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How to Grow Sweet peppers RHS GYO Guide

By The RHS Advice Team

• Getting Started
• Choosing What To Grow
• Sowing
• Planting
• Plant Care
• Pruning And Training
• Harvesting
• Problem Solving

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Getting Started

Sweet peppers (Capsicum), also known as bell peppers or pointed peppers depending on the fruit shape, are tender plants that need lots of sun and consistent warmth to crop well. They are usually 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 or in long, hot summers, and benefit greatly from cloche A cloche is a  small, portable, protective structure made of glass or rigid transparent plastic used to protect plants, especially overwintered and early vegetables, from wet and cold weather and to warm the soil before planting. or fleece A soft, fibrous, translucent material laid over or around plants hastening their growth and protecting them against weather and pests. Heavier grades of fleece give about 2°C of protection from frost. It is usually used without supporting hoops. protection. Wherever you’re ultimately going to grow them, they need to be sown in warmth indoors, from late winter to early spring.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, usually reaching only about 60cm (2ft) tall and 30cm (1ft) wide, and grow well in large pots.

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Choosing What To Grow

There are many varieties of sweet pepper, with fruits of various shapes, sizes and colours, from wide and rounded to long and pointed, large or small, in shades of green, bright red, orange, yellow and purple. Long, pointed peppers are generally sweeter and have a thinner skin than rounded bell peppers.Some varieties are more suitable for outdoor cropping than others. Larger fruits take longer to grow and ripen, so if you’ll be planting outdoors, with a shorter growing season, it’s best to choose a variety with smaller fruits. You’ll also find several dwarf or compact varieties, ideal for containers on a sunny patio or balcony, or even a kitchen windowsill.

When choosing, look in particular for varieties with an RHS Award of Garden Merit (AGM), which should grow and crop reliably – see our list of AGM fruit and veg (135kB pdf) and our Recommended Varieties below. You’ll also find sweet peppers growing in the veg areas at the RHS gardens over the summer months, so do visit to compare varieties and pick up growing tips.

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. Grafted plants may also be available – these are more vigorous and should crop more reliably in cooler growing conditions. They can be ordered from online suppliers for delivery from mid-spring.

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Recommended Varieties

'Topepo Rosso' AGM

Italian heirloom variety with rounded, fleshy fruits, 8cm wide, crisp and sweet. Plants 60cm tall.

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'Redskin' AGM

Compact plants only 45cm tall, ideal for containers. Medium-sized fruits, from July.

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'Mohawk' AGM

Ideal for patio pots, this dwarf variety reaches 50cm tall, with bell-shaped fruits 10cm long.

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'Bianca' AGM

Mid-season variety with large fruits ripening from cream to yellow. Plant grows to 60cm tall.

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'Jolly Giallo'

Square-shaped, fleshy fruits, 12cm long, with mild, sweet flavour.

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'Corno di Toro Rosso' AGM

Large, tapering fruits up to 25cm long. Sweet flavour, crisp texture and thin skin.

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Sowing

Sow sweet pepper seeds indoors 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. To germinate, they need 18–21°C (65–70°F), so after sowing, place in a heated propagator A heated propagator is a portable heated structure with a vented lid and adjustable, constant, thermostatic temperature control. It provides a warm, humid environment to help seeds germinate and cuttings to root quickly. , if available, or on a warm windowsill. Once the seedlings A seedling is a young plant grown from seed. appear, keep at 16–18°C (60–64°F) in bright light and water to keep the compost Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. evenly moist. When seedlings have two true leaves, move them into their own 7.5–9cm (3–3.5in) pot, maintaining a high temperature to encourage good growth.For step-by-step sowing instructions, see our guides below.

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Planting

Young sweet pepper plants, either grown from seed or newly bought, must be kept indoors in the warmth, usually until at least late May. Then you can either plant them into their final container in a greenhouse or similar protected location, or get them ready for the great outdoors.Sweet peppers will grow and crop best in a greenhouse, polytunnel, conservatory or coldframe. In very warm, sheltered locations, you can plant them outside too, once overnight temperatures are reliably above 12°C (54°F). However, they are likely to produce fewer fruits outdoors, and the shorter growing season The period of time when an individual plant is in active growth. This will depend on the local climate and light levels, and can vary between different plants, although it is broadly from spring to autumn. means the fruits may struggle to ripen before temperatures start to drop in early autumn. Before planting outside, carefully harden off Gradually acclimatising tender or indoor-raised plants to outdoor conditions, to toughen them up and prevent a check in growth. Place plants outside in a sheltered spot during the day then bring indoors at night for a couple of weeks. Or place in a coldframe, opening the lid during the day. your plants for a couple of weeks, to acclimatise them to outdoor conditions. Give them your warmest, sunniest spot, ideally on a sunny patio or beside a south-facing wall, with temperatures of 15°C (59°F) or more. Plant them in their new location at the same level they were previously growing in their pot, and add canes to support taller varieties.Planting in containersPlant your young peppers into their final container in late April if growing in a heated greenhouse, mid-May in an unheated greenhouse, or late May/June if growing outside. Choose a container at least 30cm (1ft) wide and fill with peat-free multi-purpose compost Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. , planting one pepper in the centre. Alternatively, plant two or three in a standard growing bag. Add canes to keep the plants stable and upright.Planting in the groundChoose a spot with well-drained, fertile, moisture-retentive soil. If your soil is poor or very heavy, dig in a few bucketfuls of organic matter, such as garden compost or well-rotted manure, before planting. Alternatively, if you practise no-dig, mulch the soil ahead of planting directly into the mulch Mulch is a layer of material, at least 5cm (2in) thick, applied to the soil surface in late autumn to late winter (Nov-Feb). It is used to provide frost protection, improve plant growth by adding nutrients or increasing organic matter content, reducing water loss from the soil, for decorative purposes and suppressing weeds. Examples include well-rotted garden compost and manure, chipped bark, gravel, grit and slate chippings. . Warm the soil with cloches for a couple of weeks before planting so plants get off to a strong start. Space sweet pepper plants 38–45cm (15–18in) apart, depending on the variety. Compact varieties can be spaced 30cm (1ft) apart. Cover young plants with cloches to provide wind and cold protection, preferably until the end of June.

