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Sweet peas are hardy annuals that grow through cool weather and are finished by heat. That single fact sets the whole calendar: the work is front loaded into autumn and winter, and the payoff comes in a burst from late spring through midsummer. A gardener who starts thinking about sweet peas in spring has already given up several weeks of flowering.
The cycle is straightforward. Sow in mid autumn into deep pots and overwinter them cold. Pinch the tips at four leaves. Prepare the ground with plenty of compost or manure while the plants are dormant. Plant out in early spring at the base of a finished support. Tie in for the first two feet. Then pick, every two or three days, from the first flower until heat ends the display, and clear the row.
Two decisions shape the whole year and both are made before spring: when you sow, and how well you prepare the ground. Everything after planting out is water and picking. That is not a criticism of the plant; it is what makes it manageable once it is going.
Expect roughly six months from an autumn sowing to the first flower, and eight to twelve weeks of flowering after that in a cool summer. A late winter sowing shortens the wait to about fourteen weeks but gives a shorter and later display.
| Stage | What to do | What to watch for |
|---|---|---|
| Mid autumn | Sow one inch (2.5 cm) deep in deep pots or root trainers | Mice digging out seed; cover the pots until shoots appear |
| Late autumn | Pinch each seedling at three or four true leaves | Drawn pale seedlings mean they are too warm; move them colder |
| Winter | Keep cold, bright and airy; water sparingly | Waterlogged compost rotting the base; ventilate the frame on mild days |
| Late winter | Dig manure or compost into the row; build the support | Side shoots breaking from the base of each plant |
| Early spring | Harden off, then plant out 6 to 9 inches (15 to 23 cm) apart | Slugs on planting night; protect from the first day |
| Mid spring | Tie the first two feet (60 cm) in, spread shoots sideways | Shoots braiding up one strand instead of covering the support |
| Late spring | First flowers; start half strength potassium feed | Bud drop from cold nights; it passes on its own |
| Early summer | Pick every two or three days; remove every pod | Fat green pods behind faded flowers; the display stops if they fill |
| Midsummer | Water deeply, mulch, keep picking hard | Short bleached stems and fading scent mean heat is arriving |
| Late summer | Clear the row once flowering ends; prepare ground for autumn | Powdery mildew on the lower growth; do not compost it |
Autumn and winter: the part that decides the season
Sow in mid autumn while six to eight weeks of mild weather remain. Use deep containers, one inch (2.5 cm) deep, and gritty all-purpose potting mix. The plant you are aiming for by the time hard cold arrives is short, sturdy, with three or four leaves and a pot full of root. That plant will outperform anything sown in spring by a wide margin.
Pinch the tip out as soon as the fourth leaf is open. Waiting until the plants look substantial defeats the purpose; the earlier the pinch, the more shoots break from the base and the better the plant is shaped for the whole season.
Through winter the job is almost entirely restraint. Keep the pots cold, bright and ventilated, water only when the compost has genuinely dried at the surface, and open the cold frame on mild days. More overwintered sweet peas are lost to warmth, damp and closed air than to frost.
Use the winter to prepare the ground. A trench a spade deep filled with well rotted manure or compost, dug in late autumn or early winter and left to settle, is the traditional preparation and it works. Sweet peas are hungry and root deeply, and ground prepared now saves feeding all summer.
- Sow deep and keep cold One inch (2.5 cm) deep in root trainers or deep pots, overwintered in a cold frame or against a sheltered wall. Cover against mice until the shoots are up, and ventilate whenever the weather is mild.
- Pinch at three or four leaves Take the growing tip out just above a leaf joint. This is what converts one thin leader into three or four strong basal shoots, and it is the difference between a thin display and a full one.
- Prepare the row before spring Dig in plenty of well rotted manure or compost, a spade deep, in late autumn or winter. Build the support to its full six to eight feet (1.8 to 2.4 m) before anything is planted.
- Plant out early and protect from slugs Harden off for a fortnight and plant into cool soil in early spring, at the depth they grew, without disturbing the root column. Slug protection goes down the same day, not after damage appears.
Spring and summer: tie in, then pick and pick again
From planting out until the plants are two feet (60 cm) tall, the weekly job is tying in. Stand each shoot against the netting or cane, secure it loosely with soft twine, and spread the shoots sideways so the support fills evenly. After that the tendrils take over and the handling stops.
From the first flower, the only real job is picking, and it has to be done every two or three days without exception. Cut whole stems at the joint, take fading flowers as well as fresh ones, and remove every pod you find. A week of neglect in early summer costs the rest of the season, which is a harsher penalty than most garden plants impose.
Water deeply once or twice a week, more in containers, and mulch the row once the soil warms. Start a half strength high potassium feed when the first buds show and repeat every ten to fourteen days. Do not feed nitrogen; it gives leaf at the expense of flowers.
When heat arrives, the stems shorten, colors pale and scent fades. Water and mulch delay this and hard picking extends it, but nothing prevents it. When the row is producing only short two flower stems and the lower leaves are going gray with mildew, it is finished.
If you go away in early summer, strip every flower, bud and pod from the row before you leave. A plant that fills its pods in your absence does not restart. A stripped plant is flowering again within a week or two of your return.
Clearing up, seed, and setting up next year
Clear the row promptly once flowering ends. Pull the plants, strip them off the netting, and put mildewed material in the rubbish rather than the compost pile. Leaving exhausted plants in place through late summer gains nothing and leaves a reservoir of mildew and aphids beside whatever you plant next.
Saving seed is possible but it is a deliberate decision, not something to do by default. Leave pods on a small number of plants at the very end of the season, once you have accepted that the flowering is over, and collect them when the pods are brown and papery but before they split. Never leave pods on plants you still want flowers from, because that is precisely what stops them.
Sweet pea seeds and pods are poisonous. Store collected seed labeled, dry, cool and well away from any vegetable seed, and keep it out of reach of children who may recognize it as a pea.
Finish the year with the notes. Sowing date, pinching date, planting out date, first flower, stem counts through the season, and the date it stopped. Add a line on what you fed and where the row was. That short record turns next autumn's sowing from guesswork into a decision, and it is the reason the second year of growing sweet peas is so much better than the first.