Gardeners know compost is black gold, stay informed to
avoid risks
Dear Janet & Steven,
When I use the compost from my city I wonder about
chemicals in it. It is composed of lawn clippings, etc., that are
picked up for recycling from residents. Should I be concerned that
I do not know what went into this compost, as far as lawn chemicals
and fertilizer? I assume it is fine for the perennial beds, but
what about using it on a vegetable garden? Could this be a problem
if someone were to have overs prayed their lawn or is this such a
small chance that it is fine to use it? - J.C. -
Dear J.C.,
We use compost from yard waste facilities as we do any compost,
because it improves soil's nutrient- and water holding capacity,
reduces the need for fertilizer and suppresses disease. Researchers
have studied the risks as well as the benefits of using compost
with results so far that make us feel the benefits outweigh the
risks. You should decide for yourself. Here are some things to
consider.
There can be heavy metals in municipal compost from run-off on
streets where bulk leaves were picked up. There may be traces of
every chemical used by contributors of yard waste, from pesticides
to swimming pool treatments and cleaning agents. Yet my alternative
to compost may be to use soil stripped from building sites, which
may have its own contaminants.
Compost may contain pesticide residues. For instance,
researchers at Michigan State University studied three lawn
products through the composting process. They found that these
three, diazinon, 2,4-D, and pendimethalin (Prowl), changed form but
were still detectable. In those new forms in the end product,
however, they were so much less available to plants and animals as
to be no longer "bio-active."
A Rutgers University researcher analyzed compost from municipal
sites for traces of PCB's and 27 pesticides in the 1990's, and
found only chlordane. Chlordane was once widely used but was banned
in 1988. Some people may have applied this chemical after the ban,
but it's so persistent in the soil that it could have been old
residue in the tested compost. That Rutgers study concluded "no
risk" since plants do not take up chlordane from the soil.
A California Department of Health study added hazardous
chemicals such as carbofuran insecticide and simazine herbicide to
compost piles. After 50 days of composting, 100% of the
carbofuran and 98.6% of the simazine was degraded.
Recently there have been problems with plants being stunted or
killed by clopyralid residue in compost. Clopyralid, an active
ingredient in several agricultural and lawn herbicides, seems to
persist through composting. Although the product label states "Do
not use compost containing grass clippings from turf treated with
Confront in the growing season of application," that's pretty hard
to control unless it's your own home compost pile. So we're keeping
an eye on this issue. It was first identified as a problem in
Washington State, where the use of clopyralid has been banned as a
result.
Still, municipal composting has great advantages over most home
methods. Where yard waste arrives in huge amounts, it must be
composted quickly. So the process is handled scientifically, with
piles turned and mixed regularly to keep them as hot as they can
be. The end product is more likely to provide a benefit that
Cornell University has studied, the elimination of disease
organisms.
At Cornell it was determined that hot composting killed fungi
including gray mold (Botrytis), damping off
(Rhizoctonia), late blight (Phytophthora), white
rot (Sclerotinia), stem rot, bacterial blights, various nematodes,
wilt (Fusarium) and tobacco mosaic virus. This has
been verified by other studies such as at the National Arboretum.
The key is that composting must be done at 122 degrees and above.
That's hot composting, as done at large municipal sites and
regularly turned, well made home piles.
Perhaps you'll accept the risks in exchange for the luxury of
having compost in bulk. Then follow our lead in staying abreast and
using caution, too. We learn of new developments in compost testing
by reading news, magazine and Extension service reports. We discuss
it with others on this website. We wear gloves to handle compost,
since skin can absorb things that even a plant cannot.
Short reports
Avoid transplanting plants in active
growth.
We've transplanted at all times of year but know the
riskiest times are now when leaves are forming and in autumn when
they're falling. Give anything you move right now extra special
after care.
Green thumbs up
to pinching starting in May. If you want a mum, aster or other
plant to be bushier, clip its tips several times at three week
intervals before those shoots begin rapid upward expansion. Once
summer comes, pinching does little good.
Green thumbs down
to a gardener's fickleness. Several weeks ago we were in love
with our daffodils. Before that we couldn't get enough of the early
tulips and crocus. Now we find ourselves impatient for their
foliage to make way for the next round of color. Shame on us!
Originally published 5/1/04