How to Grow Sweet Peas: A Practical Guide from Seed to Flowers

Sweet peas are one of those flowers I wouldn’t want to be without. They give you a summer full of colour, make perfect cut flowers and, many have a delightful perfume.

You can sow sweet peas in autumn or spring, and both methods work perfectly well. Autumn sowing gives the plants more time to develop strong roots and can mean earlier flowers, while spring sowing is straightforward and avoids having young plants to look after through winter.

Sweet peas are usually climbers, so they’ll need something sturdy to grow up, along with regular watering once established. The other secret is picking. Once they start flowering, keep cutting them for the house and removing faded flowers. The more you pick, the longer they’ll keep going.

Give them a sunny position, decent soil and something to climb, and they'll reward you handsomely.

When to Sow

Sweet peas can be sown in autumn or spring, and I use slightly different approaches depending on when I'm sowing.

For autumn sowing, October and November are ideal. Sow the seeds in pots or deep modules and I keep them somewhere cool and protected, such as an unheated area in my  greenhouse or cold frame. They don't need very warm condition as the plants are better in these cool conditions overwinter. Most of the time I sow mine early in the year as I find the plants are in good condition to plant out.

Autumn-sown sweet peas develop good root systems over winter and are ready to grow away quickly when spring arrives. They can also flower earlier than spring-sown plants.

If you don't fancy looking after seedlings through winter, don't worry. Sow from January through to April instead. Early spring sowings can be started under cover, while later sowings need very little encouragement once temperatures improve.

I wouldn't get too hung up on which method is "best". Autumn sowing gives you a head start; spring sowing is simpler. Both can give you masses of flowers.

Sowing Sweet Peas

Sweet pea seeds are large and easy to handle, so sowing them is straightforward.

Use deep pots, root trainers or modules where possible because sweet peas quickly produce long roots. Fill them with a good multipurpose or seed compost and sow the seeds around 2–3cm deep.

I normally put two seeds into a small pot.

Water after sowing and allow the excess to drain. Keep the compost moist, but don't leave it permanently soaking wet.

You'll sometimes see advice to soak sweet pea seeds overnight or nick the seed coat before sowing. I've generally found that fresh seed germinates perfectly well without much fuss. If a particularly stubborn seed hasn't germinated when its neighbours have, you can always give it a little more time.

Autumn-sown pots should be kept somewhere cool and sheltered. Spring sowings appreciate a little warmth to get them started, but once the seedlings appear, give them plenty of light and cooler conditions so they grow sturdy rather than becoming long and floppy.

Growing Seedlings On

Once sweet peas are growing, the aim is to produce short, sturdy plants with a good root system.

Autumn-sown seedlings will naturally slow down as temperatures fall. That's fine. You're not trying to produce enormous plants during December; you're building roots ready for spring.

Keep them somewhere sheltered from the worst winter weather but don't mollycoddle them in a heated house. An unheated greenhouse or cold frame is usually ideal. Water sparingly during cold weather, particularly if the compost is already damp.

When seedlings have developed several leaves, pinch out the growing tip above a pair of leaves. This encourages shoots to develop from lower down and usually produces a bushier plant.

Spring-sown seedlings can be treated in much the same way. Give them plenty of light and pot them on if they're becoming root-bound before it's time to plant outside.

Before planting out, harden off plants that have been grown under cover. Gradually introduce them to outdoor conditions over a week or two rather than moving them straight from a sheltered greenhouse into a cold, windy garden.

Preparing the Ground and Planting Out

Sweet peas are hungry plants so it's worth preparing the ground properly.

Choose a sunny, open position with fertile, moisture-retentive but well-drained soil. Dig in plenty of well-rotted compost or manure before planting. Sweet peas like moisture around their roots, but they don't want to sit in waterlogged ground.

Plant autumn-sown sweet peas outside in spring once conditions are suitable. Spring-sown plants can follow as they become established and the weather improves.

Space plants roughly 15–20cm apart.

Put your supports in before or when you plant. Sweet peas grow surprisingly quickly once they get going, and trying to build a support around a tangle of young plants is considerably harder.

We use a wigwam of canes which works well for us, but there are other options including pea and bean netting, trellis or strong mesh.  You might want to collect strong pea sticks as another option.

