Page 16 - ALG Issue 2 2025

VEGETABLES
NAS Blog – Growing Chilli Peppers
Growing your own chillies means you can enjoy a huge
array of colours, shapes, flavours and levels of heat – a much
wider range than you could ever buy in supermarkets. These
tender plants grow best in a greenhouse.
Chillies (Capsicum) are tender plants that
need heat, and lots of sunshine to fruit
well. Closely related to sweet peppers,
they make attractive plants with their
colourful, glossy fruits. They grow well in
containers and take up little space, with
compact varieties reaching only 20-30cm
(8-12in) tall. This makes it easy to grow
several different varieties, even when
space is tight. For the best crop, grow
them in a greenhouse, polytunnel or sunny
conservatory. They should also be happy
in a sheltered, sun-baked spot outdoors –
ideally beside a south-facing wall or on a
sunny patio or balcony. They generally like
similar growing conditions to tomatoes, so
are ideal companions.
There are hundreds of varieties of chillies
to choose from, offering fruits of various
colours, shapes and sizes, ranging from mild
to unbearably hot. Chilli heat is measured
in Scoville Heat Units (SHU), with milder
varieties such as ‘Anaheim’ rated at
500-2,500 SHU, ‘Jalapeno’ at 2,500-8,000
SHU, ‘Scotch Bonnet’ at 100,000-350,00
SHU and ‘Carolina Reaper’, one of the
world’s hottest chillies, at 2.2 million SHU!
Heat is not just dependent on the variety
though; it can also vary according to the
growing conditions and stage of ripeness.
Chilli seeds are available at garden
centres, online suppliers, and specialist
retailers offering a wide range of varieties.
If you’re short on time or space, you can
buy young plants in spring or early summer,
including grafted varieties that produce
larger crops. Some suppliers even offer chilli
plants in fruit during the summer months.
Sow seeds indoors from late winter to
mid-spring – chillies generally need a long
growing season, and an early start will give
you an earlier and longer harvest. Chilli
seeds need warmth to germinate – around
21°C (70°F) – so it’s best to use a
heated propagator, although a warm
windowsill should be fine too.
Once your seedlings appear, remove
them from the propagator and place
them in bright light at 16-18°C
(60-64°F), watering regularly. When they
reach 2-3cm (1in), transplant them into
individual modules or small pots with
multi-purpose compost. When the roots
begin to show through the drainage holes,
move them into larger 13cm (5in) pots.
Young chilli plants, whether grown from
seed or newly purchased, should stay indoors
in warmth until at least late May. Then, you
can either plant them in a greenhouse or
prepare them for life outdoors.
In mild climates, once night-time
temperatures are consistently above 12°C
(54°F) by late May or early June, you can
plant them outside. Be sure to harden them
off for 2-3 weeks to acclimatise. For the
best crop, choose the warmest, sunniest
spot, such as a sunny patio or south-facing
wall. Plant them at the same level as in their
pots and add canes for taller varieties.
To grow in containers, plant one in a
22cm (9in) pot filled with multi-purpose
compost, or plant three in a standard
growing bag.
To grow in the ground, choose a spot
with well-drained, fertile, moisture-retentive
soil that is ideally slightly acidic. To achieve
this, dig in moderate amounts of well-rotted
manure, at a rate of 5.4kg (10lb) per square
metre/yard, but avoid using fresh manure or
large quantities, as this can lead to lush, leafy
growth at the expense of fruit. Next, warm
the soil with cloches for a couple of weeks
before planting. Space chilli plants 38-45cm
(15-18in) apart, depending on the variety.
Dwarf varieties can be spaced 30cm (1ft)
apart. Then cover young plants with cloches
to provide wind protection, preferably until
the end of June.
Chilli plants can usually cope with a
minimum night temperature of 12°C (54°F)
but will grow better if kept above 15°C
(59°F). However, temperatures over 30°C
(86°F) can reduce fruiting, so in hot spells
keep the greenhouse well-ventilated and
put up shading.
Chillies thrive in a humid atmosphere,
so dampen the greenhouse floor daily
to increase moisture. Feed plants with a
high-potassium fertiliser weekly once they
start flowering. Harvesting typically begins
mid-summer in a greenhouse and by August
outdoors. To help fruits develop, bring plants
indoors towards the end of the season or
use grow lights to extend cropping.
Pick chillies while green to maximise your
crop, either for immediate use or to ripen
indoors. Leaving them on the plant to ripen
can reduce overall harvest by 25% or more
but results in a richer, hotter flavour and a
more decorative plant.
Whilst chilli plants are usually grown as
annuals, they are in fact perennial and can
be overwintered in a heated location, rather
than started afresh each year. This will give
you a head start on your chilli production
the following year. Plants should be pruned
back to a manageable size, then kept in
a warm, bright place, such as an indoor
windowsill or conservatory, and watered
sparingly.
David Allison
Horticultural Advisor at The National
Allotment Society
Chillies thrive in a humid atmosphere, so
dampen the greenhouse floor daily
16 | Issue 2 2025 | Allotment and Leisure Gardener