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COMPOST TEA REVEALED

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First Step, Identification

A few years ago I went to a nearby permaculture convergence. (Actually a “permaculture conference; those people have the best terms for what they do). I’ve grown plants in what I learned was a permie way for many decades, so I’ve been accused of being a permaculturalist. I was even invited to do a presentation and host a farmden tour for the convergence.

While there, I had the opportunity to attend a lecture by someone who has been billed as the diva of dirt, or, at least, of compost tea, specifically aerated compost tea (ACT), Dr. Elaine Ingham. You’ve never heard of ACT!? It became the hot, new thing years ago, perhaps still is, as an alleged cure for poor soil and plant pests. I’d been skeptical and thought that hearing and speaking to Dr. Ingham in person could entice me into the fold.Making compost tea

  Dr. Ingham showed myriad images of fungi, nematodes, and other creatures that you might find in compost piles and teas. We saw many “bad guys” that lurk in poorly aerated composts and teas. The “bad guys” are bad, she asserted, because they release toxins into the soil and puff away valuable nitrogen, sulfur, and phosphorus in various forms as gases.

  Dr. Ingham suggested monitoring our compost piles and tea happenings by purchasing a microscope and, with the help of her workshops, identifying resident microorganisms. Hmmm; interesting, but is it really necessary for a green thumb?

  While the panoply of microorganisms discussed was impressive, I contend that even a well-aerated compost pile or tea is bound to have some poorly aerated pockets. It’s not a “bad guys” vs. “good guys” situation, but a question of generally favoring an excess of “good guys.” Also, once compost is spread on the ground, the large surface area presented is going to tip the balance even more in favor of aerobic conditions.

To identify what organisms are in a compost pile, you have to get them out of the pile and onto a microscope slide. Easy. Just soak some compost in water and strain it. Or use a compost teabag. But wait! Is that really the spectrum of microorganisms that call that compost home? Not necessarily. What are staring up at you from that microscope slide are creatures that can be leached most readily into water. What you see also might depend on how long you steeped the teabag and who can squeeze out into the water through whatever size holes are offered by the strainer or the teabag.

Will Compost Microbes be Happy Far from their Compost Home? More fundamentally, I question basic assumptions underlying the use of compost tea. Even if you have beneficial organisms in hand (figuratively) and sprinkle them on the ground, they’re bound to expire unless the environment is suitable. Microorganisms in the tea might have enjoyed life within the dark, moist innards of a compost pile; the soil environment ain’t nothin’ like home for them.

Spraying ACT or any compost tea on plant leaves should likewise have little or no effect on plant diseases; again, conditions on a leaf surface aren’t conducive to their survival. In the evolutionary scheme of things, why would a microorganism that thrives in the dark, moist, nutrient-rich innards of a compost pile survive on the sunny, dry, nutrient-poor surface of a plant leaf, let alone provide any benefits?Spraying plants

Over the last few decades, people have spritzed plants and sprinkled soils with compost tea, looking for effects such as improved soil structure or drainage or increased plant resistance to pests. Independent well-designed, vetted studies do not generally support claims made for compost tea.

True, there are some studies that show some benefits. I contend that if you spray just about anything on a plant leaf and have enough plants in the study along with sufficiently detailed measurements, some statistically significant effect might be noted. But every statistically significant effect isn’t also biologically significant. And looking over a number of studies, some few show a benefit from compost tea, many demonstrate no effect, and for a number of them, the effect of compost tea is detrimental.

Soluble nutrients do leach out of a compost teabag into water. The resulting compost tea, then, becomes a liquid feed for plants, effective either poured on the ground or even sprayed on leaves. So there can be some benefit from compost tea, a nutrient effect, not a microbial one.

Bulk is Good

Except in special situations, soil environments naturally host microorganisms that thrive best in them. A similar situation exists with earthworms. Years ago, perhaps still, advertisements in the back pages of gardening magazines would offer earthworms for sale. The reasoning went that good soils are teeming with earthworms, so purchasing and importing these creatures to you garden will make your soil better. Not true. The earthworms will die out if conditions and food are not to their liking. The same goes for microorganisms.

(An example of an exception to what I wrote in the previous paragraph is a study that was done in Puerto Rico back in 1950. THE USDA was trying, with little success to introduce a more useful, but non-native pine, to the island territory. Mycorrhizae are fungal symbionts that infect practically all plants; the fungus gets some foods manufactured by the plant in return for moving more nutrients and water to the plant for improved growth. The appropriate fungal symbiont was lacking in Puerto Rican soils. After inoculating plants with an appropriate fungus, the inoculated, introduced pines grew six times more than their introduced brethren that had not been inoculated.)Compost being shovelled

Except in rare situations, as in the example above, earthworms, microorganisms, and other creatures generally inhabit environments most congenial to their flourishing. Perhaps not enough of them, and what they really need is food to give their populations a boost, and food means some form of organic material. That is, bulky organic materials, such as compost, manure, leaves, and straw.

