With their glossy fruits in an array of colours, shapes and sizes, sweet peppers are a vibrant and attractive crop. These tender plants are best grown in a greenhouse, as they need warm conditions, but can also be planted outdoors in a sheltered, sunny spot, in containers or in the ground.
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- Harden off before planting outside
Month by month
Sweet peppers are tender and need warmth and full sun, so are best grown under cover in the UK, in a greenhouse, polytunnel, conservatory or coldframe. They are only really successful outdoors in milder parts of the country, and benefit greatly from cloche or fleece protection. Wherever you’re ultimately going to grow them, they need to be sown in warmth indoors.
Sow seeds from mid-February to early March for plants that are to be grown under glass, and in late March or early April for growing outdoors.
Sow into small pots or seed trays filled with moist seed compost and cover with a thin layer of vermiculite. Most seeds will germinate, so only sow a few more than you need, in case of losses.
Place in a heated propagator at about 18–21°C (65–70°F), or on a warm windowsill and cover pots with a clear plastic bag or clear lid to keep the warmth and moisture in.
As soon as seedlings appear, take the pot out of the propagator or remove the plastic bag. Keep plants at 16–18ºC (60–64ºF) in good light and water regularly.
Transplant seedlings once they have two true leaves into their own 7.5–9cm (3–3.5in) pot, maintaining a high temperature to encourage growth.
If you don’t have time to grow peppers from seeds, or don’t have a suitably warm, bright place to raise good plants, then buy young plants from garden centres in late spring and early summer. Grafted plants can also be ordered online for delivery from mid-April onwards – these more vigorous plants are particularly useful where growing conditions are a little cool.
Sweet peppers grow best in a greenhouse, polytunnel or conservatory, but will also grow outdoors in a very warm, sheltered, sunny spot (at the base of a wall for instance), but may produce a smaller crop. Each plant needs a large container – 30cm (12in) or more – filled with good quality potting compost. They can also be planted in growing bags (two or three plants per bag) or in the ground.
Move young plants into their final container in late April if growing in a heated greenhouse, mid-May in an unheated greenhouse, or late May/June to grow outside. These plants are tender, so only take them outside once there is no danger of frost. Pepper plants must first be acclimatised to outdoors conditions, by hardening off for two to three weeks, before planting out.
Plants will tolerate a minimum night temperature of 12ºC (54ºF), but do best if the temperature never drop below 15ºC (59ºF).
Before planting in the ground, warm the soil with polythene or cloches for two weeks. Choose your warmest, sunniest spot. Peppers like fertile, well-drained but moisture-retentive soil that is slightly acid. So dig well-rotted manure – at a rate of 5.4kg (10lb) per square metre/yard – into the soil before planting, but avoid using fresh manure or large quantities, as this promotes leafy growth at the expense of fruit.
Watering and feeding
Water little and often to keep the soil or compost evenly moist. Don't let plants dry out or get waterlogged. Mulch the soil surface to help retain moisture.
Plants in containers need regular and generous watering, as the compost dries out rapidly. But never leave the pots standing in trays of water.
Keep humidity high in greenhouses by damping down twice a day during hot weather. Temperatures above 30ºC (86ºF) may reduce cropping, so keep greenhouses well ventilated.
To boost cropping, feed with a high-potassium liquid fertiliser weekly once flowering starts.
Pinching out and supporting plants
Pinch out the growing tip when plants are about 20cm (8in) tall, to encourage branching, which should lead to more fruit.
Side-shoots (the shoots forming between the main stem and leaves) can be further pinched back if you want even more but smaller fruits.
You may need to stake plants if they produce a heavy crop of large peppers.
In a greenhouse, sweet peppers can be harvested from mid-summer into autumn. Outdoors, they will start fruiting later, usually in August, and finish earlier, once temperatures start to drop in late summer or early autumn.
Pick as required when the fruits are swollen and glossy. Most peppers ripen from green to red, but other colours, including yellow, orange and purple, are available. Harvest at whichever colour and stage of maturity you prefer, but bear in mind that leaving peppers on the plant to ripen fully will hinder further fruit development.
Glasshouse red spider or two spotted mite
Leaves become mottled, pale and covered in webbing, on which the mites can be clearly seen; leaves also drop prematurely.
They thrive in hot, dry conditions, so mist plants regularly. Use biological control in the greenhouse.
Look for colonies of greenfly on the soft shoot tips of plants or on leaves. They suck sap and excrete sticky honeydew, encouraging the growth of black sooty moulds.
Use your finger and thumb to squash aphid colonies or use biological control in the greenhouse.
Blossom end rot
Dark blotches appear on the ends.
Water regularly and not sporadically and never allow the soil to dry out.
Small white flies suck sap and excrete sticky ‘honeydew’ over the plant, encouraging the growth of sooty mould.
Use biological control or sticky traps in the greenhouse.
Gregg Wallace tempts us with his grilled vegetable terrine.
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