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How to sow runner beans in the UK: depth and canes

Updated: 21 October 2026

You have a packet, and the date on the back is not soil warm enough to germinate. Runner beans are killed by frost, and seed sown into cold, wet ground sits and rots. Sow once the soil is warm and the canes are already in. This page does not rank varieties. The [runner bean seeds comparison](/hub/herb-seeds/runner-bean-seeds) holds the packets, and the buying order is on the [runner bean seeds buying guide](/hub/herb-seeds/runner-bean-seeds/sub/runner-bean-seeds-buying-guide). Peter F. followed the RHS grow guide and the sow windows on these listings, read on 20 October 2026. A qualifying purchase can earn a commission at no extra cost to you.

You have a packet, and the date on the back is not soil warm enough to germinate. Runner beans are killed by frost, and seed sown into cold, wet ground sits and rots.

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Just Seed JustSeed Enorma

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Just Seed JustSeed Moonlight

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Just Seed JustSeed Moonlight
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Mr Fothergill's Mr Fothergill's Mergoles

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Mr Fothergill's Mr Fothergill's Mergoles
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On this page
  1. 1.When to sow in the UK
  2. 2.Depth, pots and planting out
  3. 3.Supports before you sow
  4. 4.Water, picking and the raw-pod rule

When to sow in the UK

There is no single UK date. Indoors, the RHS starts from mid-April into May, above 12°C. Outdoors, wait for soil of about 12°C after the last frost, often mid-May in the south and early June in the north. Late June races the autumn frost. Equator says April to June. Mergoles is indoors April to May and outdoors May to July if the soil is not cold or waterlogged. Polestar, Firestorm and St George say April to July. Streamline, Enorma, Moonlight, Benchmaster and Jackpot print no month, so use those RHS windows. If you have not chosen a variety, use the best runner bean seeds page.

Depth, pots and planting out

The RHS depth is about 5 cm when the packet is silent. Mergoles says 2.5 cm indoors, at 15 to 20°C, and 5 cm outdoors. Follow a stated depth. Do not average the two. One seed to a small pot is enough indoors. Plant out after the last frost, often late May or early June, once the plants are hardened off, beside canes already in the ground. On a patio the final container is not a 9 cm pot. Widths are on the pots page. Listing heights of 25 to 65 cm are not a planting depth.
Just Seed JustSeed Enorma

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Just Seed JustSeed Enorma
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Supports before you sow

Put the canes in before you sow. Climbing runners on the RHS method use canes about 2.5 m tall. On a double row the rows are 45 to 60 cm apart and the canes 15 to 30 cm apart. A wigwam uses five or more canes. Sow two seeds at each cane and thin to one. Pinch the tip when the plant reaches the top. Firestorm's profile runs to about 2.5 to 4 m. Jackpot, the dwarf in this set, needs short sticks and about 30 cm, not that frame. Moonlight and Scarlet Emperor still need the tall canes even if the listing prints a height under 70 cm.

Water, picking and the raw-pod rule

Dry roots are why flowers fall once the plants bloom. In open ground the RHS guide is about 5 to 11 litres per square metre twice a week in dry weather. Check a pot sooner than that. Water the roots, not the flowers. Pick every two or three days at about 20 to 25 cm. A Benchmaster pod can pass 40 cm, which is not the kitchen size. Cook the pods. Raw pods and raw beans are harmful. The Food Standards Agency soak warning is for dried kidney beans, not fresh runner pods. If a child or a pet has eaten raw pods and is unwell, contact NHS 111.

Common questions

When should you sow runner beans indoors in the UK?
From mid-April into May, somewhere above 12°C, if you are following the RHS. One seed to a pot is enough. Mergoles prints its own indoor window of April to May at 15 to 20°C. A packet that says April is not an instruction to sow into a cold porch. Outdoor sowing still waits for soil at about 12°C.
When is outdoor sowing safe in the south and in the north?
When the soil is about 12°C and the last frost has passed. That is often mid-May in the south and early June in the north. June is still a fair outdoor sowing. Late June leaves the crop racing autumn frost. Equator, Mergoles, Polestar, Firestorm and St George print months. Five other packets in this set do not, so the soil temperature is the rule.
How deep do you sow, and what if the packet says 2.5 cm?
The RHS figure is about 5 cm. Mergoles says 2.5 cm indoors and 5 cm outdoors. Follow the packet when it states a depth, and use 5 cm when it does not. Do not average the two into a third number. Outdoor soil that is cold or waterlogged is the problem Mergoles itself tells you to avoid.
How often do you pick, and at what length?
Every two or three days, at about 20 to 25 cm, while the pod is still young. Leaving pods on the plant stops the next flowers. That includes stringless varieties. Benchmaster can exceed 40 cm, which is a reason to pick earlier, not a target length for the kitchen.
Why do the flowers fall off?
Heat and dry roots stop runner beans setting pods. Water the soil in dry weather. The RHS guide for open ground is about 5 to 11 litres per square metre twice a week. Do not mist the flowers. A French-bean cross such as Firestorm or Moonlight is less sulky in a hot summer and still fails if the pot or the row dries out.
Can you eat the pods raw?
No. The RHS states that raw pods and beans are harmful. Cook them. The Food Standards Agency soak advice is for dried kidney beans, not for fresh runner pods, so do not treat a green pod like a dried bean. If a child or a pet has eaten raw pods and is unwell, use NHS 111.

Related pages

Runner bean seeds for pots

Runner bean seeds

Best runner bean seeds UK, by the job on your plot

Runner bean seeds: what to check before you buy one

Runner beans vs French beans: which to sow in the UK

Sources

Public UK sources named below. amazon.co.uk prices, stars and review counts on these eleven listings were read on 20 October 2026. Page updated 21 October 2026.

  1. RHS, How to grow runner beans (retrieved 20 October 2026)
  2. RHS Award of Garden Merit fruit and vegetables (retrieved 20 October 2026)
  3. RHS, Phaseolus coccineus Firestorm (retrieved 20 October 2026)
  4. RHS, Runner beans: failure to set pods (retrieved 20 October 2026)
  5. RHS, What to grow on your allotment (retrieved 20 October 2026)
  6. Seed Marketing Regulations 2011 (retrieved 20 October 2026)
  7. Tozer legumes brochure 2023 UK (retrieved 20 October 2026)
  8. FSA, Home food fact checker (retrieved 20 October 2026)