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Home & garden.

30 September 2021

How to grow sweet peas

Sweet peas are annual climbers with unbeatable fragrance. Discover our best sweet pea varieties and tips for how to grow them.
CT
Ceri Thomas
Sweet peas

The frilly, perfumed blooms of sweet peas, held on long, straight stems, make perfect cut flowers. Plus, the more you pick them, the more buds form to make fresh flowers. They’re easy to grow as well. Most are climbers, which can be trained up teepees of canes, but you can also buy dwarf varieties for pots and baskets.

Which? Gardening magazine grew a range of popular varieties to see which would give us the best display.


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Key facts

Plant type Hardy annual climber 

Position In a sunny border climbing up a fence or obelisk 

Soil Any

How to grow sweet peas: month by month

January
February
March
April
May
June


SOW
PLANT

FLOWERING
July
August
September
October
November
December
FLOWERING
FLOWERING

SOW


Best sweet pea varieties

Which members can log in now to see the full results and which are our Best Buy varieties. If you're not a member, join Which? to get instant access.

Best Buy sweet peas for scent
What it looks like
Variety name
Height x spread
180 x 40cm
This RHS Award of Garden Merit (AGM) holder was a strong grower that produced plenty of very large ruffled blooms. Paler varieties often carry the best scents, but the deep-pink and white flowers on this variety were deeply perfumed and popular with visitors to the trial beds. The stems were long and strong, making them suitable for cutting. Regular deadheading meant the blooms kept coming, giving a lovely display. Peak flowering: Jun-Aug
What it looks like
Variety name
Height x spread
180 x 40cm
This variety produced large pure-white flowers, which were slightly ruffled and had a gorgeous scent that was extremely popular with visitors to our trial beds at Capel Manor. It was a vigorous variety, untroubled by the virus that affected some other plants. The frilly blooms had long stems, making it ideal for vases, and they kept coming for as long as the plant was deadheaded, from June into August.  Peak flowering: Jun-Aug
Best Buy sweet pea mixes
What it looks like
Variety name
Height x spread
180 x 40cm
The smaller blooms on this sweet-pea mix were very elegant, and although the colours were more vibrant than the pastel shades we were expecting, the overall effect was still charming. The mix contained a very pretty sweet pea with a fuchsia-pink bottom petal and a cerise top petal, creating a brighter note among the mix of mauve-freckled, pink freckled and bicoloured burgundy and purple sweet peas. The scent was nice, developing more as the flowers matured. Peak flowering: Jun-Aug
What it looks like
Variety name
Height x spread
180 x 40cm
If you’re looking for a mix of sweet peas in different colours that blend well together, try this variety. It gave us a lovely balanced blend of marbled pink, dark pink, lilac and two-tone purple and burgundy blooms – an impressive result from six plants. The mix was cheerful, fragrant and floriferous, too, covering the obelisk in blooms and creating a lovely display.   Peak flowering: Jun-Aug
Best Buy grandiflora sweet peas
What it looks like
Variety name
Height x spread
210 x 80cm
For eight weeks through summer, this modern variety produced lots of large, pale-blue flowers on long, thick stems with wavy petals and a great scent. This was a very attractive variety and a firm favourite with our assessors who thought that they’d not only give a great display in the garden but also be perfect to use as cut flowers. Peak flowering: Jun-Jul
What it looks like
Variety name
Height x spread
220 x 100cm
This is a modern variety bred for its potent aroma and it didn’t disappoint. It began flowering in June, producing masses of large, frilly flowers with a lilac edge, and a strong scent, on long, thick stems. Their scent could easily fill a room with perfume. We grew it alongside a newer variety, which is reputed to have a stronger scent but found them impossible to tell apart. We thought you’d be just as happy growing either. Peak flowering: Jun-Aug
What it looks like
Variety name
Height x spread
210 x 90cm
This variety is said to be the original sweet pea and was named after the Sicilian monk who discovered it. This heirloom type had small bi-coloured flowers and a potent scent that was noticeable from quite a distance. The plants were covered with masses of flowers from top to bottom for nine weeks, which would make them an excellent variety for any garden. It has definitely stood the test of time and is still a favourite for many.  Peak flowering: Jun-Aug
What it looks like
Variety name
Height x spread
220 x 100cm
This is a popular heirloom variety. Its flowers were presented on slightly shorter, thinner stems than the modern varieties, but that didn’t detract from the display it provided in the garden. They were very vigorous plants, quickly scrambling up, over and covering their supports with a dense mass of stems. They were soon covered from top to toe with masses of pleasantly scented and striking flowers whose petals were marbled with purple and white. This was the best ‘flaked’ type we tried this year. Peak flowering: Jun-Aug
Best Buy sweet peas for pots
What it looks like
Variety name
Height x spread
20 x 50cm
With one of the longest flowering periods in our trial, this variety deserves a Best Buy. It formed neat, compact, dome-shaped plants that trailed gracefully over the edges of our hanging baskets, producing blooms in an attractive mix of light blue, violet, red, pink and purple. The fragrance was good, too, and our plants weren’t troubled by bad weather and didn’t succumb to powdery mildew.  Peak flowering: Jul-Aug
What it looks like
Variety name
Height x spread
25 x 40cm
We loved the velvet-textured, deep purple and violet flowers of this variety, which was the earliest and joint-longest flowering variety on test. The semi-domed habit looked great in containers with the moody-hued blooms held above and, although the fragrance wasn’t the strongest, the variety gained a Best Buy for its flower power. On top of this, it only suffered a tiny touch of powdery mildew towards the end of its flowering period. Peak flowering: Jul
What it looks like
Variety name
Height x spread
25 x 40cm
This mix produced short, compact plants with a domed and cascading habit that makes it ideal for hanging baskets or a large container. The blend of flower colours in white and shades and tones of pink and red was very attractive and, although not the longest flowering variety in our trial, it made an eye-catching display. We gave it full marks for its strong fragrance, which makes it a deserved Best Buy. Peak flowering: Jul

