There are many negatives to consider. Looking on the web, most websites
about compost tea are selling products or services & are riddled with
myths, exaggerations, & outright lies designed to sell, not to inform.
Anecdotes are used in place of evidence, & there are "it worked for me"
testimonies up the wazoo. What most gardeners know of compost teas they
learned at local nurseries invested in building a clientelle for a
high-profit-margin product (dirty water) the components of which the
nursery cannot actually predict or control, promoted as good for sundry
benefits that are not actually proven. Tjere are many things about Compost
Tea that are potentially very harmful but all the "customer" is told is
it's an organic miracle doing only good.

The majority of claims for Compost Tea have not been validated by any
scientific study. Some few values have been proven, but generally not in
exactly the same way as promoted by nurseries & vendors.

"Lessons" & "workshops" at nurseries are designed to sell you stuff. You
will not be taught very much that is certainly true, & you will not be
able to sort out what is factual or at least possible, from what is
completely fabricated & baseless.

Harmful side effects are possible with Compost Tea. The majority of
harmful side effects are circumvented by using topcoatings of compost &
avoiding compost tea.

If a gardener is ALREADY doing everything properly & has well-balanced
soils that result from proper organic gardening practices, then loading on
compost soups can actually harm plants by duplicating already completed
processes -- it can be like adding fertilizer on top of fertilizer until
plants are cared for to death.

Because vendors want to sell multiple products, they rarely give good
instructions about what Compost Tea applications replace. So the gardner
can be encouraged to just that sorry outcome of "loving your plants to
death."

Top coating mulches provide a healthful slow-release fertilizing & even
low-Nitrogen fertilizers feed the microorganisms (slowly) so that the
microorganisms will produce the required nitrogen. Topcoating composts
feed & encourage healthful microorganisms at exactly the rate the soil
requires & which the soil can sustain long-term. By contrast, dousing a
garden with mulch soups will transiently (potentially dangerously)
overfertilize & may backfire, causing a rapid decline in microorganism
health, injuring plants, & inviting pathogenic microorganisms.

Bacteria (even healthful bacteria) produce waste products toxic to
themselves, including waste products beneficial to plants which by taking
in the nutrients keep the soil balanced for the continued health of the
microorganisms. When concentrated in liquid, this is a little bit like
having a population of a thousand mice in a cage big enough for only a
couple mice. Here again, the attempt to suddenly expand the microorganism
population can have the opposite effect. Slowly (hence safely) restoring
soils that are damaged, or not over-treating soils that are already well
balanced, is not achievable with compost tea.

The science does not support the common claim that these teas function as
organic pesticides. Exaggerated claims to the contrary seem to be based on
the ability to drown aphids with compost tea -- which could be done as
readily with plain water. Compost tea does NOT function as an organic
pesticide & any vendor claiming it does is proving only their own
willingness to lie to you -- who knows about what all else.

A good healthy compost mulch includes essential organic matter for the
garden. Compost teas have very little organic matter hence meets fewer of
a garden's needs.

The microorganisms in organic teas are frequently NOT beneficial, or are
the same microorganisms already in the soil in sufficient quantity.

One of the hugest claims for compost tea is when it is used as a spray,
the healthful microorganisms out-compete pathogens on the surface of plant
leaves. To date, no science quite supports the claim that compost tea
cures or prevents pathogens in the garden. To quote Dr Chalker-Scott, a
horticulturlist at the University of Washington, "In the peer-reviewed
literature...field-tested compost tea reported no difference in disease
control between compost tea & water." In an update on new science, Dr.
Chalker-Scott found that the best "evidence" for pathogen suppression is
to be found only in articles that are not peer-reviewed & so not
creditable. There are, however, some few narrowly definable positive
effects from compost teas & pathogens but not as formulated by or for
gardeners. For instance, some wood barks contain chemical components that
retard human as well as plant diseases; a tea made of the right kind of
bark may have actual medicinal qualities. We can expect this kind of
finding to be misrepresented by vendors as proof that their teas cure or
prevent things that have never been cured or prevented by compost teas.

