27 February 2021 | New Scientist | 49The back pages
FREDERIC^
HERBIGNIAUX/ALAMYClare 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
Copper tape
Pots
Nematodes
Garden cloches
OF ALL the gardener’s enemies,
slugs and snails are among the
most hated. Feasting on the soft
new growth of plants, they can
reduce prized blooms to rags
or demolish an entire row of
tender seedlings overnight.
They regularly top the list of pests
that are most enquired about
via the UK’s Royal Horticultural
Society (RHS) helpline, says RHS
entomologist Hayley Jones.
There are many possible
weapons against slugs and snails,
and they have different pros and
cons. I used to rely on slug pellets,
which leave satisfying numbers
of dead bodies, but can also poison
wildlife. The UK is set to ban
the most deadly kind, based on
metaldehyde, from March 2022.
Other slug pellets, like those that
contain ferric phosphate, are less
harmful, especially when scattered
thinly as per the instructions.
Research by Jones shows these
work nearly as well as metaldehyde.
Alternative tactics include covering
plants with cloches while they are
small and vulnerable, but these can
be pricey. A common DIY approach
is to surround them with sharp
material like grit or eggshells, but
Jones has found that this doesn’t
work – hardly surprising, as slugs
and snails can release thick mucus
to protect their undersides. They
can even crawl over razor blades.
Copper products like copper
adhesive tapes can also deter them,
although the reason why is unclear.
There is mixed evidence for copper,
perhaps because it is sometimes
laminated, but I have found that
putting copper tape around myFrom copper tape to tiny nematode worms, there are many ways
to deter slugs and snails. But which is best, asks Clare WilsonScience of gardening
Stop those slugs!
patio containers works well. It
is very satisfying to watch slugs
advancing up the pots, intent on
my sweet peas, only to be thwarted
by the tape. But make sure not to
let the protected plants be reached
via other overhanging leaves.
As well as using physical and
chemical weapons, you can go
biological by buying microscopic
worms called nematodes. Applied
as a fine powder added to water,
these worms seek out slugs and
kill them. These work well in trials,
but home gardeners report mixed
results, perhaps because they
aren’t following the instructions
exactly, says Jones. A common
mistake is to let the powder clump
at the bottom of a watering can
when sprinkling onto the soil.
Ideally, nematodes should be
applied every six weeks fromspring onwards. So in the
northern hemisphere, it is time
to order your worms by post.
I now have a dual strategy. For
my precious vegetable seedlings
at the allotment, I go all-out with
copper tape, cloches – home-made
from juice bottles – and the odd
slug pellet. But in the garden, I
have given up on plants that are
slug magnets, like dahlias and
hostas and stick to those that are
relatively resistant, but even these
may get somewhat munched.
Jones thinks the secret may
be to reach a truce. “You’re never
going to get to zero damage,” she
says. “The question is how much
can you turn a blind eye to?” ❚Feedback
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