Compost Tea

Dawn leads the Compost Tea team

Our volunteers make large batches of compost tea weekly throughout the growing season. This tea is used in our greenhouses and in select spaces around the Discovery Garden.

What Is Compost Tea?

Compost tea is a liquid extract of compost that contains plant growth compounds and beneficial microorganisms. Liquid extracts have been used for hundreds of years in agriculture to promote plant and soil health. These extracts have historically been derived from a wide range of plant materials and animal manures, using a variety of processing methods. Aerated Compost Tea is a more recent concept that incorporates aeration technology to create optimum levels of oxygen for growth and reproduction of beneficial aerobic microorganisms. Compost teas are now being produced and used in large-scale agriculture, viticulture, horticulture, nurseries, lawn care, and residential gardens.

How is it Made?

Compost tea is produced by steeping finished compost in water in order to extract beneficial microorganisms and compounds into solution. It is made in a variety of ways, including with or without aeration, and with or without adding supplemental nutrient sources. Compost tea made with Growing Solutions, Inc. System 25TMuses fine bubble diffusion technology to supply aeration and mixing of the solution, a supplemental nutrient source (Growing Solutions Compost Tea CatalystTM) to feed the microorganisms, and a 24-hour brewing cycle to produce a biologically active, Aerated Compost Tea.

The Right Compost Is Critical!

Compost is the source of organic matter and organisms for extraction, so quality is very important! The quality of the tea is only as good as the compost used to make it. Worm castings are often used alone or blended with compost because of their highly diverse microbial composition. Supplemental nutrients (Compost Tea CatalystTM) are added at the beginning of the brewing process to the tank to encourage the growth and proliferation of diverse aerobic microorganisms that are beneficial to plant growth. Growing Solutions’ Compost Tea CatalystTM contains kelp, humic acids, rock powder and a blend of botanical ingredients formulated for optimal microbial growth and diversity.

Benefits of Compost Tea

Compost tea is a good overall plant health booster. Remember—healthy plants are better able to resist pests and diseases! Compost tea is typically used:

• Provide nutrients for foliar or soil application

• As a microbial inoculant via soil application to help build soil microbial populations

How to Use Compost Tea?

It is best to plan ahead for maximum benefit from compost tea. Aerated compost tea should be used quickly, since it contains living organisms. Ideally, the tea will be used within 4-6 hours of decanting from the brewer. Keeping it cool, out of the sunlight and in an open-top container, can prolong the useful life of the tea. Periodic stirring or continued aeration will prolong its life even longer. Eventually, however, the organisms in the compost tea will consume all of the food and air available to them, causing their populations to rapidly decline. Any tea that is left over or “expired” can be added to the compost pile or to the soil. 

Compost tea can be applied to the soil or directly to the plant as a foliar spray. When it is used as a foliar application, it is best to strive for thorough leaf coverage using a fine mist. Foliar applications are best done early morning or pre-dusk to minimize the effects of UV rays. When used as a soil drench, compost tea should be applied so that it moves into the root zone. This can be accomplished by following the tea application with additional water. Use full strength or dilute1:1 (tea to water) for indoor houseplant and garden plants. Drenching a medium size plant requires about 2 cups of tea plus enough water to get the solution down to the roots. Compost tea can be diluted (up to 1:3 tea to water) to cover a larger area like a lawn. When applying to lawns, apply the tea either just before or just after watering. Apply once or twice a month throughout the growing season.

While it can contain some nutrients and micronutrients, compost tea should not be thought of as a fertilizer. A healthy, biologically diverse soil promotes more efficient nutrient cycling, which can eventually reduce the amount of fertilizer nutrients required. Compost tea should not be viewed as a fungicide or pesticide either. Research has not shown that compost teas can prevent foliar diseases through foliar sprays in a consistent fashion. Compost tea is more accurately described as a soil or foliar inoculant to be used in combination with other good organic gardening practices and inputs.


Use only chemical-free equipment for compost tea storage or applications, e.g. watering cans or sprayers, because residues of fungicides or herbicides are harmful to the compost tea organisms. Similarly, if you are diluting your compost tea before using it, it is best to use water that has been de- chlorinated to maintain the microbial life. Simply storing water in open containers for several hours before diluting the tea will work, as the chlorine will naturally dissipate.