When to Plant Sweet Peas | Ashridge Trees

Contents

1 When Should You Plant Sweet Peas in the UK?
- 1.1 Related guides
2 What Are the Two Main Planting Windows for Sweet Peas?
3 How Do You Sow Sweet Peas in Autumn?
4 When Is the Best Time to Sow Sweet Peas in Spring?
5 When Can You Plant Sweet Peas Out in the Garden?
6 When Do You Plant Out Sweet Pea Plug Plants?
7 How Late Can You Plant Sweet Peas and Still Get Flowers?
8 Can You Sow Sweet Peas Directly Outdoors?
9 When Should You Prepare the Soil for Sweet Peas?
10 Which Varieties Are Best for Autumn and Spring Planting?
11 What Are the Most Common Timing Mistakes With Sweet Peas?
12 Frequently Asked Questions
13 Related Products
14 Related Articles

When Should You Plant Sweet Peas in the UK?

Sweet peas can be sown from October through to April in the UK, giving you two main planting windows: an autumn sow for the earliest, strongest plants, and a spring sow for a straightforward season without the need for overwintering. The exact timing that suits you best depends on your climate, soil, and whether you are starting from seed or planting out young plug plants. Get it right and you will have blooms from late May; leave it too late and flowering is pushed into July or beyond.

Related guides

What Are the Two Main Planting Windows for Sweet Peas?

There is an autumn window (October–November) and a spring window (February–April), and both produce excellent results with slightly different advantages.

Autumn-sown sweet peas are started under glass in October or early November. The seedlings are grown on through winter in a cold frame or unheated greenhouse, developing a robust root system before the cold really bites. By the time spring arrives they are ahead of any spring-sown rivals by four to six weeks, which typically means flowers from late May rather than mid-June.

Spring sowing is simpler and carries less risk of losses to cold, damp, or mice over winter. Seeds sown indoors in late February or March under cover germinate quickly in the warmth, grow fast, and are ready to harden off and plant out in April or May. Flowering usually begins in June and continues until the plants exhaust themselves in late summer.

Method	Sow / Plant	First Flowers	Best For
Autumn sow (under glass)	Oct–Nov	Late May–early June	Exhibitors, those with cold frames
Spring sow (indoors)	Feb–Mar	Mid-June	Most gardeners, easier management
Direct sow (outdoors)	Mar–Apr	Late June–July	Mild areas, minimal fuss
Plug plants (pot on or plant out)	Delivered Mar–May	June–early July	No-fuss, guaranteed varieties

How Do You Sow Sweet Peas in Autumn?

Sow autumn sweet peas between mid-October and early November, before short days and cold slow germination too much, but late enough that seedlings do not grow too tall and soft before winter.

Use deep root trainers or individual 9 cm pots filled with a good seed compost — sweet peas form a tap root very quickly and resent being cramped or disturbed. Soak hard-coated seeds overnight in water, or nick the coat with a nail file on the opposite side to the eye, to speed germination. Sow one or two seeds per cell at a depth of about 2 cm. Place in a cold frame or unheated greenhouse; a temperature of 10–15 °C is ideal for germination, which takes 7–14 days.

Once the seedlings reach about 10 cm, pinch out the growing tip to encourage bushy side shoots rather than a single weak stem. Keep watering sparingly through winter to avoid rot, and protect from hard frost with fleece. In mild spells, ventilate the frame freely. By late February the plants will be stocky and dark green, ready to grow away strongly as days lengthen.

When Is the Best Time to Sow Sweet Peas in Spring?

Late February to mid-March is the sweet spot for spring sowing under cover in most parts of the UK; a heated propagator is helpful but not essential if you have a warm windowsill.

Sow as for autumn, using deep pots or root trainers. On a warm windowsill (around 15–18 °C) seeds will germinate in five to ten days. Move seedlings to a cooler, bright position as soon as they emerge — a cool greenhouse or conservatory at 10–12 °C is perfect — to keep growth compact and prevent leggy, drawn stems. Pinch out tips at two to three pairs of leaves, just as you would with autumn seedlings.

From early April, begin hardening the plants off by placing them outside during the day and bringing them in at night. After a fortnight of acclimatisation they can be planted out once the risk of hard frost has passed — usually mid to late April in the South and early May in the North and Scotland.

