30 January 2021 | New Scientist | 51The back pages
ANNIEOTZE
N/
GETTY^ I
MAGESClare Wilson is a reporter
at New Scientist and
writes about everything
life-science related.
Her favourite place is her
allotment @ClareWilsonMed
These articles are
posted each week at
newscientist.com/makerWhat you need
A compost bin
Kitchen waste
Plenty of waste
low in nitrogen,
such as cardboard
or sawdust
WE ALL like to get something for
nothing, and one way to do that
in gardening is to make your own
compost from kitchen and garden
waste. If all goes well, you end up
with an earthy, fine brown crumb
within a couple of years, which
adds nutrients and structure to
your soil. But get things wrong,
and it turns into a slimy, stinking
mess. So what are the dos and
don’ts of composting?
The process is all about
exploiting the animals and
microorganisms that break
down organic matter, recycling
nutrients through successive
plant generations. Storing it in
a pile or compost bin retains
more heat to speed things up.
For raw materials, think in
terms of greens and browns.
This relates not to colour, but to
the relative nitrogen and carbon
content of the materials. Green
waste is relatively richer in
nitrogen and comprises things
like grass clippings and fruit and
vegetable scraps. Too many greens
suppress the desired microbial
processes, releasing smelly
ammonia gas. Brown waste,
which is richer in carbon, includes
cardboard, sawdust and autumn
leaves. Aim to dilute nitrogenous
green waste with three-to-four
times as much brown material.
For those like me, who are
chiefly looking for ways to dispose
of food scraps, it can be hard to get
enough browns. I used to use all
my household cardboard waste,
but food packaging is often
covered with thin films or labels
and I got fed up picking bits ofGood compost is free nourishment for the garden. But it takes
science to stop it turning into a slimy mess, says Clare WilsonScience of gardening
Feed your garden for free
plastic out of my compost. Now
I stick to cardboard I’m sure is
uncontaminated, like the tubes in
toilet rolls, or shredded corrugated
cardboard boxes. Sawdust works
particularly well if you can lay
your hands on any.
You also need to manage the
oxygen and moisture levels of
your heap. The better you do
this, the faster it will make usable
compost. Improve aeration by
turning things over a few times
a year. I do this by lifting the
container off the heap and forking
the contents into another bin.
You may also need to water your
compost heap if it looks too dry.
But don’t let it get too waterlogged
or anaerobic decomposition will
leave the heap smelling like rotten
eggs. “Most composters learn
through a process of trial anderror,” says Danielle Purkiss
at University College London.
Purkiss is running an
experiment to see how long
“biodegradable” plastics rot
down in home compost heaps.
Paradoxically, these cause more of
a problem for expert composters’
heaps. The label “biodegradable”
is given if a substance rots in
12 months, but experienced
hands may achieve a faster
compost life cycle than this.
Although I’m not an expert,
I can vouch for how satisfying
it is when your hard work results
in a finished product you can use
on your garden. “It’s a kind of
alchemy,” says Purkiss. ❚Feedback
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