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Notebook · Guide 1 October 2026 · Grow your own

Sowing sweet peas in autumn for earlier, stronger plants

Sow sweet peas in October or November, overwinter them in a cold frame, pinch them out and plant in April. Whether to soak or chip the seed, and how to stop leggy seedlings.

seasonalgrow your own
A row of deep root trainers filled with compost, each with a single sweet pea seed being pressed about 1cm deep.
1Sow one seed per deep root trainer, about 1cm deep.

You can sow sweet peas in spring, but autumn-sown plants get a head start: they build strong roots over winter and flower earlier next summer. The method is simple. The one thing to avoid is too much warmth, which gives tall, weak, leggy seedlings.

In pictures

  1. Sweet pea seedlings growing in a cold frame in winter, with the lid propped open for air.
    2Overwinter in a cold frame with the lid raised for air.
  2. Close-up of a sweet pea seedling about 7.5–10cm tall, with a dashed line marking where the tip is pinched out just above a healthy leaf.
    3At 7.5–10cm tall, pinch out the tip just above a leaf.
  3. Young sweet pea plants planted out in spring at the base of a wigwam of canes, spaced apart.
    4Plant out in April at the foot of the supports.

01At a glance

  • When: October to November (or late January to April for a spring sowing).
  • Where: a cold frame or unheated greenhouse over winter — no heat needed.
  • Plant out: April, after hardening off.

02Step by step

  1. Use deep pots. Sweet peas have long roots. Sow one seed per root trainer or 9cm pot, or five to seven seeds in a 13cm pot.
  2. Sow about 1cm deep in peat-free seed compost and water.
  3. Overwinter them cold. Keep them in a cold frame or unheated greenhouse. Leave the cold frame lid raised for air unless hard frost is forecast.
  4. Pinch out the tips when the seedlings are 7.5–10cm tall, just above a healthy leaf. This gives bushier plants with more flowering stems.
  5. Harden off and plant out in April, 20–30cm apart, at the base of supports.

03To soak or to chip?

You don't need to do either for most seed. The RHS's options:

  • Pre-swell: put seeds on damp kitchen paper in a sealed container somewhere warm, and sow as soon as they swell.
  • Chip only stubborn seeds that won't swell — nick a tiny piece of seed coat opposite the "eye".
  • Avoid soaking overnight unless you'll sow straight away; soaked seed can rot.

04Mistakes to avoid

  • Overwintering them warm. Leggy, weak seedlings.
  • Shutting the cold frame on every mild night.
  • Shallow pots. They need room for their roots.

05Safety

Sweet pea pods and seeds are not edible. Check our sweet pea profile for its safety flags, and keep seeds away from children and pets.

Save your money
No heat needed — a cold frame is enough.
Toilet-roll tubes or deep homemade paper pots work as root trainers.
Save your own seed from this summer's plants for next year.

How we checked this

Every care and safety claim on this page is verified against horticultural and veterinary sources.

Sources: RHS — How to grow sweet peas · RHS — Lathyrus odoratus

Checked 1 October 2026. If our advice ever conflicts with the RHS, believe them and tell us.