paghat wrote:

"Pam" wrote in message
...

Just make sure your compost is properly "cooked" - that will adequately
remove any lingering effects of pesticides

pam - gardengal

Some of the studies that show pesticide residues after hot composting to
be completely safe are not thinking organically, but are assuming safe
levels & degradation baselines that are tainted by the chemical
manufacturers' optimistic & propogandistic assertions about what
constitute safe levels. Deeper analyses disliked by the chemical companies
also show that even when a pesticide does degrade due to heat or passage
of time, new chemicals arise, some of which are themselves problems.

Plus, pesticides survive worm composts more or less intact. Had the pile
gotten hot enough for heat-tolerant microbes to break down pesticide
chemicals, the worms would be killed by the same process. Excellent
composts are made at lower temperatures by worms, but if pesticides go
into the process, pesticides come out of the process.

And that's without considering poor composting practices. I think most of
us from time to time jump the gun a bit & use some composts that could've
gone a while longer, or bury unfinished composts deep enough to finish off
right in the ground where new gardens are to be installed. These practices
are not generally harmful, but would more certainly mean the material
cycled back into the garden was never sufficiently hot to break down
unwanted chemicals.

There are a few pesticides & herbicides that survive even hot composts,
some banned (like chlordane) are insufficiently degraded even after many
years. Diazinon, atrazine, 2,4-D, & pendimethalin are among the
implicated. In big commercial or metropolitan composts they often use
microbial innoculants -- the same microbes used to help clean up oil
spills -- because normal composting would never rid the end-product of
pesticides where large amounts of contaminated grass clippings went into
the mix.

I wouldn't add anything to my composts I thought had been grown with
pesticides or herbicides, which pretty much rules out any grass clippings
from anywhere but my own yard.

-paghat

With the exception of your last statement, we'll have to agree to disagree.
The microbial activity of a properly managed compost pile is sufficient to
degrade to insignificant levels most commonly available residential pesticides
(with the exception of the two herbicides previously mentioned). Both diazinon
and 2,4-D have extremely short half-lives in the soil (7 days or less) and do
not require even an active composting process to breakdown, provided leaching
is not an issue.

Worm compost is another issue - it is not a true composting process (no heat
generation), but rather a digestive function of the worms, resulting in their
excrement being very high in plant nutrients. It is not recommended they be
fed much in the way of yard trimmings, anyway.

I also agree that home compost is often not mananged through a proper
composting process that develops temperatures hot enough to cook out pathogens
and pesticide residue, nor is it allowed the proper period of cooling that
encourages the populations of low temp microorganisms that complete the
composting process. Given these conditions, the only way one can be assured of
having truly "organic" compost is by confirming exactly what goes into the
finished product, however, local commercial composts meets certified organic
standards, for whatever that may be worth.

pam - gardengal
Certified Maser Composter