Compost tea and seedlings. Image credit: sleepynecko, used under Creative Commons license.
When I posted a video on how to make compost extractions, and later on how to make compost tea it awakened my interest in this lesser-known subset of composting and organic gardening. I already knew that worm compost suppresses plant diseases, but could it be that making these magical potions from plain-old compost could enhance biological activity across your whole garden? It turns out there is an awful lot out there on the internet about compost tea—how to make it, what to make it with, how to use it, and whether it is any good at all. I thought I'd offer a primer on some of the better materials I came across. What Is Compost Tea?
The wikipedia entry on composting has a short but sweet overview of what compost tea is. Simply put, it's a liquid fertilizer and disease suppressor that is made by soaking small amounts of biologically-active compost in water, often with other ingredients such as kelp or molasses to feed the microorganisms, and then aerated over a period of one to two days. The "tea" is then sprayed using a typical hand-held sprayer either directly onto plants, the soil, or it is applied as a soil-drench (root dip) for seedlings.
A Simple DIY Compost Tea Recipe
Elaine Ingham over at FineGardening.com has an easy-to-follow recipe for brewing compost tea. Using no more equipment than a bucket, some tubing, an aquarium pump and bubblers, and a strainer, she explains how soaking and bubbling a mix of compost, molasses and water over a 3-day period produces a biologically rich feed that spreads the benefits of a small amount of compost over your whole garden.
Compost Tea Alternative Ingredients
Meanwhile this video from Howard Garrett, aka the Dirt Doctor, also gives a simple walk-through of how to make compost tea, and explains how adding different ingredients can help skew the biological activity. For example, says Garrett, adding molasses boosts bacteria—something that benefits grasses in particular. Meanwhile protein feeds like fish oil or liquid seaweed boost fungal activity, which is of more benefit to larger shrubs and trees.
Ready-to-Use Compost Tea Extractors
For those folks, like me, who aren't inclined toward MacGyver-like experimentation, it's worth noting that there are plenty of commercially-made compost tea making kits out there. Growing Solutions' compost tea making kits range from home- to farm-scale applications and boast something they refer to as "Fine bubble Diffusion Technology", as well as a proprietary compost tea catalyst. Meanwhile the makers of Keep It Simple compost tea brewers claim they have "the only lab tested, 12-hour brewing system in the world".
Image credit: Growing Solutions
Whether or not the claims being made by individual manufacturers amount to much is hard to say. But to an uneducated outsider, all of these kits seem to offer pretty much the same thing—a bucket, a pump, some form of aeration, and a system for extracting the fluid. That's not to say they aren't worth the investment—many of us would much rather buy a kit direct from someone who knows how to assemble it, than spend time rigging up our own version. But be wary of hyperbole and patented technologies. This isn't rocket science.
Commercially-Available Compost Teas
A quick search of the internet will reveal plenty of vendors selling compost teas for use in your home garden. Some, like Eco-Cycle from Boulder Colorado offer biologically active compost tea made from worm castings, and then sold fresh to consumers who are encouraged to use it the same day they buy it. Others are selling compost tea online, although it would be interesting to know how "bioactive" this stuff is once it's been sitting on a warehouse shelf for a few weeks.
How to Use Compost Tea
As for how to use compost tea, it's really not that complicated. As the Howard Garrett video above shows, it can be sprayed directly onto foliage, or soaked into the soil. It is also commonly used as a lawn spray, and is said to be highly beneficial for creating healthy turf. Eco-Cycle's product description includes a useful breakdown of how to use compost tea for different applications—including recommended frequency and whether or not to dilute the product.
Does Compost Tea Really Work?
Having known gardeners rave about the effects of compost tea, and being a firm believer that diverse, active, live soils are central to healthy plants, I admit that I am enamored by the idea of compost tea right now. After all, if compost is like probiotics for the soil, then compost tea should act like a super-food smoothie, right? But it is worth noting that not everybody is convinced. Lee Reich, writing over at FineGardening.com (yeah, the same people who offered that great how-to on making compost tea) warns that the jury is still out on compost tea. From suppressing diseases when used as a foliar spray, to improving biological activity in the soil, Reich claims that evidence of benefits is so far largely anecdotal.
Similarly, Linda Chalker-Scott, an extension horticulturalist and associate professor at Washington State University, has undertaken an extensive review of the scientific literature on compost tea—and turned up very little that proves the benefits of aerated compost teas. (Interestingly, non-aerated teas seemed to fair a little better.)
Whatever the truth about the science, there are plenty of people out there making and using compost tea. I would love to hear about readers' own experiences, tips, recipes, experiments or concerns. I know there are plenty of fellow compost geeks out there, so please feel free to share what you know.
More on Composting, Soil Life and Organic Gardening
How to Brew Compost Tea (Videos)
Compost is Like Yogurt for the Soil - Probiotics in the Garden
How Worm Compost Suppresses Plant Disease
Composting as Animal Husbandry
40 Tons of Life in One Acre of Soil (Video)