What’s in that tank?

While out in the park this fall, you may notice our truck with its spray tank filled with a brown liquid and think, “what is that”? Immediately, some of you would assume it’s some sort of chemical. Fear not though, it’s completely safe and organic! The Esplanade Association manages its horticulture program exclusively through organic techniques. One of the tools available in an organic program to address soil fertility and overall plant health is the use of compost tea.

So that begs the question, “what IS compost tea?

The short answer is: A special brew of compost and water and other ingredients. Compost tea helps increase the soil’s biodiversity and improves plant health as a result.

The more detailed explanation is: It’s an brew of beneficial soil microorganisms derived from compost and applied in a liquid form. Natural processes provide all plants the nutrients needed to grow and thrive. These processes include the decomposition of organic material and microorganism interaction with mineral components in the soil. Compost tea is the means to replicate the biology which provide these services in a managed landscape.

As you can imagine, not all plants require the same levels and concentrations of nutrients. To address different plant types, we create different brews: bacterial, fungal, and a combination of the two. The compost used to create the tea must first be ‘healthy’, meaning it contains a diverse biological community. The compost we use is created here on the Esplanade with plant material we remove from the park. This compost can then be ‘activated’ prior to brewing by adding foods such as molasses or kelp. The compost is supplemented with kelp meal, azomite (a mineral), and vermicompost (worm manure). This mixture is then placed in a special bag which attaches to an aerator inside the brewer filled with decanted water (municipal water contains chlorine which kills some of the biologic populations).

The aeration of the tea is critical for the success of the brew. Our staff look to encourage the development of aerobic microorganisms which rely on oxygen rather than anaerobic organisms which could be harmful to the plants. Ingredients are added to the tank and either brewed for 18-36 hours for a bacterial brew or 36-48 hours for a fungal brew.

Once the brew is complete, it’s transferred into our spray tank and must be applied throughout the park within hours of being brewed.  Compost tea has a relatively short shelf life due to it being comprised of living organisms which require both food and a constant source of oxygen.

Now when you see the truck out in the park with brown liquid in the tank, you’ll know it’s compost tea, and maybe impress a fellow curious park-goer with this new knowledge!

Written by Organic Land Care Horticulturist Eric DiTommaso

Eric DiTommaso spraying compost tea in the park.