How to grow sweet peas and best varieties

The colourful blooms of sweet peas, held on long, straight stems, make perfect cut flowers. Plus, the more you pick them, the more buds form to make fresh flowers. Not all varieties have their famous scent so check out recommended varieties.

They’re easy to grow as well. Most are climbers, which can be trained up teepees of canes, but you can also buy dwarf varieties for pots and baskets. It's best to sow the seeds in October for planting the following spring, but you can also sow in spring. Sweet peas are annuals which are raised from seed to flower the same summer and then die. There is a perennial cousin called Lathyrus latifolius, which has pink or white flowers, but unfortunately it's not scented.

Which? Gardening magazine grew a range of popular varieties to see which would give us the best display.

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Key facts

• Plant type - Hardy annual climber 
• Position - In a sunny border climbing up a fence or obelisk 
• Soil - Any

How to grow sweet peas: month by month

Sowing sweet pea seeds

Sow seeds during October for the best results. Alternatively, wait until February/March. Use in rootrainers or deep pots using a Best Buy compost for sowing seeds. There's no need to pre-treat seeds. Keep them at 16-18°C and they should germinate in 7-14 days.

Mice eat sweet pea seeds, so cover the seed trays or pots with a propagator lid until they’ve germinated.

Best sweet pea varieties

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Full testing results for sweet peas

Sweet peas for scent

Grandiflora sweet peas

Sweet peas for pots

Spencer sweet peas

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How we test sweet peas

Which? Gardening magazine trialled a number of the different sweet pea varieties at our trial ground in North London. 

We sowed them in October and grew them in our coldframes through the winter until April, when we planted them outdoors. The varieties for pots were planted in pots and hanging baskets. 

The ordinary varieties were tied in and deadheaded weekly, and sprayed with insecticide to control aphids and prevent viruses spreading.

 Throughout summer we noted how strong the scent was, how much flower coverage the plants had and if any were affected by pests or diseases. We also assessed them for the length and thickness of their stems to see if any would be good for cut flowers.

Growing sweet peas

Types of sweet peas

They’re divided into two groups: grandiflora and Spencer types. For an expert, the distinction is in the ‘keel’ petals (the lowest two petals) – grandiflora types have a ‘clamped’ keel, while Spencer types don’t. For the rest of us, the difference is that Spencer types have big, frilly blooms and, despite their name, grandifloras have smaller flowers and stronger scents. 

Modern breeding has blurred these divisions, though. Nowadays, grandifloras are claimed to have both the big flowers and long stems we look for in cut flowers, as well as the profusion of flowers and strong scent we love in the garden.

When to pinch out sweet peas

Pinch out the growing tip of the plant when three or four pairs of leaves have formed. This helps to promote healthy, bushy growth

Overwintering sweet plants

Once germinated, move them to a cool, sheltered position such as a coldframe. Young sweet peas like growing in cool conditions but don’t tolerate being frosted. If it’s too warm, they can become weak. Cover with fleece during very cold weather.

Try the best frost protection covers

When to plant sweet peas

Plant them in March or early April against a support they can wrap their tendrils around, such as a teepee made of bamboo canes. Tie them in to their support initially as they get established.

Help your plants with a recommended soil improver

Growing sweet peas in a container

Seed breeders have produced dwarf varieties that don’t need training and trail over the edges of pots and baskets. See our Best Buy varieties for pots above. Plant out in April in pots orhanging baskets. Use a Best Buy compost for containers and mix in a Best Buy controlled-release feed.

Picking sweet peas 

Pick sweet peas regularly to encourage them to keep blooming. At the end of the season, leave some flowers to set seed so you can collect it for sowing in autumn.

Spencer varieties are the ideal type for cutting, as the stems are particularly long – sometimes more than 30cm – and the blooms are large and fragrant. The first couple of flushes of flowers on most sweet-pea varieties will have straight stems, but after this the climbing tendrils may entwine the flower stems, causing them to bend. Keen growers snip off these tendrils, remove sideshoots and tie the sweet peas to their support to get the best blooms and stems.

Common sweet pea growing problems

Flower buds falling off

Wet soils, warm days and cold nights can make plants drop their buds. It’s nothing to worry about and they’ll soon recover as the nights warm up.

Virus

Sweet pea plants with virus have several symptoms: leaves become mottled, growth becomes stunted and flowers are speckled with another colour.

The virus is spread by infected sap. This is usually spread by aphids feeding plant to plant, although it can also be spread on cutting tools, so clean them between plants.

Unfortunately, once a plant has virus it can't be cured. The best advice is to remove it before the infected sap can be spread to surrounding plants. Controlling aphids will help to avoid virus problems in the future.

Powdery mildew

In dry summers, powdery mildew can become a problem. Keep plants well watered but don’t wet the leaves. Spraying with a suitable fungicide can slow its spread.

Read more about how to treat powdery mildew on plants