrient content.