How to Make Compost Tea

Photo: Alison Hancock/Shutterstock.

For many people, a freshly brewed cup of tea is one of life’s simple pleasures. For the plants in your garden, it can be so much more.

No, not oolong tea. Or black tea. Or green tea. We're talking about compost tea.

Compost tea is an organic, low-strength, nutritionally rich, liquid fertilizer. Any gardener with a compost pile can brew a batch by steeping aged compost in water. Think of it as an energy drink for your plants that you can give them anytime of the year.

It’s more effective than compost for feeding plants because the brewing process “harnesses beneficial bacteria in the compost,” said Suki Janssen, waste reduction administrator for the Athens-Clarke County Recycling Division in Athens, Georgia.

“Microbes such as bacteria can become inactive in compost because the compost may lack nitrogen for the bacteria to eat,” Janssen explained. “In making compost tea, you feed the bacteria, which causes them to become active again. Freshly active microbes have fertilizer benefits for plants.”

In some cases, the tea-brewing process can cause nutrients and beneficial bacteria and fungi to multiply. They become suspended in the water in a form that makes them quickly available to plants.

The key to deriving the full garden benefits of compost tea is to use the compost tea within 24 hours of completing the brewing process. “Compost tea has a very short shelf life in which the energized microbes will remain active,” Janssen pointed out.

Here is an easy, six-step compost tea recipe that Janssen likes (from the Home Composting Made Easy website). All you need are two buckets, a shovel, fresh finished compost, water and a straining cloth such as cheesecloth, burlap or even an old shirt.

Step 1: Fill a bucket one-third full with compost. A five-gallon bucket available at big-box stores is ideal.

Step 2: Add water to the top of the bucket. An option at this point is to add an organic supplement to strengthen the compost tea. Janssen prefers unsulphured molasses at 1/2 ounce per gallon (the sugar wakes up the bacteria). Unsulphured molasses is available at most grocery stores. Other supplement options include organic fertilizers such as fish emulsion or powdered seaweed. Follow directions on the package to add these.

Step 3: Let the mixture steep for up to four days, stirring it occasionally.

Step 4: Strain the mixture through a porous fabric into another bucket. Spread the leftover compost on your garden or put it back into the compost bin.

Step 5: Dilute the liquid from the compost with water at a 10:1 ratio. It should have the color of weak tea.

Step 6: Use the tea immediately as a soil drench or as a foliar spray applied with a standard garden sprayer. When using as a foliar spray, add a small amount of vegetable oil or mild dishwashing liquid (a rate of about one-eighth teaspoon per gallon is sufficient) to the mixture to help it adhere to the leaves.

Helpful hints

  • The compost: It should be well-finished. What does that mean? It should have the crumbly texture of cornmeal and smell earthy, like the woods when you go for a hike. If you are not sure whether your compost fits this description, dig to the bottom of the compost pile or bin. That’s where the “good stuff” will be.
  • Brewing time: A good rule of thumb is 24 to 48 hours.
  • Aerating the mixture: You might see some "recipes" that call for using an aquarium pump, an augur or another device that runs continuously during the brewing process. That is not necessary for this simple bucket-brewing method. All you have to do is stir the tea a few times during the days it is brewing.
  • Adding supplements: As mentioned above, the sugar in unsulphured molasses will wake up beneficial bacteria. Other organic supplements of your choice can also be added.