Sweet peas, Lathyrus odoratus, are one of the most popular annuals thanks to their strong scent and how easy they are to grow.
Unlike most bedding plants, they are climbers and so need support to grow on. They are a staple of beds of flowers for cutting, and informal cottage garden designs.
Table of Contents
Growing Sweet Peas from Seed
There are two main ways to sow sweet pea seeds: either start them off in a greenhouse when it’s still too cold to plant them out, or sow them directly into the soil when it’s warm enough.
The earlier you start them, the bigger and better your flower display will be.
1. Sowing in a Greenhouse (Autumn or Early Spring)
- Timing: Sow the seeds in Autumn or early Spring, about 6-8 weeks before the last expected frost.
- Preparation: Use seed trays filled with well-draining potting mix. Moisten the soil before sowing.
- Sowing: Plant the seeds about 2.5cm deep, spaced 5-8cm apart.
- Environment: Place the trays in a greenhouse or a sunny windowsill where temperatures remain mild.
- Watering: Ensure consistent moisture but avoid waterlogging. A light misting can help keep the humidity up.
- Transplanting: Once the seedlings are about 10cm tall and hardened off, transplant them into pots or directly into your garden after the last frost.
2. Direct Sowing into the Soil (Late Spring)
- Timing: Wait until late Spring, after the danger of frost has passed. Soil temperatures should ideally be around 10°C (50°F).
- Soil Preparation: Choose a sunny spot with well-drained, nutrient-rich soil. Loosen the soil and incorporate some compost or well-rotted manure to enhance fertility.
- Sowing: Plant seeds about 2.5cm deep, spacing them 15cm apart for optimal growth and airflow.
- Watering: Water gently after sowing to settle the seeds in place. Keep the soil consistently moist until germination.
- Thinning: Once the seedlings emerge, thin them out to the strongest plants, leaving about 15-20cm between each one for ample space.
Buying Sweet Pea Seedlings in Jumbo Plugs
To skip all that seed sowing, buy our sweet pea seedlings in jumbo plugs.
Just follow our easy sweet pea planting instructions to get started.
Sweet Peas and Late Frosts
Sweet peas are frost-hardy annuals, so there is no need to worry if a “normal” overnight late frost in the range of -1 to -4 degrees Celsius is forecast.
If temperatures dip below that, or if there is a prolonged spell of cold weather where the temperature does not rise above freezing for several days, you may want to assist your plants.
- If they are still in pots or root trainers:
- Move them into an unheated greenhouse, conservatory, garage, or shed.
- If they are already planted:
- Protect your sweet peas with horticultural fleece.
- Keep the fleece in place until the freeze is over.
Supporting Sweet Peas
Sweet peas are natural climbers and require support structures. It’s good to get the supports in place before you plant them, especially if you are growing them in pots, where it’s usually easiest to put your support structure within the pot before planting.
- Push long canes into the ground in a circle, spacing them 10-15cm apart.
- Pull them together at the top and tie them to create a wigwam/tipi structure.
- Purchase metal or woven willow frameworks/obelisks for longlasting garden features.
- Create your own screen with:
- Two sturdy stakes at either end.
- 2-3 wires stretched between them at even intervals.
- Cane, hazel switch, or bamboo driven into the soil every 20-30cm to secure to the wires.
- Utilize a variation of method three by setting up:
- Two stout fence posts about 2-3 meters apart.
- Chicken wire (180cm wide) or plastic pea/bean netting stretched between them.
When growing from seed, the RHS recommend using a snazzy starter frame (which we don’t sell) attached to the pot, which you plant out with the seedlings.
Growing Sweet Peas
Soil & Sun Requirements
- Sweet peas need plenty of sun.
- Although their roots fix nitrogen and will survive in poor soil, you want your plants to positively thrive!
- Prepare the soil by incorporating well rotted compost or manure to improve fertility and moisture retention.
The two main sweet pea growing styles
- Normal Garden Way: Easy, gives you a great bunch of sweet peas for summer enjoyment.
- The Exhibitor’s Way: A bit time-consuming, gives you fewer, bigger blooms with immaculate, straight stems.
For first-time growers, beginning with the normal garden way is recommended.
Whichever way you choose, encourage luscious blooming
- Regularly picking flowers, which stimulates new growth and prevents seed pod formation
- Cutting back some little curly tendrils that sweet peas use for grip, as these expend energy directed toward flower production
- Feeding every two weeks with high potassium and phosphorous fertiliser, tomato or comfrey fertiliser is good, but if the plants are mulched with a rich compost or manure, it’s not necessary
- Watering well during dry spells
- As the season continues, it’s normal for smaller flowers to appear on shorter stems
Normal Garden Growing Method
- Plant a couple of plants about 5cm away from their intended support
- Dig a hole approximately twice the size of the root ball
- If gardening in very dry sandy soil, place strips of damp newspaper at the bottom of the hole
- Position the sweet pea plug in the hole and cover it with soil up to the first side shoot
- Firm the soil around the roots, without crushing the plug
- Water thoroughly
- As soon as possible, tie the shoots to the support using flexi ties, sweet pea rings, or garden twine
- Initially, this may need to be done every couple of weeks, then more often as the season progresses
- Prune off stray shoots growing the wrong way and if your framework becomes too crowded
The Exhibitor’s Professional Growing Method
Professional growers and people competing at their village flower show care about quality over quantity: they want great big flowers on perfect, long, straight stems.
To achieve this, they typically grow Spencer varieties with their naturally thicker stems, and use the following cordon training and layering techniques:
The cordon part of the method:
- Plant a single plant about 5cm from a bamboo cane, ideally fixed to a frame (see video below)
- Dig a hole approximately twice the size of the root ball
- If gardening in very dry sandy soil, place strips of damp newspaper at the bottom of the hole
- Position the sweet pea plug in the hole and cover it with soil up to the first side shoot
- Firm the soil around the roots, without crushing the plug
- Water thoroughly
- As soon as possible, tie the shoots to the support using flexi ties, sweet pea rings, or garden twine
- Once the stems reach about 20cm, select the strongest, sturdiest stem
- Remove the others using clean, sharp secateurs
- Tie the chosen stem onto the cane with flexi ties or garden twine
- Continue tying as it grows, while removing tendrils and secondary stems
The layering part of the method:
- Once the sweet peas reach the tops of their canes, carefully untie them and lay the stems flat: the stems are quite brittle, so don’t rush, and ideally get someone to assist you
- Tie the top 30cm of the stem up a neighbouring cane
- Continue to tie the stems and remove tendrils and side shoots as before
Many thanks to The Dawn Chorus Plot for doing all the hard work for us.