On my weekly visit to The Greenhouse Project, Cory, the greenhouse manager, and I discussed the compost tea he makes and uses on the plants. Compost tea is a mild natural fertilizer that feeds plants and supposedly restores the diversity of beneficial microorganisms in the soil, which helps plants thrive. Many users of compost tea claim that it also works as a foliar spray that reduces plant diseases, but there are multiple peer-reviewed research studies that say there is no data to support that claim. Still, applying compost tea has become a widespread practice on gardens, farms and even in landscape situations.
When plants grow in containers in a soilless mix, they are growing in a contrived situation with few of the benefits of developing in a healthy mineral soil filled with organic matter and beneficial microorganisms. Cory decided to try compost tea in an attempt to add not only fertilizer to the greenhouse plants, but also microorganisms. He came up with a good recipe to make the tea and a system to aerate it.
Here’s the recipe for The Greenhouse Project compost tea.
Two cups of worm castings
One cup of finished compost
1/4 cup of azomite (a silica ore with trace minerals)
1/2 cup of alfalfa meal
One to two tablespoons of mycorrhizal fungi
1/4 cup of liquid kelp
Three to four tablespoons of sugar and water.
Fill a food grade five-gallon bucket with room temperature water and put in an air bubbler for 24 hours. This first 24 hours with the bubbler dechlorinates the water.
Put all the dry ingredients, except for the sugar, into a burlap bag or similar “tea” bag with a stone for weight. Tie the bag shut with twine. Then add the sugar and liquid kelp to the water and stir to dissolve them.
Attach an air diffuser (called an “air stone”) to the bag and “steep” the bag in the bucket to saturate it. Bob the bag up and down whenever you think of it over the course of 24 hours to keep the water and tea mixture more evenly mixed.
Tea should be used immediately after brewing for 24 hours. It can be applied as a foliar spray or soil drench.
The quality of the compost you start with will determine the quality of your end tea product. You can’t have too much air. However, compost tea is not a “silver bullet” for plant health problems caused by poor soil health and improper plant selection and management.
JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at skellyj@unce.unr.edu.