When to Plant Sweet Peas

Sweet peas can be sown either in autumn or in spring. Autumn sowing, usually in October or November, gives plants a head start, allowing them to develop strong roots over winter. However, these young plants need protection from harsh frosts, typically in a cold frame or unheated greenhouse. For most UK gardeners, the more traditional spring sowing between January and April is reliable and easier to manage. If sowing directly outdoors, wait until the frost risk has passed, usually from March onwards.

How to grow sweet peas

Sweet peas are climbers that thrive in full sun and fertile, moisture-retentive soil. They need support from the beginning, such as canes, netting or trellis, to help them grow upright and stay healthy. Sow seeds in deep pots or root trainers, as sweet peas develop long taproots. Keep the compost moist and once the seedlings have two or three pairs of leaves, pinch out the tips to encourage bushier growth. Regular watering and feeding will ensure a long flowering season.

How to grow sweet peas at home

Growing sweet peas at home is straightforward and rewarding. Choose a bright, sheltered spot that gets at least six hours of sunlight daily. They grow well in borders, raised beds, or deep containers on patios and balconies. Adding compost or well-rotted manure to the planting area improves flowering performance. If starting seeds indoors, place the pots in a cool, well-lit room. Once plants reach a suitable size and the weather has warmed up, harden them off before planting outside.

Planting sweet peas

When planting out sweet peas, dig a generous hole to accommodate the root ball and space each plant around 20 to 30 centimetres apart. Plant them deeply to support strong root development. Water thoroughly after planting and add supports at the same time to avoid damaging the roots later. Tie the stems in gently as they grow. In pots, use a deep container with rich compost and a central support like a wigwam for them to climb.

Caring for sweet peas

Sweet peas need consistent care throughout the growing season. Keep the soil evenly moist, especially during dry spells, and feed fortnightly with a high-potash fertiliser once the buds start forming. To prolong flowering, regularly pick the blooms or deadhead spent flowers before they set seed. If left to go to seed, the plant will stop producing new flowers. Pinching out young plants early and tying them in as they climb helps them stay strong and manageable.

Growing sweet peas

Sweet peas prefer cooler growing conditions, so early planting works in their favour. They dislike extreme heat or drying winds. A well-prepared site with compost-rich soil and regular care will reward you with weeks of vibrant blooms. Support their rapid vertical growth and keep on top of watering and feeding. Whether you're growing in the ground or containers, the same principles apply: sun, space, support and regular picking.

Where to buy sweet peas

Sweet pea seeds are available from most garden centres, but for a broader selection, specialist seed suppliers are worth exploring. UK-based companies often offer curated mixes for scent, cut flowers or unusual colours. These suppliers also tend to provide better quality control and germination rates than supermarket multipacks. Online ordering is convenient and allows you to access heirloom or heritage varieties not commonly found in-store.

Sweet pea varieties to grow

There’s a wide variety of sweet peas to suit different garden styles and needs. Some are compact and ideal for containers, while others are vigorous climbers best suited to open beds or fences. Older varieties often offer the best scent, while newer cultivars have been bred for larger blooms and improved weather resistance. Choose a mix that balances fragrance, colour and form for the most satisfying display.

Best sweet peas for cut flowers

For cutting, choose varieties that produce long, strong stems and plenty of flowers. These are often from the Spencer group, known for their large, ruffled blooms. Sowing in blocks rather than rows helps encourage straight stems. Regular picking not only keeps the plants blooming but also ensures a steady supply of fresh flowers for vases. Sweet peas respond well to this kind of routine harvesting.

Best sweet peas for scent

If fragrance is your main goal, traditional varieties often deliver the strongest scent. These are ideal near seating areas or entrances where their perfume can be appreciated. While newer hybrids often focus on colour and size, many retain excellent scent profiles too. Look for heritage lines that have stood the test of time in cottage gardens and cut flower arrangements alike.

How to sow sweet peas

To sow sweet peas, fill deep pots or root trainers with seed compost and plant the seeds about two centimetres deep. If the seed coat feels hard, soaking them in water overnight can improve germination. Place pots in a cool, bright spot and keep the compost just moist. Germination usually takes a week or two. Once the seedlings emerge, keep them growing steadily in cool conditions to avoid legginess.

Planting out sweet peas

When the plants are around ten to fifteen centimetres tall and the risk of frost has passed, you can begin planting them outside. Acclimatise them first by hardening off—gradually introducing them to outdoor conditions over a week. Choose a sunny spot with enriched soil and space them well apart. Water thoroughly after planting and secure their stems to supports to guide their upward growth. Keep an eye on them in the early days to make sure they establish quickly.

Why autumn sowing is worth the effort

Autumn-sown sweet peas tend to produce earlier, stronger blooms. By sowing in October or November, you give the plants time to develop long, deep roots through the cooler months. While they won’t grow much above ground over winter, their underground progress sets them up for a fast start come spring. This approach works best in milder regions or with protection, such as an unheated greenhouse or cold frame. In colder areas, it’s still possible—but covering the seedlings with cloches or fleece is a must during hard frosts.

Daylight matters more than temperature

Many gardeners focus solely on soil temperature, but sweet peas are also influenced by day length. Longer days in spring naturally trigger stronger growth and budding, which is why seeds sown in March or early April tend to catch up quickly with those started in autumn. If you miss the autumn window, don’t worry—spring sowings still produce excellent results, especially when supported by good light and regular care.

Indoor vs. outdoor sowing: pros and cons

Indoor sowing gives you better control over temperature and moisture, which leads to higher germination rates and healthier seedlings. You can start earlier, protect the plants from pests, and harden them off when ready. The downside is that it takes more effort, space, and the extra step of acclimatising plants to outdoor life.

Outdoor sowing is lower maintenance and more natural—but seeds are at the mercy of slugs, birds, frosts and cold soil. If choosing this route, wait until the soil has warmed and conditions are settled, ideally from late March to mid-April.

Don’t panic if sowings go wrong

If your first batch of seeds fails to germinate or young plants get caught by a late frost, you can resow sweet peas well into April or even early May. These later sowings will flower slightly later in summer but will still put on a good show, especially in warmer years. Sweet peas are forgiving and grow quickly when given decent conditions.

Using sweet peas in a cut-and-come-again system

The more you pick sweet peas, the more they flower. If you sow at staggered intervals—once in autumn and again in spring—you can extend your harvest window and maintain a more constant supply of blooms. This is especially useful if you’re growing sweet peas for events, markets or personal bouquets.

Hardening off is non-negotiable

Whether you sowed in October or March, any sweet peas grown indoors or in a greenhouse need to be hardened off before going into the ground. This step often gets rushed or skipped, but it’s vital. Over 7–10 days, gradually expose your seedlings to the outdoors during the day and bring them in at night. Doing this helps prevent shock and toughens them up for life outside.

Planning for different bloom times

Different sweet pea varieties bloom at slightly different times. Early types, like heritage or Grandiflora varieties, tend to flower sooner and are excellent for autumn sowing. Modern Spencer varieties take a little longer to mature but offer large, showy blooms ideal for cutting. Mixing types ensures a longer flowering season and a more dynamic display.