Vermicompost, often referred to as earthworm castings, is a potent organic soil amendment produced by the natural digestive process of earthworms. This dark, crumbly material is rich in microbial life, humic acids, and plant-available nutrients, which are released slowly into the soil. Using vermicompost inoculates the soil with beneficial bacteria, fungi, and plant growth-regulating substances. Application methods vary depending on whether you are preparing new growing mediums, maintaining established plants, or delivering a liquid boost.
Preparing Growing Mediums
Incorporating solid vermicompost into the growing medium before planting ensures young roots have immediate access to a nutrient-dense, biologically active environment. For container gardening and potting mixes, blend one part vermicompost with four to five parts of a standard soil or soilless mix (about 20% concentration by volume). This ratio enhances water retention and provides a steady release of nutrients without overwhelming the plant.
When preparing a specialized seed starting mix, reduce the concentration to prevent germination issues. A lower ratio, typically 10% to 20% of the total volume, is recommended because the high concentration of soluble salts can sometimes inhibit delicate seedlings. Mixing the vermicompost with materials like coir, peat, and perlite helps create an ideal, aerated environment. For large outdoor garden beds, spread vermicompost evenly across the surface before planting, typically a one to three-inch layer. Incorporate this layer into the top few inches of soil using a digging fork or a rake, ensuring the beneficial microbes are distributed throughout the root zone.
Targeted Application for Established Plants
Applying solid vermicompost to established plants provides an effective maintenance feeding boost during the active season. The simplest method is top dressing, which involves sprinkling a thin layer, approximately one-half to one inch deep, onto the soil surface around the base of the plant. Lightly scratch the castings into the top inch of soil after application.
For larger plants or crops in rows, side dressing is preferred. Apply a band of vermicompost around the plant at the edge of the drip line. This places the nutrients where the actively growing feeder roots are located, maximizing nutrient uptake. Thoroughly water the area immediately after application; this helps dissolve soluble nutrients and leach humic substances toward the root system. Re-application is recommended every four to six weeks during the peak growing phase to replenish the microbial population and nutrient supply.
Utilizing Vermicompost Tea
Vermicompost tea is a liquid extract that delivers beneficial microorganisms and water-soluble nutrients directly to the plant roots and foliage. The simplest form is a non-aerated extract, made by steeping a porous bag of vermicompost in water overnight. For a more biologically active product, aerated tea is brewed using an air pump and air stone to encourage the rapid multiplication of aerobic microbes.
A common recipe uses approximately three cups of vermicompost for every five gallons of water. Use chlorine-free water, such as rainwater or water left uncovered for 24 hours, because chlorine destroys the beneficial microbial life. For aerated tea, adding a simple sugar like unsulfured molasses provides a food source for bacteria during the 12 to 24-hour brewing period.
The finished tea can be used as a soil drench, poured directly onto the soil to inoculate the root zone. Alternatively, apply it as a foliar spray, coating the leaves to enhance nutrient absorption and provide a microbial shield. Strain the tea through a fine cloth before using it in a sprayer to prevent nozzle clogging. The finished tea is often diluted with an equal part of water, though it can be used undiluted. For maximum potency, apply the tea immediately, ideally within 24 to 48 hours of brewing, while microbial populations are at their peak activity level.