how to grow sweet peas banner

How to Grow Sweet Peas

About Sweet Peas


The sweet pea is a quintessential cottage garden favourite that has stood the test of time. Adored for charismatic and dainty blooms, its ability to add height to borders when grown up obelisks, and the perfect plant for cut flowers, these charming annuals are the definition of summertime.


Many sweet peas are highly fragrant, which adds to their appeal.


  • ‘Grandiflora’ types represent the gold standard for traditional blooms and although flowers can be smaller than modern varieties, they pack a punch for fragrance.


Unwins Sweet Pea Aurora Borealis Seeds


  •  ‘Spencer’ types are the bloom of choice for exhibitors, as their long stems and large flowers are borne in a vast array of colours – although perfume can vary.


  •  Dwarf sweet peas are a winner in hanging baskets and pots, enabling anyone to grow these exquisite blooms – even if you don’t have a garden.


Unwins produce many types of sweet peas, take a look at the full range here.

The rate at which sweet peas reach for the skies makes them a top choice when it comes to getting children hooked on gardening, while the scale of colours on offer – including red, white, blue, pink and pastel shades – makes it easy to put on a spectacular display. You don’t even need to go to the cost of buying obelisks and trellis, as sweet peas will scramble up twiggy sticks in sunny borders.


It’s worth looking out for varieties that carry the Royal Horticultural Society’s coveted Award of Garden Merit (AGM), the hallmark of great garden performance. When it comes to sweet pea seeds, Unwins Seeds has a rich heritage. The company has grown sweet peas since 1903 and stocks around 40 varieties, so there’s a bloom to suit every gardener’s taste.


Try Unwins’ latest introduction, sweet pea ‘Platinum Jubilee’ – with stunning blue stripes on a white background. Named to honour the late Queen Elizabeth II’s 70 years on the throne in 2022, it’s a Spencer type with fantastic fragrance. For deliciously scented blooms of yesteryear, sow Unwins’ sweet pea ‘Old Fashioned Selection’. These are Grandiflora types which were popular toward the end of the Victorian era, with dainty flowers in a host of shades that work wonders for cutting.


To learn more about sweet peas, visit The National Sweet Pea Society, a charity dedicated to these wonderful flowers!


Unwins Sweet Pea Platinum Jubilee

When to Sow

Unlike many bedding plants that are sown in the run-up to Easter, it’s good practice to sow annual sweet peas in late autumn, from October to November. Autumn-sown plants have time to grow and develop over winter, resulting in more robust plants that begin to flower earlier in the season. Don’t worry if you’ve left it late, however, as sweet peas can also be sown between January and March, and you’ll be rewarded with flowers that carry on later into the summer. Seed can even be direct-sown outdoors between April and May. Sowing in both autumn and spring will guarantee a long season of colour in the garden.

How to Sow


  1. Sweet peas develop extensive root systems, so deep, thin pots known as ‘root trainers’ are a must. Try a Gro-Sure Visiroot 4 Cell Deep Kit, this been custom-designed for sweet peas, to encourage healthy roots with minimal disturbance.
  2. Fill the seed cells with a quality growing media such as Gro-Sure Seed & Cutting Compost, and gently firm the compost down.
  3. Sow sweet pea seeds individually in each cell, pushing the seed around 2cm deep and covering it with compost.
  4. Moisten the compost using tap water and place in a propagator or on a warm window sill. Keep propagators at a temperature of around 10-15°C and refrain from watering again until seedlings emerge.
  5. Once seedlings appear, remove the propagator lid and grow in cooler conditions, with a minimum temperature of 5°C. Cool, sheltered, frost-free environments such as a well-lit porch, cold frame or unheated greenhouse are ideal for promoting root growth over winter.


Next steps


  1. To prevent plants from becoming leggy (tall and spindly), pinching out is essential. Once plants are 7-10cm tall, pinch out the shoot tips. It sounds brutal, but will encourage healthy, well-balanced plants.
  2. Sweet peas raised indoors will need hardening off – acclimatising to outdoor growing conditions – for at least two weeks before planting out. Stand plants outdoors on mild days, when weather conditions are good, before bringing back indoors ahead of nightfall.
  3. After hardening off, spring-sown sweet peas should be planted out after the worst of the frost is over: usually April, perhaps later in colder regions. Autumn-sown sweet pea plants can go out earlier, from the end of March. Sweet peas tolerate light frosts once hardened-off.
  4. Ahead of planting, select a sunny site with fertile, well-drained soil. Digging-in well-rotted manure such as Gro-Sure Farmyard Manure (or well-rotted garden compost) ahead of planting will boost soil fertility and moisture-retention. Raking in a general-purpose fertiliser such as Growmore will also improve nutrient levels.
  5. Water well before planting out, setting young plants 20-30cm apart (and around 5cm from their supports). You’ll need to provide plenty of support, such as twiggy sticks and canes, or a wigwam, obelisk or trellis to help them get going.
  6. Keep plants well-watered after planting and watch out for pests, as young growth is susceptible to slug and snail damage.
  7. As sweet peas begin to grow, tie plants to their supports once a fortnight.
  8. Established plants will need regular deadheading and plenty of water during dry spells. Regular feeding with a liquid fertiliser such as Westland Boost will ensure that gorgeous displays of flowers keep coming throughout summer. Or use a potash-rich tomato feed such as Big Tom Tomato Food, every couple of weeks.


Where spent blooms are left to set seed, plants will rapidly stop flowering. To ensure that displays don’t go over prematurely, regular deadheading of faded flowers is essential. Any seed pods must be removed without delay. Frequent cutting of fresh blooms for the vase is perhaps the best way to encourage further flushes of flowers.

Common Problems, Pests & Diseases

Young sweet peas are vulnerable to slug and snail attack when first planted out into the garden, so protect using an organic slug control.

Drought and hot, dry conditions can prompt outbreaks of powdery mildew, so keep plants well-watered when the mercury soars.

Watch out for aphids, which love to suck sap from sweet peas, especially around the tips of shoots and flowers. Blast those bugs off with a burst of water from your hosepipe. 

Where plants show signs of rot, it’s a signal that soil is too heavy or waterlogged. Take care to plant into fertile, well-drained soil.

High temperatures can take their toll on sweet pea foliage. Try to avoid wetting plants when watering, as foliage is easily scorched, and water plants first thing in the morning when temperatures are cooler.

Frequently Asked Questions

Can sweet peas be planted to brighten up shady parts of the garden?

No. Sweet peas are sun-lovers, and plants grown in shady conditions are likely to put on disappointing displays of flowers.

Why have buds dropped from plants?

Bud drop is a sign of temperature stress, often caused by low temperatures after planting out. Make sure plants raised indoors are properly hardened off before planting out, to reduce the risk.

Will sweet peas come back next year?

Annual sweet peas (Lathyrus odoratus) grow, flower, set seed and die in the space of a year, so treat in the same manner as summer bedding, composting plants after displays are over. You’ll need to grow perennial species (Lathyrus latifolius) for displays that come back in subsequent years, although they lack the fragrance that many gardeners enjoy. Have a look at our perennial sweet pea Unwins Sweet Pea Lord Anson's Blue Pea

Why have young plants fallen from canes or obelisks?

Sweet peas need the support of fine netting attached to canes or an obelisk for their tendrils to attach easily. Or they need to be tied to the support using twine.


Back to Learn & Grow