When should I sow sweet peas in the UK?

Two main windows. Autumn (October–November): the traditional approach, gives biggest plants and earliest flowers from May. Overwinter in a cold frame or sheltered cold greenhouse. Spring (January–March): start indoors at 10–15°C, transplant out from April. Spring sowings give a shorter season (June to August). Autumn-sown almost always crop better than spring-sown if you can manage the overwintering.

Do I need to soak sweet pea seed?

Yes — significantly speeds and improves germination. Soak in tepid water for 12–24 hours. Discard any seeds still floating after soaking (they're not viable). Some growers nick the seed coat with a sharp knife to speed soaking further; not essential.

Why aren't my sweet peas flowering much?

Most likely cause: not picking enough. Sweet peas stop flowering the instant seed pods form — the plant's whole purpose is to set seed, and once it has, it shuts down. Pick all flowers as they open, even if you give them away. Other causes: too much nitrogen (fresh manure pushes leaves not flowers — switch to high-potash feed); not enough sun; too late a sowing.

Spencer or grandiflora — what's the difference?

Spencer types: large modern blooms with frilly waved petals, long stems, the show-bench standard. Less fragrant than grandifloras. Grandiflora / old-fashioned: smaller blooms with plain petals, shorter stems, intensely fragrant. Cupani (the original, from 1699), Matucana (deep maroon-purple), Painted Lady (pink and white) are the classic grandifloras. Grow grandifloras for scent; Spencers for cutting.

How tall do sweet peas grow?

Standard varieties reach 1.8–2.4 m on supports. Dwarf cultivars (Bijou, Snoopea, Cupid) reach 45–60 cm and need no support — suit containers and edges. Cordon-trained sweet peas (single-stem, side-shoots removed) for showing can reach 2.5–3 m. Standard climbers are the most useful for gardens.

How do I store a glut of sweet pea seeds?

Save your own from grandiflora or open-pollinated cultivars (Spencer varieties are often F1 and don't come true). Let a few flowers go to seed at the end of the season; cut pods when they turn brown and brittle; pop the seeds out; dry on a tray for a week; store in a paper envelope in a cool dry place. Viable for 3–4 years. F1 hybrids must be re-bought each year.

Sweet pea — Grow

Sweet pea

Lathyrus odoratus

ornamental☀️ full-sun🪴 rich loam📏 climber🌡️ RHS H3–H4

☠️ Toxic to humans🐾 Toxic to pets

About

Sow sweet pea seed in October–November (autumn) for the biggest, earliest plants, or January–March (spring) for a shorter season. Sweet peas are hardy annuals (RHS H3–H4) — autumn-sown seedlings overwinter in a cold frame or sheltered cold greenhouse and produce far stronger plants than spring sowings. Soak seeds overnight before sowing to speed germination. Pinch out the growing tip at 4–6 leaves to force branching from the base. Climbing — build a wigwam, obelisk, or hazel pea-sticks 2 m tall. Plant out 20 cm apart after the last hard frost. Pick continuously from May–June — flowering stops the moment seed pods form. Spencer-type varieties for show; old-fashioned grandifloras (Cupani, Matucana) for fragrance.

Top tip

Sweet peas need rich soil, regular watering and support; pick flowers often to prevent seed setting.

Also known as: Ervilheira-de-cheiro, Lathyrus odoratus, Guisante de olor, Duftende Wicke, Sweet pea, Pois de senteur

How to grow sweet pea

1
Soak seed overnight
Soak sweet pea seed in tepid water for 12–24 hours before sowing. The hard seed coat softens and germination speeds from 2–3 weeks to about 1. Any seeds still floating after soaking should be discarded.
2
Sow in deep modules or pots
October–November for autumn sowing; January–March for spring sowing. Use deep root-trainers or 9 cm pots — sweet peas hate root disturbance and develop long tap-roots fast. Sow 2 seeds per cell, 2 cm deep, in peat-free multi-purpose compost.
3
Overwinter autumn sowings cool
Keep autumn-sown plants in an unheated cold frame, cold greenhouse, or against a sheltered north-facing wall. They want air, light, and protection from frost but NOT heat — warm conditions make them leggy. Pinch out the growing tip when seedlings have 4–6 true leaves.
4
Build the support before planting out
Wigwam of bamboo canes or hazel pea-sticks 2 m tall. An obelisk in a border. A length of netting on canes. Sweet peas climb 2 m and need substantial support from the start.
5
Plant out after the last hard frost
Late March in southern England (autumn-sown); mid-April for spring-sown. Space 20 cm apart around the support. Harden plants off for 7–10 days before planting if they've been under cover.
6
Pinch out, train, and tie in
If you didn't pinch the tip earlier, do it now. Tie new growth gently to the support with soft twine as the plants climb; they'll grip with tendrils but tying speeds them up.
7
Pick continuously
Cut flowers regularly — the more you pick, the more they flower. The instant seed pods start forming, flowering stops — so pick all flowers as they open, even if you don't have a use for them. A handful of stems in a small jug on a kitchen table fills the room with scent.
8
Feed weekly from flowering
A weak high-potash liquid feed weekly from the first flowers. Water deeply twice a week in dry weather. Sweet peas crop until late August in southern England; cut back hard once spent, and the plant may give a second flush.

Common questions

Safety Information

Humans

⚠ Moderate

Pets

⚠ Moderate

Always wash hands after handling. Keep away from children and pets if toxic.

Pest Resilience

2/5 — Somewhat vulnerable

Aphids, slugs, thrips, and pea moth can all be problematic; birds peck flowers.

The sweet pea year in your garden

Dispatching imaginary bots to check your garden out...

What to do now

How to Propagate

🌰Seed

Easy

Hardiness Zones

H1a (tender)H7 (very hardy)

H1a

H1b

H1c

RHS H3–H4

USDA 8 equivalent

Sweet pea

Sweet pea

About

How to grow sweet pea

Common questions

Safety Information

Pest Resilience

The sweet pea year in your garden

How to Propagate

Hardiness Zones

Names in Other Languages(4)