Why I Sow My Sweet Peas in October: Stronger Plants, Earlier Blooms & Longer Flowering

Every autumn, as the days start to shorten, I make time to sow my sweet peas. Over the years, I’ve learned that October is the perfect month to start them. Sowing now gives my plants a real head start, leading to stronger roots, earlier blooms, and a longer display through summer.

Why I sow now for stronger, earlier plants

By sowing now, my plants have time to develop deep strong root systems over winter. When spring arrives, they’re already well-established and ready to surge into growth. I usually notice flowers by May.  

Fewer pests, fewer problems (depending on the weather)

One of the biggest bonuses of autumn sowing is that pests and diseases are minimised. Aphids and slugs are less active, which means my seedlings stay healthy and strong. Keeping them under cover, even outdoors protects them from becoming waterlogged or blown over. Plus, getting this job done in October lightens my workload in spring, when everything else in the garden seems to demand attention at once!

Better growth habits

Sweet peas are quite tough and cold-tolerant, so I can safely start them off under cover by the window in my shed. Either in a cold frame, unheated greenhouse, or even on a bright windowsill indoors would work too. They don’t grow much through the coldest months, just sit quietly through winter and burst into growth as the days lengthen.

Cooler temperatures and shorter days mean the seedlings grow stocky and sturdy rather than tall and leggy. That makes them much easier to manage when I come to plant them out in spring. When they have two or three pairs of true leaves, I pinch out the tips to encourage bushier growth and more flowering stems later.

Longer flowering season

I often do two sowings — one now in autumn, and another in February or March. The autumn batch gives me early flowers, and the spring batch extends the season well into summer for prolonged garden flowers and vases full indoors. In the spring I might sow direct rather than starting off in pots.

I like the reliable, old-fashioned varieties such as ‘Old Spice Cupani’, ‘Painted Lady’ and ‘Matucana’ as these have the stronger perfume though ‘Heaven Scent’ mix remains my favourite. The flowers are generally smaller but have interesting colour variations. Modern Grandiflora types share the scent of the older varieties but have bigger blooms. Spencer types are showier with big frilly blooms and multiple flowers per head. Typically not as scented.

My Simple October Sowing Routine

This is how I do it each autumn:

1. Use deep pots or root trainers (or cardboard centres of loo rolls) to allow room for long roots.
2. Sow 2 or 3 seeds about 2 cm deep per cell in a good-quality peat free seed compost. Note to self - don’t forget to label the pots!
3. Water lightly and cover with a thin layer of compost or vermiculite.
4. Keep in a bright, cool, frost-free spot (around 5–10°C). * TIP
5. Pinch out the tip of the main stems when plants reach 10–15 cm tall (do not thin out). This is to encourage development of side shoots.
6. Harden off gradually in March or April before planting out as a clump (do not separate).

* TIP. Passed on by Mo and Bryan Cliff to the gardening club. On a concrete or brick slab, light an 8 hour tea light and upend a terracotta pot over it. This compact ceramic heater will give sufficient heat to keep your greenhouse or cold frame frost free.

If you’ve ever wondered when to plant sweet peas for the best results, I believe autumn is the answer. A simple step that brings incredible rewards. By spring, I have strong, healthy plants ready to burst into colour, and I’m ahead of the game.

If you’ve never tried autumn sowing before, give it a go this year.  If all else fails, then you can re-sow in the spring!