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Worm castings, commonly known as vermicompost, are a remarkable byproduct produced by worms as they break down organic materials, including dead leaves, kitchen scraps, and other organic matter. As worms consume this material, they excrete nutrient-rich droppings that are packed with essential microbes, helping suppress pests and diseases. These castings enhance soil health, promote vigorous plant growth, improve soil structure, and increase moisture retention.
While you can purchase worm castings, creating your own vermicomposting station is easier than you might expect. There are two methods for starting vermicomposting: one is free, and the other is relatively inexpensive. The free method involves attracting worms to your garden soil and beds. To do this, scatter vegetable scraps over the surface of the garden bed. Next, cover the scraps with a layer of clean cardboard or compost, and then add a layer of straw on top. The second method requires building or purchasing a worm bin. After obtaining the bin, you can buy “Red Wiggler” worms from online retailers or local agricultural stores. Add the worms, kitchen scraps, and cardboard to the bin. In about six to eight weeks, your worm castings will be ready for use.
Ahead, experts demonstrate how to incorporate this liquid gold into garden beds.
- Jonathan Russell-Anelli, senior extension associate for the School of Integrative Plant Science, Soil and Crop Sciences Section at Cornell University
- Eric Nieusma, co-owner of Maine Hill Farm, an organic and regenerative grower who farms worms.
Top Dress
The first and easiest way to incorporate worm castings into the garden is to top dress, says Jonathan Russell-Anelli, senior extension associate at Cornell University. Top dressing simply means broadcasting the worm castings on the soil’s surface. “In this case, the grower would be using the casts just like any other fertilizer,” Russell-Anelli says.
Before applying the castings, he recommends conducting a soil nutrient test to determine the application rate. “Keep in mind that this is not a dense fertilizer, and the application rate and timing should be based on the nutrients available in the soil and the plant’s specific needs,” he says.
Most fertilizers contain three key nutrients for plant growth—nitrogen (N), phosphorus (P), and potassium (K). The ratio of each nutrient is referred to as the NPK ratio. Per Russell-Anelli, worm castings typically have an NPK ratio range of 1-0-0 to 5-5-3. “When in doubt, the rule is never adding more than a 1/2-inch of worm casts around your plants,” he says.
To top dress, sprinkle a thin, even layer around the base of your plants, gently working it into the topsoil, and then water thoroughly. As you water, the nutrients will gradually work their way into the soil, feeding your plants over time.
Soil Amendment
Amending soil with worm castings is straightforward. “Similar to most mineral fertilizers, sprinkle a layer of castings on the surface of your garden bed and fork them in at least 2 to 4 inches deep,” explains Eric Nieusma, co-owner of Maine Hill Farm. He points out that the “feeding zone” for most garden plants is within the top 12 inches of soil. However, there’s no need to dig that deep; incorporating the castings just 2 to 4 inches below the surface is sufficient for plants to access these nutrients. “Every time you water or it rains, small amounts of minerals and microbes will be available for the plants to absorb,” Nieusma says.
Seed-Starting Mix
Worm castings are likely the most important amendment in a seed-starting mix, according to Nieusma. “Castings are gentle; they won’t burn plants and provide the perfect low-level fertilization that young plants need,” he says. Additionally, castings supply beneficial microbes in the root zone, which help protect and keep plants healthy. To use worm castings, mix 1 part castings with 4 parts soil, then sow your seeds. This mix will promote better growth, health, and disease resistance in your seedlings.
Vermicompost Tea
Vermicompost tea, also known as worm tea, is a liquid fertilizer created by mixing worm castings with water. The liquid form of vermicompost is a rich soil amendment and is easy to make. In a large bucket, mix 1 cup of worm castings with 1 gallon of water and let it steep for 24 hours. Strain the mixture and pour the liquid on the soil at the base of your plants.
Russell-Anelli notes that a single vermicompost application by itself generally does not provide enough nutrients for an entire growing season, and supplemental or secondary fertility amendments should be applied with fast-growing plants, vegetables, and annuals. Russell-Anelli recommends avoiding this practice before harvest to prevent vermicompost contamination on vegetables or flowers.
Rejuvenate Old Soil
Revitalize your old soil by adding worm castings and watch it come back to life. Start by breaking up any clumps of soil and removing rocks or debris. Then, use a garden fork to aerate the soil. Next, incorporate worm castings into your garden beds; a good ratio is 1 part worm castings to 4 parts soil, which amounts to about 10 to 20 percent of the total volume. Finally, water the garden bed thoroughly to ensure everything is well mixed.