When Can You Plant Sweet Peas Out in the Garden?

Sweet peas can be planted into their final outdoor position once nighttime temperatures stay reliably above about −3 °C and the soil is workable — typically April in most of England and Wales, and May in Scotland and Northern Ireland.

Sweet peas are hardier than many annual flowers and can withstand a light frost once acclimatised, but a prolonged freeze below −5 °C will damage young plants. Timing also varies with your soil: heavy clay that stays cold and wet into May is less welcoming than a light, free-draining loam that warms quickly. If in doubt, plant into large pots first and move outdoors as a unit once conditions improve.

Region	Earliest Safe Planting Date	Note
South-West England & coastal Wales	Late March–early April	Mild winters; autumn sowings thrive
South & Central England	Mid-April	Standard benchmark for most guides
Midlands & North of England	Late April–early May	Watch for late frosts into May
Scotland & Northern Ireland	Early to mid-May	Spring sowing usually more reliable

When Do You Plant Out Sweet Pea Plug Plants?

Sweet pea plug plants from Ashridge are despatched in spring — usually from March through to May — and should be potted on into 9 cm pots as soon as they arrive, then hardened off and planted out once frost risk is low.

Plug plants arrive as rooted young plants, already past the germination and pricking-out stages. When they arrive, water them gently, pot them on into individual pots of peat-free multipurpose compost, and place them in a cold frame or cool greenhouse. Give them a week or two to settle and grow on before beginning the hardening-off process described above. This approach removes a great deal of the uncertainty around timing and seed storage, and gives you exactly the variety you want — whether that is the legendary scent of Anniversary, the deep navy of Blue Velvet, or the striking near-black of Almost Black.

How Late Can You Plant Sweet Peas and Still Get Flowers?

Sweet peas sown outdoors as late as early April can still produce a good flush of flowers before the summer heat triggers their decline, but anything planted after mid-May will give a disappointingly short season.

Sweet peas flower from the base of the plant upward and then stop once temperatures consistently exceed around 25–27 °C for extended periods, which in the UK typically happens in July or August. A plant put in the ground in May has far less time to build stems and root mass before the heat arrives than one planted in April. If you have missed the optimal window, choose fast-maturing varieties, keep plants well watered, pick flowers every two to three days to delay seed set, and accept that the season may run from early July to August rather than from June onwards.

Can You Sow Sweet Peas Directly Outdoors?

Yes — you can sow sweet peas directly into the ground in March and April once the soil has reached at least 10 °C, though indoor-raised plants almost always perform better and flower earlier.

Direct sowing works best on well-drained, fertile soil in a sheltered, sunny spot. Sow seeds 2–3 cm deep and about 10 cm apart, thinning to 20–25 cm once they have two or three pairs of leaves. The main risk is slug damage to the emerging shoots; scatter organic slug pellets or use wool mulch around the emerging seedlings. Mice are also fond of sweet pea seeds, particularly in autumn — if this is a problem, sow in pots under cover and plant out as seedlings.

When Should You Prepare the Soil for Sweet Peas?

Prepare the planting site the autumn before if at all possible — or at least four to six weeks before planting — so that organic matter breaks down and the soil settles before the plants go in.

Sweet peas are deep-rooted and hungry plants that reward thorough ground preparation. Dig a trench at least 30 cm deep (some exhibitors dig 60 cm), incorporating well-rotted garden compost or manure at every spade depth. This not only feeds the plants but dramatically improves moisture retention, which is critical in dry summers. If you are preparing in spring rather than autumn, use bagged organic compost and allow it at least a month to integrate before planting. A handful of bonemeal forked in at planting time gives a gentle, long-release phosphate boost to encourage strong root development.

Which Varieties Are Best for Autumn and Spring Planting?

Almost all heritage and Spencer varieties suit both planting windows equally well; variety choice is better guided by colour, scent, and stem length than by season.

That said, some varieties have particularly robust constitutions that help them stand up to the variable conditions of an autumn or early spring planting.

