By Sarah Wilson
Learning how to grow sweet peas is really quite straightforward, but will reward you with some of the most exquisite summer blooms. It's no surprise that they regularly top the UK's 'favourite summer flower' polls, thanks to the variety of colours, incredible scent, and versatility.
What's more, they make wonderful cut flowers – simply arrange in a vintage jug or glass bottle to brighten your home. And the more you pick, the more they grow!
We've pulled together all the advice you need to get you ready to grow your own sweet peas this year. And once you're feeling inspired, why not head over to our guide on how to grow flowers from seeds too, for even more beautiful blooms?
When is the best time to sow sweet peas?
You can sow sweet peas in early spring, either into root trainers or, if the soil is warm enough, straight into the ground.
You can also sow your sweet peas in autumn, and then overwinter them in a greenhouse or cold frame which will protect them from the colder weather. The resulting plants often have stronger roots than those sown in spring and will flower earlier, too.
However, for the best of both worlds and a succession of blooms that will last right through the warmer months, you can sow some in autumn and a later batch in spring.
- Looking for more springtime inspiration? Head over to our spring garden ideas feature.
How to sow sweet peas in five simple steps
Step one: prepare your seeds
The experts at Floret suggest to soak your sweet pea seeds in water for 24 hours before sowing. This softens the seed coat, which in turn, speeds up the sprouting process.
Alternatively, Sue Sanderson from Thompson & Morgan says you can leave the seeds on moist kitchen roll until they swell or sprout. Lay the kitchen roll in a sealed container and place it in a warm room, she adds.
You can also weaken the shell slightly using a nail file, although this is a little more time consuming. If you don't have time to do any of the above, don't worry, your seeds should still germinate successfully, they just might take a little longer to do so.
Step two: sow the seeds into root trainers
Sweet peas have deep roots, so sow them in root trainers. These are deep modules that open out, so seedlings can be planted without their roots being disturbed. Fill them with a mixture of seed and multi-purpose compost, and, as Floret says, allocate two seeds per pot, using your finger to poke them a half-inch into the soil.
Alternatively, you can use cardboard tubes from toilet and kitchen rolls if you're after some budget garden ideas. These are ideal for sweet peas as they can be planted whole and will slowly decompose in the soil over time.
Step three: cover the seeds to speed up germination
Covering pots with a plastic dome lid will increase humidity and speed up germination, says the team at Floret. Place in a cool greenhouse, or in a bright window of your home.
Pop autumn-sown seeds in a well-ventilated greenhouse or cold frame, ready to be planted out next spring, once the soil has started to warm up.
- Our greenhouse ideas has tons of stunning designs to get you inspired.
Step four: pinch out the tips
Pinching out the tip of sweet pea seedlings as they grow encourages them to develop bushy side shoots that will produce more flowers.
The team at Floret says to do this when the plants are between 4-6 inches tall. Pinch just above a leaf joint, leaving two or three leaf nodes.
Step five: plant out your seedlings
When your seedlings are looking sturdy and the ground is warm outdoors, it's time to get planting. Before you do so, remember that sweet peas are greedy little plants and require lots of feeding to flourish. So, make sure you're planting them into well-prepared soil. A scattering of bone meal, a thick layer of compost or well-rotted manure, and a generous dose of natural fertiliser will do the trick, suggests the experts at Floret. Mix this deeply into the soil.
You'll also want to provide a structure for your sweet peas to climb up – such as an obelisk or trellis. These can make a pretty feature in themselves, and are perfect if you love our cottage garden ideas. Once this is in position, plant the seedlings out in rows around the structure. Sue Sanderson for Thompson & Morgan advises to place two or three seedlings in each hole for a nice, full display, planting each group about 15cm apart.
Happy sweet peas will grow fast – be sure to keep them in order by tying them to your structure as they grow, using pieces of string. Don't tie too tightly though, else you might damage the stems.
More top tips for growing sweet peas
- After sowing your seeds, stand the trays on a layer of gravel in the cold frame to deter slugs and snails.
- To keep hungry mice away, soak the seeds briefly in liquid paraffin as an effective deterrent.
- Slugs and snails will be attracted by their tender young growth, so regularly spray seedlings with slug and snail repellent to keep them safe.There's more advice on how to get rid of slugs in the garden in our guide.
- Too much warmth and not enough light leads to spindly growth. Pop your root trainers in a cool, light place for stronger plants.
- Poor ventilation is a common mistake that leads to fungal problems. When the weather is warm enough, open the greenhouse and cold frame to circulate air around your seedlings. Remember to close them again at dusk.
- Sweet peas love water, says the team at Floret, and need consistent moisture to thrive. They suggest to set up soaker hoses as soon as you plant them to keep them looking lush. Our best garden sprinklers can come in handy here, too.
- The team at Floret also advise to feed your sweet peas weekly once they're planted out, using a diluted fish and seaweed emulsion.
What is the best way to pick sweet peas?
For the longest vase life, pick sweet peas when there are at least two unopened flowers at the tip of a stem, says the team at Floret. Add flower food to the water to extend vase life.
Don't be shy when it comes to picking your sweet peas to enjoy indoors. Doing so actually encourages the plants to bloom for longer, as it stops them from going to seed. Be sure to keep on top of dead-heading, and remove seed pods as soon as possible too to help with this further, as says Sue Sanderson for Thompson & Morgan.
How do you collect sweet pea seeds for sowing?
If you're growing your own sweet peas this year, you might want to have a go at saving the seeds after they've flowered. Here's how to do it:
- Collect the seedpods and bring them indoors.
- Remove the seeds from the pods and let them dry for a few days on a layer of newspaper.
- Once dry, store them in an airtight container in a cool place until you want to plant them.
Where to buy sweet peas
It's easy to buy sweet peas as seeds or ready grown plug plants online or from garden centres. Use our quicklinks below to start shopping, or keep scrolling for some of our favourite varieties.
Where to buy sweet peas in the UK:
- Shop sweet peas at Amazon
- Shop sweet peas at Crocus
- Shop sweet peas at Dobies
- Shop sweet peas at Suttons
- Shop sweet peas at Thompson & Morgan
- Shop sweet peas at Waitrose Garden
- Shop sweet peas at You Garden
Where to buy sweet peas in the US:
- Shop sweet peas at Amazon
- Shop sweet peas at Burpee
- Shop sweet peas at Home Depot
- Shop sweet peas at Walmart
Sweet Pea 'King Size Navy Blue' from Thompson & Morgan
With dark navy flowers, this stunning variety will pack a punch in your summer displays. It will grow up to 180cm and spread to 30cm.
Sarah Wilson has been a lifestyle journalist for many years, writing about gardens since 2015. She's written for Gardeningetc.com, Livingetc, Homes & Gardens, as well as Country Homes & Interiors and Modern Gardens magazines.
Her own (small urban) garden is a work in progress - so many ideas, not enough space to cram them in. Hero plants include her ever growing collection of ornamental grasses, black bamboo and ferns, and the perennials like salvias and penstemons that come back reliably year after year. All very restrained though when in fact she'd love to pack her garden with gaudy dahlias and giant cannas, so these are top of her wish list for what to grow next.
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