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Plant Care

Temperature and humidity

Sweet peppers can cope with a minimum night temperature of 12°C (54°F), but will grow better if kept above 15°C (59°F). However they don't like to be too hot – temperatures over 30°C (86°F) can reduce fruiting, so keep the greenhouse well-ventilated and put up shading in summer.Peppers also like high humidity The concentration of water vapour in the atmosphere. This affects the rate at which plants transpire (lose water from their leaf pores), which in turn affects how much water their roots absorb from the soil. If air humidity is low, plants transpire quickly and become at risk of wilting if water is lost from the leaves faster than it can be absorbed by the roots. Different plants require different levels of humidity to thrive. Many tropical houseplants need high humidity and are best grown in a steamy bathroom, misted regularly or placed on a saucer of damp pebbles. In a greenhouse, humidity can be raised in hot weather by damping down (wetting) the floor or overhead misting. , so add moisture to the air in warm weather by ‘ damping down In a greenhouse, damping down means wetting floors and other surfaces to lower the temperature and add humidity. This helps to prevent plants from suffering heat stress. ’ the greenhouse regularly – pour a full watering can over the floor, leaving it to evaporate during the heat of the day.

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Watering

Sweet peppers need a steady supply of water to grow and crop well, so water as needed, aiming to keep the soil or potting compost Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. evenly moist. Flower buds A bud is a small, undeveloped shoot that contains the potential for new growth. Buds are typically found on stems, where they can be apical (found at the tip) or axillary (found between leaf axils) and may develop into leaves, shoots or flowers. may fall off if plants get too dry. Plants in containers can dry out very quickly in summer, so check the compost regularly and be prepared to water daily in hot, dry weather.

If you are growing your pepper plants in the ground, mulch the soil with a thick layer of organic matter to help reduce moisture loss.

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Feeding

Feed pepper plants in containers with an organic, high potassium, liquid fertiliser weekly, as soon as flowering starts. Plants growing in enriched soil may not need regular feeding, but doing so can help to boost yield.

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Pruning And Training

Pinching out the growing tips of pepper plants is not usually needed to ensure a good crop, but can be done once plants reach around 30cm (1ft) tall to produce a bigger crop of smaller fruits. Be aware that pinching out can delay fruiting.Support each plant with a sturdy bamboo cane A cane is a slender, straight, length of woody plant material, usually bamboo. Canes are primarily used as plant supports. The fruiting stems of blackberries, raspberries and hybrid berries (such as loganberries and tayberries) are also known as canes, so these crops are often referred to as cane fruit. , tying in the main stem as it grows. If plants produce a heavy crop of large peppers, more support may be needed as the stems can be quite brittle and snap easily. Insert bamboo canes around the plant and attach the fruit-laden side-shoots using soft twine Twine is a soft, fine loosely woven string treated with preservatives for outdoor use. Used for tying in climbers and other plants to supports. .

Harvesting

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 early autumn. Pick as required when the fruits are swollen and glossy. Most sweet peppers ripen from green to red, but some varieties turn yellow, orange or purple. The fruits get sweeter as they ripen. You can harvest your 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 plastic-free fleece A soft, fibrous, translucent material laid over or around plants hastening their growth and protecting them against weather and pests. Heavier grades of fleece give about 2°C of protection from frost. It is usually used without supporting hoops. or bring potted plants indoors, to help the remaining fruits ripen.

Problem Solving

Aphids are attracted to sweet pepper plants, so check shoot tips and under leaves regularly to prevent colonies getting established. Several other sap Sap is a fluid that circulates through a plant's vascular system, in a similar way to blood moving through our veins. Phloem sap carries the sugars produced in the leaves by photosynthesis down to roots and other storage organs, as well as carrying minerals and hormones. Xylem sap is watery and transports nutrients absorbed by the roots upwards to the rest of the plant. Some plants leak sap from wounds or pruning cuts, and this is known as bleeding. -sucking insects can be problematic too, especially in a greenhouse and in dry conditions.

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Common Problems

Blossom end rot

Dark blotches on the ends of aubergine, tomato and pepper are alarming, but do not mean the end of the crop. This is called blossom end rot and is cau...

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Aphids

Aphids are sap-sucking insects, they have many predators and are the basis for many food chains. The sap sucking can cause a lack of plant vigour, dis...

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Grey mould

Grey mould, caused by the fungus Botrytis cinerea, is a very common disease, causing a soft decay of plant tissues accompanied by a growth of fuzzy gr...

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Glasshouse red spider mite

Glasshouse red spider mite is a common sap-feeding mite that can cause mottled leaves and early leaf loss on a wide range of greenhouse and garden pla...

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Glasshouse whitefly

Glasshouse whitefly is a common sap-feeding insect, mainly of house-plants and greenhouse plants. They excrete a sticky substance (honeydew), which al...

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