  Good gardening comes form using a pitchfork, not an elixir. Does anybody still make and use compost tea?

COMPOST TEA: SNAKE OIL OR ELIXIR? BLACK CURRANTS…

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Tea For Plants?

Has your garden had its tea this morning? Tea is all the rage for plants and soils these days. Compost tea. And not just any old compost tea, but tea you steep in water that’s aerated just like an aquarium.

Compost tea steeped the old way, by hanging a burlap sack of compost in a bucket of water for a few days, was one way to provide a liquid feed to plants. The liquid feed wasn’t particularly rich but did provide a wide range of nutrients that leached from the compost, and was convenient for feeding potted plants.COMPOST TEA MAKING

The new, aerated compost teas are billed as an efficient way to transfer beneficial microorganisms from compost into the soil or onto plant leaves. After all, spraying a little tea is less work than pitchforking tons of compost. In the soil, the little guys can spread their goodness, fighting off plant diseases and generally making plants healthier. Or so goes the logic and the promotional material.

Aerated compost tea (ACT) is big business these days, with people selling compost tea, compost tea brewers, and services for testing compost teas. Compost tea is more than big business; it’s bordering on religion (as anyone who criticizes compost tea soon finds out).

In fact, aerated compost tea is not the panacea it’s trumped up to be. Many independent studies have found the tea to be of no benefit, or even detrimental. Occasionally, human pathogens have been found lurking in compost tea.

In The Interest Of Science

I have a friend who believes in compost tea, so in the interest of science I agreed, on his urging, to try it out. To make sure any lack of efficacy could not be blamed on the tea itself, he sent me some compost, a brewer, and instructions for brewing and application. Interestingly, he told me not to try it out in my vegetable garden, because my garden was “too organic”(!)

Long story short: I applied tea to my lawn and to some vegetables in a relatively poor soil at a local farm, and the result was . . . (drum roll) . . . nothing, nada, rien, zip.

Tea Doesn’t Make Sense

All the buzz about compost tea bypasses the fundamental question of why compost tea would limit plant disease when sprayed on plant leaves? The theory goes that the good microorganisms colonize leaves to displace and/or fight off the bad guys.

Compost tea contains some of the microorganisms from the compost that made the tea. These microorganisms are normally found in soils and, of course, composts. But why, evolutionarily speaking, would these microorganisms provide any benefit on plant leaves, for disease control or any other purpose? Furthermore, these microorganisms evolved in a dark, nutrient and moisture rich environment. Why would they survive on a sunny, dry, nutrient poor leaf? The same goes for soils: If the soil has the right environment for a particular set of microorganisms, they generally are there; apply microorganisms to a soil lacking the needed environment and those microorganisms cannot survive.

Occasional research papers report positive effects of compost tea for thwarting plant diseases. I contend that if you spray just about anything on a plant leaf and measure enough plants closely enough, you’ll turn up some measurable response to the spray. That response might be very transitory and very small, but, with the right equipment or instrumentation, you’ll measure some effect. Whether that effect is of biological or practical significance is another story.

With that, I suggest someone begin a series of experiments to see the effect on plant diseases of spraying — say — milk solutions on plant leaves. Wait! A web search tells me that milk sprays have been tested and are, in fact, effective in controlling plant viruses, powdery mildew, and other diseases. In contrast to compost tea, which provides microorganisms but little of the food they need to survive, milk provides a smorgasbord of nutrients to whatever microorganisms tag along for the ride.

On the basis of the evidence, I’d go with milk rather than tea for my plants. And I’ll take my milk without tea.

Black Currants, Mmmmm

Moving on to something noncontroversial, my first black currants of the season ripened June 26th this year. Come to think of it, black currants may not be noncontroversial. Black currants have a strong, very

Belaruskaja black currants

Belaruskaja black currants

distinctive flavor, loved by some people, abhorred by others. The flavor starts out refreshingly tart as your teeth break the skin and then becomes sweeter and cooling, with a rich, resiny flavor, as you continue.

I count myself among the lovers of black currants, right up there

 with blueberries in my book. Black currants earned a whole chapter in my book, Uncommon Fruits for Every Garden. Although humans are divided on whether or not they enjoy fresh black currants, pretty much everyone loves the fruit concocted into jams and baked goods. They also flavor the liqueur cassis, I’ve used them to flavor beer.Black currant & Forget-me-not

Let’s be clear about the fruit in question. Black currants are not the same fruit as “dried currants.” Those currants are raisins made from dried Black Corinthe grapes, a name which was bastardized to “black currant.”

Black currants are borne on medium-sized bushes whose leaves, when brushed against, emit a strong, also resiny aroma. The leaves are sometimes brewed into tea — for humans, not plants.

COMPOST TEA: SNAKE OIL OR PLANT ELIXIR?

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Is the Jury Still Out on Compost Tea?

