You already compost—you do compost, don’t you?—use compost in your garden and container plants, and understand all of the soil-building benefits that compost provides. Now it’s time to familiarize yourself with compost tea, an easy-to-make brew using black gold. It’s too easy, in fact, to not take full advantage of it.
This is the key difference between compost and compost tea: Both are chock-full of nutrients for your soil, but the nutrients in the tea are already in solution, available to be used immediately by your soil microorganisms and plants. The nutrients in the compost will feed those microorganisms and build your soil’s organic matter, boosting plant and soil health in the long-term, but they are not in a form that can be used right away. According to Guy K. Ames, horticulturist at the National Center for Appropriate Technology, compost tea is an effective—and cheap!—quick-release fertilizer.
So Long Sick Plants
There’s a lot of chatter about the disease-suppression properties of compost tea applied to plants’ leaves, but Ames doesn’t buy it. “It’s not based on a whole lot of research,” he says. In fact, some research points to the idea that compost tea can actually promote diseases, such as brown rot in sweet cherries. Ames, a longtime fruit grower, recalls one study that shows compost tea suppresses apple scab but says no one has been able to replicate the results since.
The very nature of compost tea, however, will boost the health of plants, particularly if you are applying the nutrients directly to the roots rather than as a foliar spray. It stands to reason that plants that are healthy to begin with are better equipped to fight off diseases.
If you’ve ever made a cup of tea, you pretty much get the process of making compost tea.
“You’re taking finished compost and soaking it,” Ames explains. It can be as simple as that, if you want to make anaerobic compost tea. If you’d like to make aerobic compost tea—compost tea infused with some oxygen—it’s not much more difficult. Either way, start with finished compost (not fresh manure) between 9 and 12 months old—no older. Put it in some kind of breathable-fabric sack, like cheese cloth, pantyhose or burlap.
Anaerobic compost tea is not aerated, so oxygen is not introduced to the solution. Just soak your compost-teabag in a bucket of potable water for five to eight days, according to the University of Vermont Extension.
If you were to use anaerobic compost tea on your garden, treat it as you would the application of manure—the compost-tea-making could promote the growth of human pathogens, like Salmonella. The USDA National Organic Program standards say manure should be applied to gardens at least 90 days before the harvest of edibles that do not touch the ground (such as blueberries, tomatoes or okra) and at least 120 days before the harvest of edibles that do touch the ground (think lettuce, root vegetables and squash of all kinds). And don’t spray compost tea on the fruiting parts of the plant.
Aerobic compost tea starts out the same way: Put your compost teabag in a bucket of potable water. The difference is you’ll use an aerator, such as a fish-tank bubbler, to run oxygen through the water for 24 to 48 hours. “I don’t think [you] need to be careful about the above-ground parts when using aerobic tea,” Ames says, though he points out vegetables and fruits should always be washed before eating.
You can find aerobic and anaerobic compost-tea kits for sale online and in garden-supply shops to make your own, as well as compost-tea starter to promote beneficial-bacteria growth in your tea, but you can do it yourself without these products for the same result.
Use your compost tea right away—within four to six hours, according to the Oregon State University Extension. The longer it sits, the fewer beneficial bacteria and fungi will survive to improve your soil.
- Foliar spray is best done first thing in the morning or right before sunset, just like when watering plants.
- Applied directly to the soil, OSU Extension recommends 2 cups of tea plus enough water to get the solution down to the roots—a 1-to-1 dilution of tea and water is acceptable.
Ames points out there is no standard for compost tea. If there were to be a standardized compost-tea product, claims of disease suppression or exact nutrient values could be confirmed. Part of the beauty of compost tea, however, is that you can make it with whatever rich, finished compost you have on hand, from your table-scrap-and-lawn-clipping backyard pile to fine vermicompost and everything in between.