When should I plant sweet pea seeds?

There’s more than one good time to sow sweet peas for summer fragrance.

Battling unseasonal weather can leave you feeling like throwing your usual gardening schedule out of the window. 

Extreme rainfall is becoming more frequent in the UK, according to the Met Office. And many of us have been left finding ways to protect plants from a late frost, just when we thought it was safe to start celebrating spring.

Red and pink sweet peas growing in a gardenCredit: Shutterstock / Moravska
Annual sweet pea plants need sowing each year

Unpredictable weather can leave those planning a cottage-style garden for summer wondering, ‘When should I plant sweet pea seeds?’. 

If you love the sight and smell of fragrant sweet peas delicately weaving themselves around wigwams, then you’re in luck. That’s because there are two windows each year – one in spring and one in autumn – when you can start sowing sweet peas. 

When should I plant sweet pea seeds?

You have two opportunities to sow

Though the perceived planting window for sweet pea is wide (October-March), gardeners should avoid getting started in the darkest months of December and January due to the lack of light. That means there are essentially two smaller planting windows – October to November and February to March. 

Horticultural adviser and organic kitchen gardener Michael Thurlow told us sweet peas can be sown as early as February. And though we know spring is an ideal time for sowing sweet pea seeds, they can also be sown in October and November too, according to the RHS.

Though spring is an ideal time for sowing sweet pea seeds, they can also be sown in October and November

But does it matter what type of sweet pea you are sowing? Well, not really. Despite there being different types of sweet pea available (see below), the general consensus is that they can be sown at the same times of year. Guy Barter, chief horticulturist at RHS told us, however, that perennial varieties are often sown in April.

sweet pea seedlings growing in some cardboard toilet roll inner tubesCredit: Shutterstock / Ian Grainger
Loo roll inner tubes give sweet pea’s long, narrow roots rooms to grow

Barter also explains that sweet pea seeds need warmth. If you’re sowing any sweet pea seeds in the autumn, they’ll only survive the cold winter and any frost if they have somewhere warm, bright and dry to grow until they’re ready to be planted outside in spring. This can be a heated propagator or a warm, bright windowsill with a radiator nearby. 

The upside of sowing sweet peas in autumn is that surviving plants will be much sturdier going into the ground when the time comes.

Are all sweet peas the same?

Two of a kind: annual and perennial

There are two distinct ‘types’ of sweet pea: an annual (lathyrus odoratus) that needs sowing from seed each year, and perennial lathyrus (such as lathyrus latifolius) that will keep growing back and appreciates a little maintenance to flourish. 

Their characteristics can vary, depending on the type you buy. Perennial lathyrus tend not to be fragrant (except Lord Anson’s blue pea) and have fewer colour choices than annual sweet peas. But as we’ve explained, they can be planted at the same times of year. 

Despite their edible-sounding name, did you know that sweet pea plants are toxic to cats, dogs and horses, as well as us humans?  

If you have furry friends or children and are propagating sweet peas indoors, make sure you place them well away from curious mouths and paws. The same goes for cut sweet pea flowers. 

Young Sweet Pea Plants Climbing up a Hazel Wigwam on an Allotment in a Vegetable gardenCredit: shutterstock / Peter Turner Photography
Sweet peas like to climb around a support

All sweet peas will prefer a sunny spot in your garden, like to climb around a support and grow best in peat-free compost that holds moisture, but still drains relatively well. This makes them a good option for growing in tubs and containers, but they can also flourish in raised beds and borders, too. 

Sweet pea seedlings have long, narrow roots that need room to stretch their legs properly. That’s why specially designed root trainers were made for them (check out this selection on Amazon). 

If you don’t want to buy a root trainer or would prefer to reuse something from around the house, then head to your recycling bin. The cardboard from a loo roll can be just as effective (or from a kitchen roll, cut in half). Plastic trays with holes that hold your strawberries and grapes will also do the trick, as will a clean food tin, as long as you’ve drilled drainage holes into the bottom.  

How easy is it for sweet pea seeds to germinate?

There’s a tough seed coat to crack

Knowing when to plant sweet pea seeds is one thing. Ensuring their successful germination is another. 

Sweet peas, like many leguminous (pea family) plants, have a very tough seed coat. This means it can take a while for water to penetrate the seeds after sowing, leading to slow germination and losses due to rot, Barter told us. 

Close up of a sweet pea sprout. Young seedlings in tray on window sill pea seedling in greenhouseCredit: Shutterstock / Anna Lovnik
Some people soak sweet pea seeds overnight to ensure successful germination

Some techniques to avoid this include people scraping seeds with sandpaper or chipping the seeds with a knife. Others soak the seeds overnight. Some place the seeds in a heat-proof container, cover them with boiled water from a kettle and leave them to cool.  

“I prefer to put the seeds in an airtight plastic box on some wet kitchen towel and leave in a warm place”

“I prefer to put the seeds in an airtight plastic box on some wet kitchen towel and leave in a warm place, such as the airing cupboard, and when they sprout (chit), I plant them into pots of peat-free potting compost,” says Barter. 

“Having said that, I know of many people who simply sow sweet pea seeds in the soil and get good results. The truth is, I suppose that seed lots vary with cultivar and length of storage.” 

Purple, pink and red Sweet pea flowers growing in a garden in british summer timeCredit: Shutterstock / Adriangeorge
Stagger planting from late spring to early summer for a longer flowering season

When should sweet peas be planted out?

Avoid combinations of rain and frost

Thurlow advises that the best time to plant your sweet pea seedlings is April or May, though this is frost dependent.

According to Sam Gallivan, team leader at RHS Wisley’s nursery and propagation unit: “Sweet peas are exceedingly tough. They will survive outside in frosts with absolutely no problems whatsoever.” But a sweet pea plant’s nemesis is a combination of both frost and rain together, so they shouldn’t be planted into the ground if this is still a risk. You could, however, keep them under a cold frame.  

Sam recommends staggered planting from late spring through to early summer for a longer flowering season. 

Ready to get going? Check out these sweet pea seeds, with prices for a packet starting from £2.

Rosanna Spence

Written by Rosanna Spence she/her

Updated:

Rosanna Spence has been a journalist for nearly 10 years, reporting on a huge array of topics – from microwaves to cocktails, sustainable buildings, the Caribbean islands and beyond. She’s interviewed chefs at the helm of Michelin-starred restaurants and chatted to countless CEOs about their businesses, as well as created travel guides for experienced travellers seeking life-changing adventures. Throughout her career, she has created content for Business Traveller, i-escape.com, Pub & Bar, BRITA, Dine Out and many more leading titles and brands.

  • linkedin