Lathyrus odoratus, sweet pea

Sweet peas give a sensational show of exquisitely coloured flowers on floppy, scrambling stems that need supporting. The best have a rich scent that carries right across the garden.

Sweet peas arrived in Britain via a Sicilian monk who sent seeds to a Middlesex schoolmaster. This gave rise to countless other forms. The biggest relatively recent development came at the turn of the last century when unusually large, frilly flowers appeared suddenly in several parts of the country on 'Prima Donna'. Seed was saved and sold as new varieties.

'Countess Spencer', found in the garden of Earl Spencer at Althorp, Northamptonshire, was the best. It gave rise to the variably scented Spencer type which now has a huge range of varieties, with new ones being launched each year.

Recommended varieties

Unless growing the dwarf kind, you’ll need a bamboo wigwam around which to place the young plants. They can also be grown through shrubs or up supports for other climbers. A good show takes up quite a bit of space. You’ll also need to allow room to get close to keep deadheading, pick cut flowers and inhale the terrific scent.

L. odoratus 'Antique Fantasy Mixed': giving rich colours and strong scents, the plants have vigorous, strong stems and give a good summer show.
L. odoratus 'Matucana': one of the oldest and most beautiful sweet peas, it grows well above head height and has beautiful maroon and purple flowers with an exquisite scent.
L. odoratus 'Painted Lady': also reaching well over 2.1m (7ft), it has been very popular since the 18th century, and has bi-coloured pink flowers.

Dwarf varieties: For the gardener who doesn't want to bother with plant supports, there are a few dwarf varieties.

L. odoratus 'Bijou' : only grows to about 45cm (18in), and can be left to ramble along the ground. Other dwarf types, such as L. odoratus 'Snoopea', don't even form tendrils.
L. odoratus 'Little Sweetheart': an 18cm (7in) high sweet pea which is petite in every way. It comes in purple, red, rose, pink, blue, lilac and white. This variety is good for pots and at the front of a border.

Rediscoveries and new varieties: old kinds which were thought to have been lost crop up occasionally in people’s gardens, and are seized on by seed growers. But they're clearly outnumbered by the new kinds offering good vigour and a wide mix of colours.

L. odoratus 'Wiltshire Ripple': has marbled maroon and white blooms, and was recently rediscovered.
The Heavenly Group: a new range of striped flowers. For those who want lots of colour, look out for the Multiflora, Galaxy and Mammoth varieties.

Growing tips

Site and soil preferences

Sweet peas are hungry plants that love rich soil with plenty of added humus, and as much sun as they can get.

Pinching out

Encourage vigorous growth in sweetpea seedlings by pinching out the tops of the plants when they're a few inches high. This encourages lots of bushy side growth and more flowers.

Saving seed

Seed can be easily saved from the previous year's plants, although not all varieties reproduce exact replicas of the parent. Remove the seed pods from the plants and put them in a paper bag to dry out. Once they're dry, the pods can be popped open to release the seeds. If you plan to store the seeds, keep them in a cool, dry place.

Seed sowing

Plants are traditionally sown in pots in the autumn, as this produces sturdy specimens that'll be ready for planting out early next spring. They're quite hardy and can be safely grown in a cold frame. But they require occasional extra protection during periods of extreme cold and hard frosts. Or, in spring, sow seeds directly where you want them to grow.

To get a high germination rate, pre-germinate the seed on a sheet of damp kitchen paper. After a few days, the viable ones swell with water and a tiny root will appear. They can then be sown in pots of multi-purpose compost. The resulting seedlings should have their growing tips pinched out when they've produced two pairs of leaves, to encourage side shoots. This is important, because the original shoot will often fail to flower.

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Step-by-step growing guide

Place the seed on damp kitchen paper, in a tray covered with cling film. The seed will swell quickly and small roots appear.
Handling the seed gently and taking care not to touch the delicate root, sow them 1cm to 1.5cm (1/2in to 3/4in) deep and 3cm (1.5in) apart.
Grow the seedlings in a cool, light place. When they've grown two or three pairs of leaves, carefully pinch out the growing tip.
Gradually accustom the plants to outside conditions, before planting out from April. Water in and tie to the support.

Aftercare

Fork in a layer of moisture-retaining organic matter to improve the soil just before planting.

Problem solver

Mosaic virus

Aphids transmit this virus, causing the plants to grow poorly with speckled leaves and flowers. Pull out infected plants to help prevent the disease from spreading.

Bud drop

In periods of cold weather, the developing flower buds may turn yellow and fall off. Some varieties are more prone to this than others. It's usually only a temporary problem that's cured by the return of warmer weather.

Pollen beetles

Vast numbers of these small black insects can accumulate in the blooms, particularly with lighter coloured varieties. There's no chemical control available. The best advice is to place vases of affected flowers in a dark room with a light source at one end. The beetles will be attracted to the light, and should abandon the flowers.