The substance often referred to as “worm poop” is beneficial for plants. This end product of earthworm digestion is scientifically known as worm castings or vermicompost. Worm castings are a valued soil amendment created when earthworms consume and process organic matter, resulting in a dark, nutrient-rich material. This natural process transforms decaying matter into a form that plants can readily absorb.
The Nutritional Advantage of Worm Castings
Worm castings offer significant plant nutrition due to their unique, highly bioavailable structure. The earthworm’s digestive tract converts nutrients like Nitrogen, Phosphorus, and Potassium (NPK) into water-soluble forms immediately accessible to plant roots. This is unlike synthetic fertilizers that require complex breakdown processes. This structure also ensures a slow-release mechanism, providing consistent nourishment without the risk of “fertilizer burn.”
Vermicompost is a biological amendment containing beneficial microorganisms, including bacteria and fungi. These microbes continuously break down organic matter and cycle nutrients into forms the plant can absorb. Castings also contain plant growth-promoting hormones, such as auxins and gibberellins, which stimulate robust root development and overall plant growth.
Enhancing Soil Health and Water Retention
The physical contribution of worm castings to soil structure is significant. Castings are coated in a mucus layer that binds fine soil particles into stable aggregates. This process transforms dense or sandy soil into a crumbly, porous texture necessary for healthy root growth.
Improved soil aggregation enhances aeration and drainage, preventing roots from becoming waterlogged. The porous structure also increases the soil’s capacity to hold moisture. Soil amended with worm castings can retain significantly more water, potentially reducing the need for frequent watering. This dual action of improving both drainage and water retention makes castings effective in various soil types.
Methods for Applying Worm Castings
Applying worm castings is straightforward, and the method depends on the gardener’s goal, whether feeding an established plant or preparing a new bed.
Top Dressing
This method involves sprinkling the castings directly onto the soil surface around the base of an existing plant. A handful or two around the stem is adequate, or a thin layer of about half an inch can be spread across the entire planting area. The nutrients and microbes filter down into the root zone every time the plant is watered.
Soil Amendment
This is the preferred method for starting plants or rejuvenating containers. It involves mixing the castings thoroughly into the planting medium before use. A ratio of 1 part castings to 5 parts soil (10% to 20% by volume) is generally recommended for optimal results. Mixing castings into the soil ensures the roots are surrounded by nutrients and beneficial biology immediately.
Compost Tea
This liquid feed is made by steeping the castings in water. A basic recipe involves soaking one part castings in three parts dechlorinated water overnight. Dechlorinated water is necessary because chlorine can harm the beneficial microbes. For a highly concentrated microbial solution, an aquarium air pump can be used to actively aerate the tea for 24 to 48 hours, often with molasses added as microbe food. This liquid can be applied as a soil drench to inoculate the root zone or as a foliar spray to help suppress plant diseases.