How to Make Compost Tea

Give your garden the benefits of compost and organic fertilizer with less work by brewing and using compost tea.
Brewing Compost Tea

Brewing Compost Tea

Strain water-filled compost through cheesecloth to make compost tea, a soil-enhancing liquid for watering garden plants.

Photo by: DK - Ready Set Grow! © 2010 Dorling Kindersley Limited

DK - Ready Set Grow! , 2010 Dorling Kindersley Limited

Compost teas are a great way to give your garden some of the same benefits you’d get from adding compost without having to shovel and cart heavy compost around the yard. Like compost, compost tea (when brewed correctly) is brimming with beneficial bacteria, fungi, nematodes and nutrients. For instance, one teaspoon of compost tea may contain up to 4 billion (good) bacteria! This fantastic concoction does wonders in the landscape when applied to a plant’s leaves and the root zone or to the soil in general.

Healthy Leaves

Did you know that bacteria and fungi live on plant leaves? The foliar bacteria and fungi that are most familiar to gardeners tend to be undesirable diseases and pathogens, like powdery mildew or leaf spot. Although a fungicide or other pesticide treatment can help clear up or stop the spread of the bad microorganisms, these treatments also kill the beneficial bacteria and fungi that live on the leaf surface.

One would think that sterile foliage would be a good thing, but it actually isn’t. When leaves are covered with the sort of beneficial bacteria and fungi that are found in compost tea, there’s more competition for resources and less space for undesirable microbes to take hold. Rather than treating diseases with fungicides after they’ve already taken hold, consider applying compost tea to foliage preventatively at the beginning of the growing season.

Properly brewed compost tea shouldn’t burn leaves. However, the ultraviolet (UV) rays in sunshine can kill the microorganisms; so it’s best to apply before 10 a.m. or after 3 p.m. during the long days of summer. A standard garden pump or backpack sprayer can be used, although a concrete sprayer will be just as effective and better able to handle the occasional solids that make it through a strainer. It’s fine to dilute compost tea as long as the water used is free of chlorine (which would kill the beneficial organisms in the tea). Apply liberally to the top and bottom of leaves.

Healthy Roots

Drenching with compost tea is a great way to quickly deliver organic fertilizer and beneficial organisms from compost to a plant’s root zone. Simply pour the tea mixture to the soil in the area below the plant’s leaves (or under the “drip line”). The liquid tea will carry beneficial bacteria, fungi and other microorganisms down to the area around the roots. 

Once there, the bacteria will help unlock nutrients that are already in the soil but were previously in a state the plants couldn’t use (ex. converting unusable ammonium nitrogen to nitrite, then to useable nitrate). The mycorrhizal fungi will create a symbiotic relationship with plant roots that will benefit both the fungus and the plant. In exchange for some of the carbon in the roots, mycorrhizae will extend further into the soil to bring back nutrients for the plant. Some estimates suggest that mycorrhizal fungi can extend a plant’s reach in the soil by 95%!

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