Compost tea made from worm castings is a liquid soil inoculant that offers a significant boost to plant health and soil biology. This brew is created by extracting beneficial microorganisms from the castings into water. The process multiplies the microbial population, delivering a concentrated source of bacteria, fungi, and other beneficial life forms directly to plants and the surrounding soil. Enhancing the microbial diversity of the growing medium supports stronger root development and improves a plant’s natural resilience. Creating this actively aerated tea cultivates a vast population of beneficial microbes, making a small amount of worm castings stretch much further.
Essential Components for Active Brewing
High-quality worm castings are the source of the beneficial microorganisms that will populate the finished tea. The water used for brewing must be non-chlorinated, as chlorine will kill the beneficial organisms. If using tap water, allow it to sit out in an open container for 24 hours to allow the chlorine to off-gas. Dissolved oxygen is mandatory for an active brew, typically provided by an aquarium air pump connected to an air stone submerged in the brewing vessel. Continuous aeration ensures the environment remains aerobic, promoting the multiplication of beneficial bacteria and fungi.
A microbial food source is added to provide energy for the exponential growth of organisms during the brewing process. Common food sources include unsulfured molasses, liquid kelp, or humic acid, which provide simple sugars and nutrients for the microbes. These components are combined in a clean brewing vessel, usually a five-gallon bucket, which should be reserved only for this purpose to prevent contamination.
Step-by-Step Guide to Brewing
The worm castings must be introduced to the water, typically using a handful of castings per five gallons. The castings are usually placed inside a fine mesh bag, such as a paint strainer bag, and suspended in the water. This prevents the tea from becoming sludgy and avoids clogging the air stone.
The microbial food source is then added directly to the water. For a five-gallon batch, one to two tablespoons of unsulfured molasses or a similar liquid feed is sufficient to fuel microbial growth. Activate the air stone and pump, creating a strong, “rolling boil” of bubbles to saturate the water with oxygen.
The ideal temperature for microbial activity is between 60°F and 70°F. Active brewing time is typically 18 to 36 hours; brewing longer can lead to the death of microbes as oxygen and food sources are depleted. The tea is ready when the surface has a light layer of foam and the liquid has a rich, earthy scent. A foul or sour smell indicates anaerobic conditions, meaning the brew has failed and should not be used.
Application and Safe Handling
The finished tea must be used quickly to ensure maximum benefit from the active microbial population. Since aerobic microorganisms die off rapidly once aeration stops, the tea should be applied within four to six hours. It is typically diluted before application, as it is a highly concentrated biological inoculant.
A common dilution ratio is one part finished tea to four to ten parts non-chlorinated water. The tea can be applied either as a soil drench or a foliar spray. Applying it as a soil drench involves pouring the diluted tea directly onto the soil around the base of the plant, introducing microbes to the root zone to improve nutrient uptake and soil structure.
Using it as a foliar spray involves misting the leaves, coating the surface with beneficial microbes that outcompete potential pathogens. When spraying, apply in the late afternoon or on a cloudy day to prevent the sun’s ultraviolet light from degrading the microbes. After application, all brewing equipment should be thoroughly cleaned to prevent residue buildup that could harbor undesirable microorganisms.