How to Grow Sweet Peas (Fragrant Climbers)

Few flowers reward a gardener like sweet peas (Lathyrus odoratus). These old-fashioned annual climbers scramble up a trellis on slender tendrils, unfurling ruffled blooms in shades of plum, blush, lavender, and cream — and their perfume can fill a whole corner of the garden. The catch is that sweet peas are cool-season plants with strong opinions about timing, so a little planning up front makes the difference between a wall of flowers and a few sad, leggy stems.

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This guide walks you through everything from choosing seeds and getting them to germinate, to building a support, feeding for length and fragrance, and keeping the plants blooming as long as the weather allows. Sweet peas are not difficult — they simply ask you to work with the seasons rather than against them. For more on annuals and perennials of every kind, see our plant & flower care guide.

Meet the sweet pea: a cool-season climber

Sweet peas are hardy annuals, which is a useful phrase to understand. “Annual” means they complete their whole life — seed to flower to seed — in a single growing season. “Hardy” means the young plants tolerate frost and actively prefer cool weather. Put those together and you get a flower that does its best growing in the chilly, damp shoulder seasons of the year, not in the heat of midsummer.

This is the single most important thing to internalize. Many gardeners treat sweet peas like marigolds or zinnias — warm-season flowers you sow after the last frost — and then wonder why they get spindly plants that quit by July. Sweet peas want the opposite. They want to be growing roots while the air is cold, so they’re large and established by the time mild spring weather arrives.

Plants typically climb 6 to 8 feet given a tall enough support, clinging by curling tendrils rather than twining stems. Modern breeding has produced everything from heavily scented heirloom varieties to large-flowered “Spencer” types with frillier blooms but sometimes less perfume. If fragrance is your priority — and for most people it is — read the variety descriptions carefully and lean toward the old-fashioned and heirloom strains.

When and how to sow

Choosing your sowing window

There are two main sowing windows, and which one suits you depends on your climate:

• Fall sowing (mild-winter regions, roughly USDA zones 7 and warmer): Sow in autumn so plants establish over winter and bloom early the following spring. Young plants overwinter happily under cold frames or even in the open ground in the mildest areas.
• Late-winter / early-spring sowing (cold-winter regions): Start seeds indoors or in an unheated greenhouse in late winter, then plant out while it’s still cool. This is the safest route for most of the US, the UK, and anywhere with hard freezes.

The general aim is the same in both cases: get the plant growing strong roots in cool conditions so it can power through a long bloom season before summer heat shuts it down.

Soaking and chitting the seeds

Sweet pea seeds have a hard outer coat, and germination can be slow or patchy if you simply drop them in soil. Two simple tricks help enormously:

• Soaking: Soak seeds in room-temperature water for several hours (overnight is fine). They’ll swell as they absorb moisture. Sow the plump ones; some growers discard any that still look hard and shriveled.
• Chitting: For stubborn varieties, “chit” the seeds by laying them on damp paper towel inside a covered container in a warm spot. Check daily, and as soon as a tiny white root tip emerges, sow that seed point-down into a deep pot.

Because sweet peas grow long taproots, they resent being cramped. Deep, narrow containers called root trainers (or even toilet-roll tubes stood in a tray) give the roots room and make transplanting far less of a shock. You can find purpose-made root trainers for deep-rooted seedlings that open like a book so you slide plants out without disturbing the roots. Start with quality fragrant sweet pea seeds in colors you love, sowing one or two per cell about an inch deep.

Pinching for bushy, productive plants

Left to their own devices, sweet pea seedlings often shoot up as a single weak stem. Pinching fixes this and is one of the highest-payoff things you can do. When a seedling has developed three or four pairs of leaves, simply nip out the very top growing tip with your fingertips, just above a leaf pair.

This stops the upward rush and signals the plant to send out multiple side shoots from lower down. Instead of one thin vine, you get a bushy plant with several strong stems — and more stems means more flowers. The plant may sulk for a few days, but it bounces back stronger. Don’t skip this step out of squeamishness; experienced cut-flower growers pinch every single seedling.

This same “remove the tip to encourage branching” logic shows up across the flower garden. The companion practice of removing spent blooms is just as important once plants mature — see our guide on how to deadhead flowers for the broader principle.

Sun, soil, and the right spot

Light

Sweet peas flower best in full sun — at least six hours of direct light a day. In hot-summer climates, a position that gets bright morning sun but a little afternoon shade can actually extend the season by buffering the plants from extreme heat. In cooler regions, give them all the sun you can.