Water everything thoroughly after planting and keep an eye on young plants while their roots establish.

Supporting and Growing On

Sweet peas naturally climb using little curling tendrils, but they often need some encouragement at the beginning.

Gently guide young shoots towards their support and tie them in loosely if necessary. Once they've found the netting, twigs or mesh, they'll usually start climbing by themselves.

Keep weeds down around the base, particularly while the plants are young.

If you're growing sweet peas purely for enormous exhibition-quality flowers, there's a whole world of cordon training and removing side shoots you can get involved with. There is plenty of information available from specialist societies to help you if this is your aim. For normal garden growing, I wouldn't bother. You will get plenty of flowers with less maintenance and planty of picking.

As the plants grow, make sure their supports remain secure. A wall of sweet peas covered in foliage and flowers catches a surprising amount of wind particularly where we live.

Watch for slugs and snails around newly planted seedlings too. A mature sweet pea can cope with some damage; a small plant with its growing shoot eaten off has a much harder time.

Once flowering starts, regular picking becomes one of the most important jobs.

Watering and Feeding

Sweet peas grow best when they have reasonably consistent moisture, particularly once they're growing strongly and beginning to flower.

Water thoroughly during dry spells. Don't just wet the surface — you want moisture reaching the roots. Plants growing against a fence or wall can be particularly easy to miss because those areas sometimes receive less rain than you think.

Container-grown sweet peas need closer attention. A large pot full of mature climbing plants can dry remarkably quickly during warm weather.

A mulch around the base helps conserve moisture and keeps the roots a little cooler.

Once flower buds begin appearing, an occasional high-potash liquid feed can help keep plants flowering strongly, particularly those growing in containers. A tomato feed is perfectly suitable when used according to the instructions.

Don't compensate for dry soil by pouring on more fertiliser. Water comes first.

Good soil preparation at planting time, followed by sensible watering and feeding once flowering begins, is usually all they need.

Flowering and Picking

Once sweet peas start flowering, keep picking them.

This isn't simply an excuse to fill the house with flowers. Regular cutting encourages the plants to continue producing more blooms.

Pick stems when several flowers are open but there are still buds waiting to develop. Early morning or evening is a good time, particularly during hot weather.

If you're not cutting the flowers for the house, remove faded blooms before they develop seed pods.

Once sweet peas start putting their energy into producing seed, flowering begins to slow down. Missing a few flowers isn't disastrous, but allowing lots of pods to mature is one of the quickest ways to bring your display towards an early finish.

During peak summer, I like to go over the plants every few days. It's surprising how quickly new flowers appear.

Eventually the plants will naturally begin to tire, particularly during prolonged hot, dry weather. But with regular watering, feeding and picking, you can keep them flowering for a remarkably long time.

Common Problems

Slugs and Snails

Young sweet pea plants are particularly vulnerable to slugs and snails. Keep an eye on newly planted seedlings, especially during damp weather. Once the plants are established and climbing strongly, a little leaf damage is usually much less serious.

Powdery Mildew

A white powdery coating can appear on foliage, particularly later in the season. Dry roots, poor airflow and warm conditions can encourage mildew.

Keep plants properly watered and avoid packing them too tightly together. A little mildew towards the end of summer isn't unusual and doesn't necessarily mean the plants have finished flowering.

Aphids

Aphids can gather around tender young shoots and flower buds. Check plants regularly and deal with small colonies before they become established. Often they can simply be rubbed off or washed away with water, while ladybirds and hoverfly larvae will help too.

Buds or Flowers Dropping

Very hot weather, dry roots or sudden changes in conditions can cause flowers and buds to struggle. Consistent watering during warm weather makes a big difference.

Lots of Leaves but Few Flowers

Overfeeding with nitrogen can produce masses of healthy green growth at the expense of flowers. Once plants are established, avoid high-nitrogen feeds and use a high-potash feed when additional feeding is needed.

Plants Not Climbing

Young sweet peas sometimes need a little help finding their supports. Loosely tie shoots towards the netting or canes until their tendrils take hold.

And don't worry if your autumn-sown sweet peas look rather unimpressive during winter. Keep them cool and protected, and once spring arrives you'll usually see why you gave them that early start.