Understanding Compost Tea

Often, when I discuss composting with homeowners, the basics of production, application, and utilization are more than enough to fill an hour’s worth of conversation. Between what can and should be composted, how to layer those components, how to feed and turn the pile, and then finally, how to utilize the finished compost –there is a lot to discuss. However, one other slightly less common yet highly beneficial component to composting also exists: compost tea. Utilized correctly, this homemade “liquid fertilizer” can boost crop production noticeably by introducing beneficial microorganisms to the soil, encouraging healthier and larger crops as nutrients are made available for absorption.

So, what is compost tea, and how is it made?

Though the idea of compost tea may conjure images of wacky backyard chemistry experiments or the brewing of complicated elixirs, the truth is much simpler. Compost tea is nothing more than a large ‘tea bag’ filled with finished compost steeped in water. The process entails placing finished compost into a cloth bag (often a pillowcase) and submerging it in a large bucket of water. The compost bag is then left in the water long enough for the beneficial microorganisms within the compost to be released into the water, creating a nutrient-and-microorganisms -dense liquid. Ideally, this steeping will last at least 24-48 hours, allowing ample time for microorganisms to infuse. Once steeped, the bag can be wrung out of liquid, and the remaining compost matter within the bag can be added to the garden. The one caveat to this process is that if an air stone is used in the water while steeping, a thicker concentration of microorganisms will likely be generated in the tea.

Now with a finished compost tea ready to be used, it’s important to understand how it works. Compost, in general (not the tea), functions by supporting the hundreds of millions of microorganisms that break down organic material into humus –a substance that, when added to soil, helps “unlock” available nutrients, making them better accessible to plants. Compost tea skips the step of needing physical humus incorporated, instead removing the microorganisms from the compost and allowing them to ultimately have the same nutrient-release soil effect by being applied directly.

The application of compost tea can be as liberal or conservative as one prefers –bearing in mind that most benefits come from the microorganisms rather than physically present nutrients. Applied to a garden plot, the soil is then left with a healthier overall biome, where plants are healthier, better supported, and more resilient. Ultimately, this results in larger plants and better-quality crops for harvest. ‘Burning a plant,’ which is possible with excess nutrients, is not a concern with excess microorganisms.

However, remember that the same components used to construct the compost are utilized in your compost tea. Composted manure, for example, is often very high in nutrients and could potentially harm plants if overapplied. For a typical ‘yard-and-table scraps’ compost, feel free to apply away with your tea!

by Anthony Reardon, Horticulture Small Farms Agent, 2025