Learn about that dark liquid (worm leachate) seeping out of your worm bin and how to use it safely

Worm leachate is the dark liquid that leaks out of the bottom of your worm composting bin. Leachate is water released from the cells of decomposing food scraps.

How is worm leachate different from worm compost tea?

Worm bin leachate is not the same as worm compost tea. Worm compost tea is a tea made from steeping (or brewing) vermicompost instead of tea leaves. It isn’t appetizing for you but your plants will love it! The nutrients and beneficial microbes in the worm compost diffuse into the water making liquid fertilizer for your plants. Some gardeners refer to compost tea as ‘liquid gold’ because it is such a powerful organic fertilizer for any plant. Worm compost tea is aerobic (with oxygen) whereas worm bin leachate is anaerobic (without oxygen).

Is worm bin leachate safe to use on plants?

The digestive tract of a composting worm is really good at removing harmful pathogens. Unfortunately, leachate is usually not consumed by your composting worms and therefore does not get cleaned by going through a healthy worm gut. Worm bin leachate can potentially contain toxins that are harmful to people. Because of the risk of harmful pathogens, I do not recommend using raw worm bin leachate on edible plants.

How can you use worm leachate?

Even with the risk of potentially harmful pathogens there are a few ways you can use worm bin leachate to benefit your plants.

1. Never use foul smelling worm leachate. This can be a sign of contamination. Discard any nasty smelling worm leachate in the trash or down the drain.
2. If possible, add some oxygen. Aerate your worm leachate with a bubbler from a fish tank.
3. Use worm leachate on non edible plants like flowers, trees, and bushes. Your plants will still benefit from the worm leachate but you won’t have the risk of eventually eating any harmful pathogens.
4. Dilute your worm bin leachate with water. I use the ratio: one part worm leachate to two parts water.
5. Pour your worm composting leachate on your hot compost pile. If you manage your compost pile correctly it will heat up enough to kill off any harmful bacteria.

Is your worm bin producing LOTS of worm leachate?

Too much worm bin leachate is a sign that your worm bin conditions are out of balance. You should not have to drain the leachate every day. If you do, try adding more dry bedding and feeding less food scraps.