Further, because the microbes in compost teas are never isolated &
identified, even if one batch did manage to have some microbe in it that
competed with, say, apple scab, the next batch would not have the same
microbial content. This probably explains why one German study found
MARGINAL benifit for apple scab, & a better peer-reviewed study found
none.

Another fatuous & elaborate claim is that compost teas repair anaerobic
soils making them aerobic. Vendors like to toss in a few fancy words so
they sound scientific. The reality is that anaerobic soils are caused by
poor drainage or overwatering, or by compacted soils, or high clay
content. You could put compost teas on them till the cows come home & not
help one bit.

The only proven benefit of compost tea is rapid insertion of
microorganisms into soil, which may or may not be needed by the soil,
which may or may not survive in the soil whose overall conditions are not
likely to be altered by such rapid infusions. All other claims for compost
tea should be regarded as vendor mystifications as yet unproven. Some may
turn out to be true; most will be roundly disproven but the claims will
nevertheless be made by vendors whose only goal is to party ou from your
money.

While unneeded microorganisms may abound in the tea, microorganisms that
might actually have been needed might not be present at all. Indeed in all
likelihood the missing microorganisms will also likely be missing from the
compost usedto start the tea.

The actual chemical properties, pH levels, chemical & microorganism
components, in compost teas, changes dramatically from batch to batch. All
claims of specific values or predictable effects are false. All claims of
specific uses for one "variety" of compost tea vs another "variety" cannot
be substantiated by predictable properties of the teas. Often the
microorganisms will not actually be beneficial.

Compost tea even at its best is inferior to a quality composted mulch of
organic material, both as a fertilizer & for its capacity to sustain a
maximum population of healthful microorganisms.

Compost teas are more likely than compost mulchings to pollute groundwater.

Topcoatings of compost release nutrients that are entirely used in the
garden. Compost teas wash out of the garden & contribute to the
eutrophication of watersheds.

Beneficial microorganisms that live in the organic component (not the
liquid component) of composts are known to inhibit the splash, spread,
leaching, or dispersal of pathogenic microorganisms. Compost teas
FACILITATE this dispersal!

Gardens self-mulch with leaf fall. Horticultural station studies have
shown that gardens never fertilized at all maintain themselves by
self-mulching. Permitting fallen leaves to become leafmold in the garden
does vastly more for a garden than removing them. A garden can permanently
recycle its nutrients if not interferred with. Compost Teas are by
contrast temporary fixes, supposing they even fix anything.

Garden centers brewing teas in your behalf do not as a rule have water
tanks in which to age the water & permit the chlorines to evaporate out of
it before they start their tea batches. They are selling you dirty water
alleged to be chock-full of beneficial microorganisms that probably don't
exist when "brewed" in chlorinated water which kills microorganisms. If
you made it at home you could let the water sit a day or two before mixing
in some compost & starting your tea.

Vendors have learned that by promoting a mythology about compost tea, they
can profit from easily duped gardeners who want to be organic gardeners &
are by & large suckers waiting to be clipped. Generally the nursery owners
have first convinced themselves so that they can feel honest promoting
stuff that is a mix of unproven, disproven, harmful, no better, &
frequently worse than older established methods of properly dressing soils
with organic composts.

Claims of nematode content are nearly always false. As well, nematodes
have to be introduced to soils undver very specific conditions &
temperatures & times of year that have nothing to do with compost tea.

Compost tea vendors like to call themselves "brewers" which is further
mystification of a simple process over which they have inadequate controls
for predictable outcomes. They want you to think what they sell you is as
predictable as the flavor of your favorite brewed beer, when there is no
uniformity of product at any level beyond how much fits in a gallon milk
jug. It is part of the smoke & mirrors with the intent of befuddling you
into doing something you probably wouldn't do if you were permitted to
think too long & too clearly: Don't pay good money for dirty water or
"brewing" equipment when you already have everything you need to do it for
free at home, or which frankly shouldn't be done at all when mulching with
compost does everything compost teas does, but vastly more safely &
better.

-paghat the ratgirl

--
"Of what are you afraid, my child?" inquired the kindly teacher.
"Oh, sir! The flowers, they are wild," replied the timid creature.
-from Peter Newell's "Wild Flowers"
See the Garden of Paghat the Ratgirl: http://www.paghat.com/