How we test sweet peas

We trialled a number of the different sweet pea varieties at our trial ground in North London. We sowed them in October and grew them in our coldframes through the winter until April, when we planted them outdoors. The varieties for pots were planted in pots and hanging baskets. The ordinary varieties were tied in and deadheaded weekly, and sprayed with insecticide to control aphids and prevent viruses spreading. Throughout summer we noted how strong the scent was, how much flower coverage the plants had and if any were affected by pests or diseases. We also assessed them for the length and thickness of their stems to see if any would be good for cut flowers.

Types of sweet peas

They’re divided into two groups: grandiflora and Spencer types. For an expert, the distinction is in the ‘keel’ petals (the lowest two petals) – grandiflora types have a ‘clamped’ keel, while Spencer types don’t. For the rest of us the difference is that Spencer types have big, frilly blooms and, despite their name, grandifloras have smaller flowers and stronger scents. 

Modern breeding has blurred these divisions. Nowadays, grandifloras are claimed to have both the big flowers and long stems we look for in cut flowers, as well as the profuse flowering and strong scent we love in the garden.

Sowing

Sow seeds during October in rootrainers or deep pots using a Best Buy compost for sowing seeds. There's no need to pre-treat seeds. Keep them at 16-18°C and they should germinate in 7-14 days.

Mice eat sweet-pea seeds, so cover the seed trays or pots with a propagator lid until they’ve germinated.

Caring for your plants

Overwintering

Once germinated, move them to a cool, sheltered position such as a coldframe. Young sweet peas like growing in cool conditions, but don’t tolerate being frosted. If it’s too warm they can become weak.

Planting

Plant them in March or early April against a support they can wrap their tendrils around, such as a teepee made of bamboo canes, then tie them in initially as they grow.

Picking the flowers

Pick sweet peas regularly to encourage them to keep blooming. At the end of the season, leave some flowers to set seed so you can collect it for sowing in autumn.

Common growing problems

Flower buds falling off

Wet soils, warm days and cold nights can make plants drop their buds. It’s nothing to worry about and they’ll soon recover as the nights warm up.

Virus

Sweet-pea viruses cause streaked flowers or mottled leaves. They are easily spread by aphids, so be sure to control them. Remove infected plants and clean secateurs between working on plants.

Read more about virus on sweet peas

Powdery mildew

In dry summers, powdery mildew can become a problem. Keep plants well watered but don’t wet the leaves. Spraying with a suitable fungicide can slow its spread.

Read more about powdery mildew