    In gardening, as in life, you can’t help but want to love some things, compost tea being one of them. After all, compost is good, tea is soothing, so what’s not to love about compost tea?
    Perhaps it depends on how you brew your tea. Traditional compost tea was and is made by hanging a burlap bag of compost in water, then diluting and drenching the ground or the potting mix of a potted plant with the nutritious, coffee-brown liquid.
    More recently, “aerated compost tea” (ACT) has soothed gardeners from coast to coast, the result mostly of the promotional efforts of soil scientist Dr. Elaine Ingham. This tea is brewed similarly to the traditional tea, except that extra foods, such as molasses (honey would seem more in keeping with the tea theme), brewers yeast, and bran, are also added, and — most important — the tea is aerated throughout the brewing process.

Brewing up a batch for some plants.

Brewing up a batch for some plants.

    The soothing effect from ACT is not nutritional, but biological. You spray the tea on leaves or soil to spread beneficial microorganisms leached from the compost whose populations were beefed up by all that aeration and added nutrients. These happy microbes fight off attack by pathogens and insects, perhaps by making the offenders sick or unable to reproduce, perhaps by making the plants more healthy, or any one of a number of other hypothesized manners.
    Coming from their home in the dark, moist, nutrient-rich innards of a compost pile, could these friendly microbes really be expected to survive on the bright, dry, nutrient-poor surface of a leaf? And evolutionarily-speaking, when would Mother Nature ever have made provisions for compost, let alone compost tea, let alone ACT microbes, to colonize a leaf and do good there? But this is all speculation; surely someone must have tested whether or not compost tea is really “soothing”  to plant life.

How to Really Test Effectiveness

    A slew of gardeners and farmers have tried ACT and can attest to its benefits. Matter of fact, a whole industry is dedicated to testing composts and compost teas, even selling compost tea brewers and compost tea itself.
    The way to truly ascertain the efficacy of compost tea is to subject it to the same scientific scrutiny as you would anything else: Come up with a hypothesis (such as “Compost tea prevents powdery mildew of squash plants”) and then design an experiment to test the hypothesis. Said experiment would need both treated (compost tea sprayed) and control (water sprayed) plants. Most gardeners and farmers go to the trouble of spraying compost tea because they believe it will be effective, so are not willing to leave a portion of untreated (control) plants. Their endorsements, then, must be taken with a grain of salt, and the same must be said for endorsements from anyone reaping financial gain from compost tea.
    One treated and one control plant, even one treated and one control plot of plants, would not be sufficient for a good test. Biological systems are complex. Grow 10 tomato plants under exactly the same conditions and some will grow a little more, some a little less than the others. With too few test plants, natural variations in plant growth might overwhelm variation due to a treatment. With enough plants to even out and offer a measure of natural variations in, say, plant growth, effects of a treatment are better parsed out.
    And finally, randomization is needed to even out any effects of, say, location. Perhaps one side of a plot is more windy, or the soil is slightly different, or there’s a bit more sunlight. Rather than have all the treated plants cozied together growing better or worse because of this added effect, even out these effects by randomizing the location of treated and control plants.
    Now you’ve got an experiment. Using a few arithmetic formulas or, these days, a computer program, you plug in the numbers and come up with a probability of an effect of the treatment. In agriculture, a 90% or 95% probability is usually considered sufficient. You can then answer “yea” or “nay” to the hypothesized question, in this example, “Does compost tea prevent powdery mildew of squash plants?” with a 90% or 95% confidence level

Okay, I’ll Try It

    I have a friend who is a big proponent of compost tea. Finally, he convinced me to give it a try but only after I made him agree to supply me with a brewer, some compost, and explicit instructions, just to avoid his finding excuses for failure of the tea treatment.
    A red flag went up when he advised me not to use it in my vegetable garden because it was “too organic.” I ended up, on his suggestion, spraying a few strips down my lawn and parts of some bean rows on a friend’s farms.
    This admittedly nonscientific test conclusively showed no benefit at all from the tea.

Snake Oil, Mostly

    So what’s the scientific verdict on compost tea? The answer is not so simple, in part because it depends whether the reference is to traditional compost tea or ACT, the kind of plant, the compost ingredients, how long the tea is brewed, how often tea is applied, etc.
 

Spreading compost, letting rain make the "tea."

Spreading compost, letting rain make the “tea.”

   Good experiments have been performed, from which the following general conclusions can be made: 1) ACT  is not reliably beneficial (and often has a negative effect or spreads human pathogens such as Salmonella); 2) Traditional compost tea has been shown to be often but only mildly beneficial for root diseases; 3) If sufficiently, but not too, dilute, either ACT or traditional compost tea can supply nutrients to feed plants.
    My pea plants succumb early every summer to some root disease, possibly fusarium. I am tempted to drench the soil for the peas with traditional compost tea. Perhaps I’ll even set it up as a crude experiment, keeping in the back of my mind the admonition of Charles Dudley Warner (My summer in A Garden, 1871), “I have seen gardens which were all experiment, given over to every new thing, and which produced little or nothing to the owners, except the pleasure of expectation.”
    Mostly, though, I’ll continue to do what I’ve been doing, spreading compost on top of the ground and letting rainwater make the tea.