How to grow Sweet Peas from seed in South Africa

Applies to: Bijou Mix, Cupid Mix, Mammoth Mix and Old Spice Mixed (Lathyrus odoratus).

Sweet peas are cool-season annual flowers, not edible peas. Do not eat the seeds or pods, and keep them away from children and pets. Grow in full sun during cool weather, with fertile free-draining soil and steady moisture.

Quick sowing guide

Choose the correct growth type

Dwarf and container Sweet Peas

Cupid Mix: a very dwarf, spreading plant, roughly 15–25 cm high, suited to pots, baskets and border fronts. It does not need a tall trellis.

Bijou Mix: a compact bushy type, approximately 45–60 cm high. Use short twiggy support if stems begin to lean.

Use a deep container with several drainage holes. Space plants 15–20 cm apart or allow roughly one plant per 20 cm of container width; do not overcrowd a shallow hanging basket.

Climbing and cut-flower Sweet Peas

Mammoth Mix: a tall early climber, approximately 1.5–1.8 m—not a 45–60 cm dwarf.

Old Spice Mixed: a fragrant climbing mixture, usually about 1.5–2 m.

Install trellis, netting or strong twiggy support before sowing or planting. Tie in young growth gently until tendrils hold. For garden branching, pinch the growing tip above two or three pairs of leaves when plants are about 10–15 cm tall.

Sowing and planting

1. Sow direct or use deep root-trainer cells. Cover by 10–15 mm and water thoroughly.
2. Keep cool and evenly moist, never waterlogged. Darkness around the buried seed and cool temperatures support reliable germination.
3. Soaking is not essential. Never soak treated seed; for untreated seed, lightly nicking the coat opposite the embryo may help a stubborn batch, but damaging the embryo causes rot.
4. Harden tray-grown plants and transplant before roots bind. Sweet peas tolerate cool conditions and light frost better than heat, but flowers and soft growth can be damaged by hard frost.

Ongoing care

• Enrich the bed with mature compost before sowing. Feed container plants lightly with a balanced flowering feed once growth is established.
• Water deeply and consistently. Dry roots shorten stems and promote powdery mildew; saturated soil causes root disease.
• Mulch the root zone once plants establish, especially in warm districts.
• Pick flowers every few days and remove every seedpod unless saving seed at the end of the season.
• Maintain airflow and avoid wet foliage overnight. Watch for aphids, thrips, slugs, snails, powdery mildew and virus symptoms.

When to sow in your region

Winter-rainfall Western Cape: Sow from late summer through autumn for winter-to-spring growth. Use deep, free-draining soil and protect seedlings from prolonged saturation and snails. In very wet sites, sow under cover and plant onto a raised bed.

Frost-prone interior: Autumn sowing can give the best spring flowers where plants receive frost cloth or a sheltered position, but hard freezes are risky. Otherwise sow in deep cells under protection in mid-to-late winter and plant out as severe frost eases. The crop must flower before early-summer heat.

Humid coast and KZN Midlands: Sow for the coolest months. On the coast, autumn into early winter is usually most suitable; maximise airflow and morning sun. In the Midlands, account for local frost pockets and protect autumn plants from hard frost.

Hot-dry or subtropical interior: Sow in autumn as nights cool and grow through the mildest months. Keep roots cool with mulch, irrigate deeply and use afternoon relief where heat reflects from walls. Late sowings often fail once hot weather arrives.

Flower and harvest outcome

For a garden display, deadhead before pods form. For the vase, cut in the cool of morning when the lowest flower is open and upper buds are showing colour; place stems in clean water immediately. Frequent cutting is the main way to prolong flowering.

Safety: Sweet Pea flowers, pods and seeds are ornamental and must not be eaten. Do not confuse them with edible garden peas or with edible Nasturtium flowers.