Variety	Colour	Scent	Notes
Anniversary	Blush pink	Exceptional	Long stems, superb cut flower
Albutt Blue	Pale blue/mauve	Strong	Classic Spencer, highly regarded
Black Knight	Deep maroon	Good	Old-fashioned type, rich colour
Flora Norton	Mid blue	Excellent	Heritage variety, very fragrant
Charlie’s Angel	Pale lavender	Strong	Reliable, vigorous grower
Almost Black	Very deep maroon	Good	Striking, dramatic flower
Bramdean	Soft lavender pink	Excellent	Cottage garden favourite
Ballerina Blue	Rich blue	Good	Bold colour, good vigour

For a fuller list of all available varieties including Bobby’s Girl, Erewhon, America, and Bristol, visit the Ashridge sweet peas collection.

What Are the Most Common Timing Mistakes With Sweet Peas?

The three most frequent errors are sowing too late in spring, planting out before hardening off, and leaving autumn seedlings to grow too tall and soft before winter.

Mistake	Result	Solution
Sowing spring seeds too late (after April)	Short flowering season, plants set seed before performing well	Aim for Feb–March indoors; use plug plants if you have missed the window
Planting out without hardening off	Wilting, leaf scorch, check in growth	Two weeks of acclimatisation outdoors in daytime before final planting
Autumn seedlings grown too warm	Tall, soft, frost-tender plants that collapse over winter	Keep in cold frame or unheated greenhouse, not a warm house
Sowing autumn seeds too early (September)	Plants become large and soft before winter, suffer more damage	Stick to October–early November
Not pinching out growing tips	Single-stemmed, weak plants with fewer flowers	Pinch out at 10–15 cm to promote bushy side shoots

Frequently Asked Questions

Can I sow sweet peas in January?

January sowing is possible on a heated propagator, but without long days seedlings quickly become tall and drawn. It is better to wait until late February for indoor spring sowings to get sturdy, compact plants.

Is it too late to plant sweet peas in May?

May sowings or plantings are late but not hopeless in most UK regions. You will get flowers from July, though the season will be shorter. Use plug plants from the Ashridge sweet peas range to save time.

Do sweet peas need to be soaked before sowing?

Soaking seeds overnight in tepid water softens the seed coat and speeds germination, particularly on harder-coated varieties. It is helpful but not strictly essential — nicking with a file works equally well.

How long do sweet peas take to germinate?

At 15–18 °C, most sweet pea seeds germinate in 7–14 days. Cooler conditions in an autumn cold frame may slow this to three weeks. Pre-soaking or nicking the seed coat reliably speeds the process.

When should I pinch out sweet pea seedlings?

Pinch out the growing tip when the plant has two to three pairs of leaves, leaving the lower side shoots to develop. This produces a bushier plant with far more flowering stems than an unpinched seedling.

Can I plant sweet peas straight from the plug without hardening off?

No — plants grown under cover need two weeks of gradual exposure to outdoor conditions before planting out. Skipping this causes wilting and can set plants back by several weeks.

What temperature do sweet peas need to germinate?

Sweet peas germinate best between 13 °C and 18 °C. Higher temperatures can inhibit germination. A cool windowsill or cold greenhouse in early spring provides near-ideal conditions.

How far apart should I plant sweet peas?

Plant sweet peas 20–25 cm apart along a support structure. For a double row, leave 45 cm between rows. This gives adequate air circulation and reduces the risk of powdery mildew later in the season.

Should I water sweet peas in after planting?

Yes — water in thoroughly at planting and keep the soil consistently moist while plants establish. Once growing strongly, sweet peas need regular watering, especially in dry spells, to maintain flowering and prevent mildew.

Can I grow sweet peas in pots, and does timing differ?

Sweet peas grow well in deep containers of at least 30–40 cm depth. Timing for pot-grown plants follows the same principles as open-ground planting. See our guide on growing sweet peas in pots for full details.

Why do my autumn-sown sweet peas die over winter?

The most common causes are overwatering (leading to root rot), growing them too warm so they become soft and frost-tender, or neglecting to protect them during hard spells below −5 °C. Ventilate freely in mild weather and water sparingly.

What is the latest month I can buy sweet pea plug plants?

Ashridge typically despatches sweet pea plug plants from March through to May. Ordering early ensures availability of the most popular varieties such as Anniversary and Brook Hall.