With their colourful fruits, sweet peppers are a vibrant and attractive crop. These tender plants are best grown in a greenhouse, but can also be planted outdoors in a sheltered, sunny spot, in containers or in the ground.
Closely related to chillies, they make attractive plants with their colourful, glossy fruits, which ripen from mid-summer to early autumn. They also take up little space, reaching only about 60cm (2ft) tall and 30cm (1ft) wide, and grow well in large pots.
Month by Month
There are many varieties of sweet pepper, with fruits of various shapes, sizes and colours, from rounded bell peppers to long pointed peppers, large or small, in shades of bright red, green, orange, yellow and purple. The long, pointed fruits are generally sweeter and have a thinner skin than bell peppers.
Larger fruits take longer to grow and ripen, so if you’ll be planting them outdoors, with a shorter growing season, it’s best to choose a variety with smaller fruits. Some varieties are more suitable for outdoor cropping than others. You’ll also find several dwarf or compact varieties, ideal for containers on a sunny patio or balcony.
When choosing varieties, look in particular for those with an RHS Award of Garden Merit (AGM), which should grow and crop reliably – see our list of AGM fruit and veg.
What and where to buy
Sweet pepper seeds are widely available in garden centres and from online seed suppliers. Many also sell young plants in spring and early summer. These are ideal if you don’t have a suitably warm, bright place to raise good plants, or just want a few plants.
Grafted seedlings may also be available – these more vigorous plants should crop more reliably in cooler growing conditions. They can be ordered from online suppliers for delivery from mid-spring.
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 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 16–18°C (60–64°F) in bright light and water regularly.
Plant them 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. Containers should be at least 30cm (1ft) wide, or plant two or three in a standard growing bag. Add canes to keep them stable and upright.
Pepper plants will grow and crop best if kept in a greenhouse, polytunnel, conservatory or cold frame. However, in very warm, sheltered locations you can move them outside, once all danger of frost has passed (see Planting out, below). However, they are likely to produce fewer fruits outdoors, and the shorter growing season means the fruits may struggle to ripen before temperatures start to drop in late summer.
Keep pepper plants indoors until the night temperature is at least 12°C (54°F), usually by late May or early June. Then harden off for two to three weeks, to acclimatise them to outdoor conditions.
Sweet peppers need your warmest, sunniest spot to produce a crop outdoors, and do best if the temperature never drops below 15°C (59°F). They grow well in large containers, ideally on a sunny patio or by a south-facing wall, but can also be planted in the ground.
Peppers like fertile, well-drained but moisture-retentive soil that is slightly acid. So dig in well-rotted manure, at a rate of 5.4kg (10lb) per square metre/yard, before planting. Avoid using fresh manure or large quantities, which encourage leafy growth rather than fruit.
Also, warm the soil with polythene sheets or cloches for two weeks ahead of planting.
Space pepper plants 38–45cm (15–18in) apart, depending on the variety. Dwarf varieties can be spaced 30cm (1ft) apart. Cover with fleece or cloches initially, preferably until the end of June.
Temperature and humidity
Sweet peppers will tolerate a minimum night temperature of 12°C (54°F), but will grow better if kept above 15°C (59°F).
Temperatures over 30°C (86°F) can reduce fruiting, so keep greenhouses well ventilated and put up shading in summer.
Peppers also like a humidity, so during hot weather ‘damp down’ the greenhouse twice a day by pouring a full watering can over the floor, leaving it to evaporate.
Water regularly to keep the soil or compost evenly moist, ensuring plants neither dry out nor get waterlogged. Flower buds may be shed if plants run short of water.
Plants in containers may need watering daily in summer, as they dry out particularly fast.
Also apply mulch to help retain moisture.
See our guide to watering vegetables.
To encourage fruiting, feed pepper plants with a high-potassium liquid fertiliser weekly once flowering starts.
Pruning and Training
Pinch out the main growing tip when plants are about 30cm (1ft) tall, to encourage branching, which should lead to more fruit.
Side-shoots 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, as the stems are quite brittle and can easily break. Use several canes to support the branches, tying them in loosely.
Pick as required when the fruits are swollen and glossy. Most peppers ripen from green to red, but some varieties turn yellow, orange or purple. The fruits get sweeter as they ripen.
Pick the peppers at whichever colour and stage of maturity you prefer, but bear in mind that leaving fruits on the plant to ripen fully will hinder further fruit development.
Towards the end of the season, cover outdoor plants with fleece, or bring them indoors, to help the remaining fruits ripen.
Aphids are attracted to sweet pepper plants, so check shoot tips and under leaves regularly to prevent colonies getting established. Young pepper plants also need protection from slugs and snails.
In greenhouses, red spider mites and whitefly can be problematic, especially in dry conditions.
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