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

Lathyrus odoratus

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.

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