Annual climber
How to grow sweet peas
Lathyrus odoratus
Sweet peas are hardy annual climbers sown in October and November in a cold frame, or in February and March, then planted out in April in full sun. They need a deep, rich, moist root run and a support about 2 m tall. Two habits decide how long they flower: never let the roots dry out, and pick every bloom before it can set a pod. Done well, they flower from June into September.
- Hardiness
- Hardy annual, autumn sowings overwinter in a cold frame
- Position
- Full sun
- Soil
- Deep, rich, moisture-retentive
- Ideal pH
- 6.5 to 7.5
- Water
- High, never let them dry at the root
- Feeding
- Moderate feeder
Sowing and planting sweet peas
WhenSow Oct to Nov or Feb to Mar; plant out Apr; flowers Jun to Sep
Starting off
Sow Oct to Nov in a cold frame or Feb to Mar at 15 °C, two seeds per 7 cm pot or root trainer, 1 cm deep; germination takes 10 to 14 days, and soaking hard seed overnight is optional. Pinch tips at 10 cm to encourage side shoots and plant out in Apr after a fortnight's hardening off.
Spacing and planting
Plant 20 to 30 cm apart along a wigwam, netting or 2 m canes; for cordon cut flowers set one plant per cane 20 cm apart in rows 1.2 m apart. Fine in a deep 30 to 40 cm pot with a tripod if never allowed to dry out.
Varieties worth growing
- 'Cupani'
- The original 17th century type: small maroon and violet flowers with the strongest scent of any. Short stems, but tougher in heat than the modern kinds.
- 'Painted Lady'
- Old-fashioned pink and white bicolour, very fragrant and early. A good choice for a wigwam in a border where scent matters more than stem length.
- 'Gwendoline'
- Spencer type with large, frilled pink flowers on long stems. A standard for cutting and for cordon growing, and still well scented.
- 'Charlie's Angel'
- Pale blue Spencer with four or more flowers to a stem and good scent. Reliable and vigorous on a row of canes.
- 'Pink Cupid'
- Dwarf, trailing to about 30 cm with no need for support. The one to grow in a hanging basket or window box.
Sweet peas month by month
Timings are for central England. Allow two weeks later in the north and on cold, heavy soil.
- January
Ventilate autumn-sown plants in the cold frame on mild days. Pinch out any that have reached 10 cm.
- February
Sow at 15 °C, then move seedlings somewhere cool and bright as soon as they are up. Dig compost into the planting site.
- March
Last sowings. Pinch tips at 10 cm. Put up supports. Start hardening off autumn-sown plants.
- April
Plant out 20 to 30 cm apart. Tie in the first shoots and protect from slugs.
- May
Tie in weekly. Water in dry spells. Mulch once the soil is moist.
- June
First flowers. Pick every few days. Begin the potash feed at first bud.
- July
Pick, pick, pick. Remove every pod. Water deeply twice a week in dry weather.
- August
Stems shorten in heat. Keep watering, feeding and picking. Watch for mildew.
- September
Cut finished plants off at ground level and leave the roots in the soil.
- October
Sow in deep pots or root trainers in a cold frame. Protect from mice.
- November
Finish autumn sowing. Keep the frame open except in hard frost or heavy rain.
- December
Nothing to do beyond ventilating the frame on mild days.
Feeding sweet peas
A legume that fixes its own nitrogen, so it wants organic matter and moisture at the root, phosphorus and potash, and no nitrogen feed at all.
Fixes its own nitrogen, so go easy on N, a potassium-leaning feed once flowering keeps blooms coming on rich, moisture-holding soil.
Feeding plan
Autumn or March, before planting
Garden compost
A bucketful per metre of row, or two per wigwam, dug in a spade deep. This matters more than any fertiliser.
April, at planting
100 g/m², the maintenance end of the label. A row 30 cm wide takes 30 g per metre; a wigwam 60 cm across (about 0.3 m²) takes 30 g.
First bud to late August, every 2 weeks
Potassium Rich Fertiliser 11% K
0.5 to 1 g per litre of water as a drench: 4.5 to 9 g in a 9 litre can, one can per metre of row. The label interval is 2 to 4 weeks, so do not feed more often than fortnightly.
Pots, first bud onwards
Potassium Rich Fertiliser 11% K
The same 0.5 to 1 g per litre every 2 weeks, in place of a plain watering. No nitrogen feed.
Signs to watch
Buds drop before opening
A sudden cold night or dry roots, not a nutrient fault
Water consistently and mulch
Pale leaves and weak growth in a pot
Nitrogen washed out
A dilute seaweed feed, never strong nitrogen
Short stems and faded colour in Jul
Potash short and heat stress
A high-potash liquid feed weekly
Pests, diseases and problems
Seeds vanish from pots, or seedlings are bitten off, in a cold frame over winter
Mice, which find pea seed by smell
Cover pots with fine wire mesh or a sheet of glass until seedlings are 5 cm tall, and set traps in the frame.
Young plants grazed to stumps after planting out in April
Slugs and snails
Plant out sturdy, hardened-off plants, not soft ones; torch patrols for the first three weeks, and nematodes once the soil is above 5 °C.
Green insects packed on shoot tips and buds, growth distorted
Aphids, which also carry virus
Squash or wash off with water every few days. Check autumn-sown plants in the frame before planting.
Leaves mottled or streaked yellow, flowers streaked with a darker colour, plants stunted
Virus spread by aphids
Pull up and bin affected plants promptly. Do not save seed from them.
White powder over leaves and stems from late July
Powdery mildew, on plants stressed by dry roots at the end of the season
Water deeply, mulch, and keep picking. Once it is severe in late August the plants are finished: pull them.
Small black beetles crawling out of cut flowers indoors
Pollen beetles, harmless to the plant
Stand the picked bunch in a dark shed or garage with the door ajar for an hour; the beetles leave for the light.
Pruning
Pruning and care
Tie in weekly, as tendrils alone give a tangle; for cordons remove tendrils and side shoots and tie the single stem every 15 cm. Cut every bloom every few days from Jun and remove any pod at once, as seed set stops flowering within weeks. Pull plants in Sep; autumn-sown plants in a cold frame need only ventilation on mild days, no heat.
Good to knowPick or deadhead constantly, let pods set and flowering stops. Give tall supports.
Growing sweet peas in pots
Use a pot at least 40 cm deep and wide, since sweet peas root deeply and a shallow pot dries in hours. Fill with peat-free multipurpose mixed with a third of loam-based compost, set five or six plants round a 1.8 m cane tripod, and water daily from June, twice in hot weather. Dwarf types such as 'Pink Cupid' need no support and suit baskets. Pot-grown plants finish earlier than those in the ground, usually by early August, because the roots get hot.
Sweet peas: common questions
Should I soak sweet pea seeds before sowing?
It is not needed for most varieties. Fresh seed germinates in 10 to 14 days in moist compost without soaking, and soaked seed is more likely to rot in a cold frame. If seed is old or very hard, soak overnight and sow only those that have swollen.
Why have my sweet peas stopped flowering?
Almost always because seed pods have been allowed to form. Once a plant sets seed it stops making flowers within weeks, so remove every pod and pick all open blooms every two or three days. Dry roots and hot weather in late July are the other cause: water deeply and mulch.
Is it better to sow sweet peas in autumn or spring?
Autumn sowing gives stronger plants that flower two to three weeks earlier and for longer, provided you have a cold frame or unheated greenhouse to overwinter them. Spring sowing in February or March is simpler, avoids mice and winter losses, and still flowers well from late June.
Sources
Growing information on this page was checked against these references in November 2026. Feeding rates are Dr Forest label rates.