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Sweet peas (Lathyrus odoratus) are probably the most popular annual flower, being especially prized for their colour and scent. Smaller cultivars are available for hanging baskets and containers.
Common name Sweet peaBotanical name Lathyrus odoratusGroup Annual climber (also dwarf bush cultivars)Flowering time Late spring to summerHeight and spread 45cm-2.5m (18in-8ft) by 30cm (1ft)Aspect Full sun and well-drained but moisture retentive soilHardiness HardyDifficulty Easy
Sweet peas are easy to grow from seed, although you can buy plants in garden centres in spring. But there is a far wider range of colour and scent if you grow from seed.
In milder areas sow during October or November and overwinter the young plants in cold frames or unheated glasshouse. In colder areas sow seeds in late March or April.
Alternatively sow directly into the ground in March or April, but the results are generally less satisfactory.
Some cultivars have a hard seed coat and may be more difficult to germinate. Chip the hard seed coat opposite the 'eye' (small, round scar) using a sharp penknife to help moisture entry and germination. Don't soak the seeds as they are prone to rotting.
Grow sweet peas in fertile, well-drained, humus-rich soil and in full sun or very light dappled shade. For best results, incorporate organic matter such as garden compost or well-rotted manure at least four weeks before planting and apply a general fertiliser, such as Vitax Q4 or Growmore, at the manufacturers' recommended dose. After planting, water the plants well during dry spells.
Supports: Sweet peas are usually allowed to scramble up pea sticks, canes wigwams or trellis. Alternatively use post and netting supports. Use dwarf bush type sweet peas for pots, hanging baskets or as ground cover.
Pinching out: Remove the growing tips of autumn-sown seedlings when about 10cm (4in) high to encourage branching. It is not usually necessary to pinch out the growing tips of spring-sown seedlings although you can do if they get too long and leggy.
For a long and regular supply of blooms: cut flowers frequently, before they produce seed pods.
This method is used by professional growers to produce top quality blooms. Cordons are trained as single-stemmed plants to individual canes, with sideshoots and tendrils removed so that all the plant's energies are diverted into flower production. See the National Sweet Pea Society website for more information on this method.
There are many cultivars available, from high-quality exhibition blooms to those prized for their colour. Here are three that are particularly strongly scented:
Lathyrus odoratus ‘White Supreme’: White flowers, highly scented L. odoratus ‘Charlie's Angel’: Large clear pale blue flowers, scented, recommended for exhibitionL. odoratus ‘Gwendoline’: Large flowers with frosted pink effect, strongly scented
For more choices, check for RHS AGM Plants or use the RHS Find a Plant for over 50 cultivars with images and details.
Sweet peas can suffer from a wide range of problems, though few are very serious
Climbers and wall shrubs for sunClimbers: using annualsGrowing sweet peas with kidsNational Sweet Pea Society RHS The Garden article on sweet peasRHSTrials: Sweet pea trial results 2009RHSTrials: Sweet pea trial results 2010
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