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treated wood and coffee chaff

  • Subject: [cg] treated wood and coffee chaff
  • From: Don Boekelheide dboekelheide@yahoo.com
  • Date: Wed, 7 May 2003 07:03:00 -0700 (PDT)

Hi, all,

Better late than never on this post. I've been pretty
busy in the rain, including one stint unloading a
compost truck (our only chance for a month to get a
load, the man said...) that left me looking (and
feeling - but not smelling) something like a
chocolate-dipped frozen banana. Anyway, belatedly...

(I also have some very cool news from Organic
Gardening mag, which I'll send later today, inch'allah
(can I still say that in this country??? Wait, some
guy who looks a lot like Donald Rumsfeld just rang my

Re: CCA wood for trellises: I personally don't much
care for cca treated wood. A bigger risk, I believe,
than translocation of the arsenic into plants is the
direct movement from cca wood surfaces to little
fingers to little mouths (or, given that kids like to
chew on all kinds of things, directly into little
mouths). If you use cca wood, paint it with something
tough and safe. Also, it doesn't last forever, don't
kid yourself. The arsenic stops termites (for awhile),
but not decomposition, especially in moist soil (ie
the base of a garden trellis set in soil with cement
in the hole). So, be ready in a few years to look for
the toxic waste dump you'll have to send it to. Just
my opinion - lead may well be a worse problem in the
inner city and there are plenty of 'bigger' issues
than cca lumber out there. Some good folks use cca in
their gardens, feeling the benefits outweigh the
risks. Your group has to make the call. But I'd paint
it if you do use it - that's pretty cheap and easy to
do. Personally, I avoid the stuff.

Coffee chaff ('silverskin') has worked ok for me as a
mulch and compost ingredient, tho I like cocoa hulls
much better for aroma... Coffee chaff blows around
when dry and mats when wet, but, you know, it's mulch!
That's a good thing. I can't find much on coffee
chaff's pH, but I suspect it is either a bit acidic or
even neutral (5-7 pH). The chaff is the remains of a
thin protective membrane around each 'bean' that cooks
and flakes off during roasting. 

I noticed Ray Schutt's note that the chaff is a good
source of nitrogen. Are you sure about that, Ray (your
other info was excellent)? You might be right, but I
suspect the C:N ratio and N level (important for
composting) is probably more like straw (low N). I've
seen coffee chaff as 200-300:1 C:N on one composting
chart (without a citation, but that makes sense to me)
- in other words, it might not enrich your soil with
nitrogen and if you mix it directly with soil it might
'tie up' nitrogen temporarily. That's different from
coffee grounds, which have a fair amount of N
(typically about 2%, I believe) and are quite acidic.
So, imho, good uses for chaff are as mulch (maybe
mixed with other stuff to keep them from matting when
wet and blowing when dry, and not piled too deeply)
and in the compost and worm bins.

Recycling and resource conservation in our gardens are
great ideas. Make the most of what you got.

Don Boekelheide
Charlotte, NC

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