Garden News - July Digital Sampler

Why don’t my
Q growing bag
sweet peas flower?
Dennis Haynes,
Oxfordshire
Sweet peas
won’t flower
if their roots
are dry and
overheated
I wouldn’t grow
A sweet peas in
growing bags. Firstly, the
volume of compost is
very small and sweet
peas hate drying out. The
other reason is that in
front of a south-facing
wall, I suspect the roots
are getting poached in the
summer sun.
Sweet peas do best in deep,
well-cultivated soil, where their
roots are cool and moist. If
growing in containers, choose
ones about 45cm (18in) deep and
painted white to reflect the sun.
Alternatively, if the containers
are rectangular, line them with a
polystyrene sheet, which will
keep the roots cool.
Even with tomatoes that
tolerate warm roots, I prefer to
sink some bottomless 10 litre
pots into the growing bag and
plant into these so there’s a
larger volume of compost to hold
moisture and which is also less
likely to overheat.
What’s killing shrubs?
What are the growths
Q killing my shrubs?
Susan Greenwood, by email
The growths are lichens.
A They’re simply using the
shrubs as a support and take
all their sustenance from the
air. They do no harm to the
plants they grow on, but
where they become
established it’s a sign the
shrub is losing vigour.
Lichen can be controlled
to some extent by pruning
to improve air circulation
and additional feeding,
mulching and watering.
Always mulch and
prune shrubs well
Dennis Haynes
Alamy
Quick
Can you identify
the leaf problem
spreading through
my pear tree?
Baz Murray, by email
The blackening of the
leaves is due to the pear
blister mite (Eriophyes pyri),
a microscopic gall mite
that feeds inside the leaf.
Raised blotches start off
pink or yellowish-green,
but later turn black. It
doesn’t affect cropping
or the health of the tree,
which is just as well, as
there are no effective
insecticides against mites.
If just odd shoots are
affected prune them out.
How do I propagate my
dendrobium orchid from
the small plantlets on
the stems?
Margaret Hamilton,
by email
Under low-light levels,
dendrobiums produce
new plantlets, known as
‘keikis’, on the main stems.
Once three or four roots
form, sever the stem 2.5cm
(1in) above and below the
plantlet and pot into an
orchid compost. Keep well
watered, but out of direct
sun until established.
Questions
Pear blister mite
won’t harm your tree
Is it OK to treat blue
mould on my lifted
bulbs with sulphur?
Martin Hewitson, by email
Sulphur no longer has
approval for use as a
fungicide. Ensure your lifted
bulbs are thoroughly dried
off before storing them.
Remove any damaged bulbs
and any displaying obvious
symptoms. Store in trays
in a warm, airy location
until you replant.
Can I save my pieris?
Michael Wilson,
Keighley, W Yorkshire
Pieris are more droughttolerant
than other
ericaceous plants, but you
need to increase watering
to at least twice a week in
summer. They’re prone to
pieris lacebug attack, which
bleaches the foliage, but
this is associated with lots of
debris and stickiness on the
underside of leaves.
Baz Murray
Why are my plum
Q leaves curling?
Donald Parkes, West Midlands
The damage is due to the
A plum leaf-curling aphid
(Brachycaudus helichrysi), a sapsucking
insect that feeds on the
foliage of many prunus species.
It’s active from April through
to late May and will have left
trees by now. You can simply
prune back badly distorted
shoots.
To avoid it next year,
use a winter wash or
approved insecticide
for fruit as the leaf
buds are opening.
It’s worth examining
the underside of the other
leaves carefully, however,
as you may also see whitishgreen
insects which are mealy
plum aphid (Hyalopterus pruni).
These are active right into
late summer, when dense
colonies may develop, so a
timely spray may help. Never
spray any fruit tree when in
flower due to the danger to
beneficial pollinating insects.
Damage to plum
caused by leafcurling
aphid
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July 1 2017 / Garden News 49