i think i had started to write this up,
but i don't find the draft. so...

first of all some background. the soil
i normally use for one garden is mostly
clay that i've been reconditioning over
the years by growing cosmos and then
burying the leftover dried stems and any
other remaining organic materials i can
find in a long trench. from year to year
i keep moving the trench back and forth
digging it up and chopping the stems as i
shovel. the stems don't fully rot for
several years.

this past year after reading about terra
preta and biochar i thought i would try to
make some charcoal and then use it in areas
to see what the effect would be on seed
sprouting (and later growth as the season
advances) for several species of plants.

first of all i used the worst part (the
area with the most clay) of the trench from
last season to dig down further into the
clay (about 3ft down total). making a
space about 10ft long and 3-4ft across. i
put all the super dry cosmo stems and other
easily burning stuff in the bottom and
stomped it down good before taking some
dried up shrubs and trimmed off all the
small leaves and stems and put that down
next with the trunks on top then stomped
all this down too.

then to start building a canopy i put
some long branches across and other longer
pieces of wood and old pallet pieces that
we would normally just bury and let the
fungi/mushrooms work on. on top of these
i put some cardboard and damp earth to
seal things up on top. i left both ends
open a little so i could get a fire going.

with the wind shifting constantly it
was a real PITA. i walked miles around
that trench and the smoke kept shifting to
follow me. with my lungs it wasn't the
best, but the smoke actually was mostly
steam coming out.

as the ends burned and dried the covering
soil it tended to cave in and self limit
the amount of oxygen, but i also wanted to
make sure it was getting hot enough to char
as much of the materials as possible.
using such a primitive thing as a trench,
cardboard and dirt i wasn't going to get
perfect results. i was curious to see
how well it would do anyways. a more
controlled setup like a double burner made
of metal would probably give better results
but that is beyond my current skills to
build/operate.

after several hours of steaming and
burning i finally buried the largest
chunks remaining and called it a day.
heavy rains that night and the next day
put the trench under water and i was
busy for a few days letting it dry out
a bit before curiousity and time became
available to do a little digging. after
a few minutes i could tell there was a
lot of change in how the clay and
charcoal with plenty of water added was
sticking to the shovel. actually, it
wasn't. that was an immediate nice thing
when it comes to clay. i normally spend
a fair amount of time just knocking or
scraping the stuff off the shovel. this
made digging it all up much easier and
faster.

i ended up with about 3cu feet of
charcoal and as i was digging it out
it mixed somewhat with the baked clay
and clay around it. there was standing
water at the bottom of the trench so
that gives you an idea of how wet it
was, but i didn't have much of a
sticking mess problem at all. for
that reason alone i would consider this
a good thing... what it will do longer
term we shall see, and if i keep making
more and adding it that will also be
interesting to see what happens.

with the charcoal/clay mix i made two
test areas a few feet long and a little
over a foot across separated by normal
soil of about the same size and another
part on the other side with some extra
sand in it. then i ran four lines of
different seeds through the whole area
crossing the test patches, regular soil
and added sand soil. after about a week
it appears to not have negatively impacted
seed germination for birdsfoot trefoil,
alfalfa, green beans or buckwheat. i
expected some change because it was so
newly burned and it wasn't mellowed at all
by adding any compost or aged or anything
other than watered.

further through the season i will keep
an eye on all of them and see how they do.

i'm unsure what i will do in the future
as the burning took a lot of effort. a
better means of doing it (covering with
metal instead of cardboard) and then sealing
it up with dirt would let me fire it, get
it going and then leave it alone so i wouldn't
have to spend so much time monitoring and
fiddling. of course an oven with temperature
and oxygen controls would be much better but
that's unlikely to happen any time soon here.

the carbon in the charcoal should stick
around for many years longer than the stems
and sticks otherwise would have so this is
a sure soil building tactic. adding compost
and green stuff to it and then getting some
worms planted into it would certainly make
it even better. the charcoal itself will
lighten the clay, i've already seen the
direct evidence in that from digging it out
of the trench.

grinding it up some would probably help too
as there are enough larger pieces in there,
but i'll let that go for now and let them
break down as i spade and turn under materials
as i normally would when done with a plot. the
stripes of birdsfoot trefoil and alfalfa along
the edge will be left alone for a multiyear
observation. other than weeded i have no
plans to turn or add materials to those
plantings other than what grows there itself.
unfortunately i didn't have enough material to
set aside larger areas to use as controls and
test plots or to have more variables to test.
some other time perhaps.

i thought for sure that the charcoal and clay
mix would be too harsh for worms but as i was
smoothing out the areas to get them ready for
seeding i did notice several worms in there
that seemed ok. it being so wet and the clay
probably well buffered or neutralized any harsh
chemicals. if it was dryer and there was dry
ash i wouldn't have expected to see worms that
is for sure.

so it is possible to make charcoal in a low
tech way and to sprout seeds in it within a
few days. nothing really earth shattering
in any of this, but interesting that the
effect on clay was immediate. i could see
why an ancient rain forest dweller with clay
subsoil (as is common in rain forests) would
notice it and want to use it for a garden/soil
ammendment.


songbird