Soil

These are hungry plants with deep roots, and they reward rich, well-prepared ground. The classic advice is to dig a generous amount of well-rotted compost or aged manure into the planting bed before setting plants out. Sweet peas like soil that holds moisture but still drains — soggy, waterlogged ground invites rot, while bone-dry sand starves them.

• Work in plenty of organic matter to a good depth — the roots travel far down.
• Aim for a near-neutral pH; sweet peas dislike strongly acidic soil. A little garden lime helps in acidic regions.
• If growing in containers, choose the largest, deepest pot you can and use a rich, quality potting mix.

Support and training

Sweet peas are climbers, and they need something to climb from the start. They grip with tendrils, so they need relatively thin supports those tendrils can wrap around — a solid post or wide board won’t work on its own. Good options include:

• Trellis netting stretched between posts — easy and very effective.
• Twiggy “pea sticks” (branched prunings pushed into the ground) for a natural cottage-garden look.
• Bamboo cane wigwams or obelisks for a freestanding feature in a border or large pot.
• Wire or string grids against a sunny fence or wall.

Whatever you choose, make it tall — 6 feet or more — and put it in place before or as you plant, so you’re not driving stakes through established roots later. A roll of garden trellis netting for climbers is inexpensive and reusable season after season.

Young plants often need a gentle nudge to find their support — loosely tie the first few inches of growth to the netting with soft twine until the tendrils take over. After that they largely climb themselves, though you may occasionally tuck a wandering stem back in. If you enjoy training climbers, you’ll find the same satisfaction with perennial vines like those in our clematis care guide.

Watering, feeding, and keeping them blooming

Water

Steady moisture is key. Sweet peas have a lot of leaf and flower to support, and they don’t like to dry out — drought stress causes buds to drop unopened and shortens the season. Water deeply and regularly, especially once flowering begins and as the weather warms. Aim the water at the base of the plants rather than over the foliage to reduce the risk of mildew. A mulch around the roots helps lock in moisture and keep the soil cool.

Feed

For the longest stems and most flowers, feed established plants every week or two during the blooming season. Use a fertilizer that isn’t too high in nitrogen — too much nitrogen drives lush leaves at the expense of flowers. A balanced or slightly potassium-rich liquid feed (the kind sold for tomatoes works well) encourages plenty of blooms. Don’t overdo it; consistent moderate feeding beats occasional heavy doses.

The cut-and-come-again habit

Here’s the trait that makes sweet peas so beloved by cut-flower gardeners, and the one most likely to trip up beginners. Sweet peas are “cut-and-come-again”: the more you pick, the more they bloom. But the reverse is also true and unforgiving — if you stop picking and let blooms fade into seed pods, the plant decides its job is done and stops producing new flowers.

An annual’s entire biological mission is to set seed. Every pod that forms is a signal to the plant that it has succeeded and can wind down. So your job is to never let that happen during the season:

• Pick flowers often — every few days at the height of the season. Cut long stems for the vase while the lowest flowers on the stem are just opening.
• Remove any seed pods you spot immediately. Even a few pods can slow the plant dramatically.
• Deadhead blooms you didn’t cut before they go to seed.

Treated this way, a healthy row of sweet peas produces armful after armful of fragrant stems for weeks. This generous, pick-me habit is exactly why they appear on nearly every list of the best cut flowers to grow. As a bonus, the more you bring indoors, the more the plant pushes out — picking is the chore that gardeners actually look forward to.

When heat ends the season

No matter how diligently you pick, sweet peas are ultimately defeated by heat. Once sustained hot weather arrives — daytime temperatures consistently in the high 80s Fahrenheit and up, with warm nights — flowering slows, colors fade, stems shorten, and the plants begin to look tired and yellow. This is normal and expected; it’s not a failure on your part.

You can stretch the season a little by keeping plants well watered and mulched, siting them where they get afternoon shade in hot climates, and choosing more heat-tolerant varieties. But eventually it’s time to let go. When the plants are clearly spent, pull them and compost the foliage. If you want seed for next year — and you’ve grown an heirloom (non-hybrid) variety — leave a few pods at the very end of the season to ripen and dry on the plant, then save the seed.

In regions with mild summers and cool coastal influence, the season runs longer; in hot inland climates, it can be frustratingly short. Either way, the trick is to start early enough that the plants are big and blooming before the heat arrives. Sweet peas are a sprint, not a marathon — plan around their calendar and they’re one of the most rewarding flowers you can grow.

Frequently asked questions