Runner beans are the classic British summer bean: scarlet flowers on a wall of green, and long pods you pick by the armful from late July until the first frost. They are easy to grow from seed, but they have a few needs of their own. They want warm soil to germinate, tall and strong supports, and above all steady water at the roots when they flower. This guide covers how to grow runner beans from seed (Phaseolus coccineus): when and how to sow, how to build supports, how to get the flowers to set pods, and how to keep the harvest coming. It also covers two jobs you can do this autumn: digging a bean trench, and saving the roots for next year.
- Sow Late April–May indoors · late May–early July outdoors
- Spacing 15–20 cm apart · canes or poles 2.4 m tall
- Harvest Late July until the first frost · pick every 2–3 days
- Site Sun, shelter from wind · deep, moisture-holding soil
What makes a runner bean different
Runner beans are not simply tall French beans. They are a separate species from the cool mountains of Mexico and Central America. In the wild they are perennial, with a fleshy, tuber-like root that regrows each spring. In British gardens we grow them as annuals, because the frost kills the top growth and usually the roots too. Three things follow from that origin. They like cool, damp summers better than hot, dry ones. They need insects to pollinate the flowers. And their seed leaves stay below ground when they germinate, so the first thing you see is a shoot, not a pair of round leaves. Our French bean guide explains how the two species compare in the garden and in the kitchen.
When to sow runner beans
Runner beans are tender. Seed rots in cold, wet soil, and frost kills young plants outright. Two timings work:
- Indoors, late April to mid-May. Sow one bean 5 cm deep in a deep 9 cm pot or root trainer. Keep them on a windowsill or in a greenhouse at 12–20 °C, and plant out after the last frost, usually late May or early June. This gives the earliest crop and keeps young plants safe from slugs.
- Outdoors, late May to early July. Sow two beans 5 cm deep at the foot of each cane once the soil has warmed to about 12 °C. Thin to the stronger seedling. A sowing in late June or early July crops from September until the frost, when early plants are flagging.
Do not soak the seed for more than a few hours, if at all. Beans that take up water too quickly can split and rot. Harden off pot-grown plants for a week before planting, as in our hardening-off guide. Our vegetable sowing calendar shows where runners fit among your other sowings.
Supports: build them before you plant
A healthy runner bean climbs 2.5–3 m in a season, and a row in full leaf catches the wind like a sail. Put the supports up before the plants go in. Use 2.4 m canes or hazel poles pushed 30 cm into the ground. You can set them in a double row, 60 cm apart, crossed and tied to a ridge cane along the top. Or you can tie them into a wigwam of six to eight canes. Double rows are sturdier and give more beans. Wigwams take less space and suit a raised bed or a large pot. Our guide to plant supports and trellising has more designs. Tie each young plant loosely to its cane, and it will twine its own way up from there.
How to grow runner beans, step by step
- Prepare the ground (autumn or early spring) Dig a trench a spade deep along the row and fill it with compost or kitchen scraps. See the bean trench below.
- Put up the supports (May) Canes 2.4 m long, 15–20 cm apart, firmly tied at the top.
- Sow or plant out (late May–June) One plant per cane, after the last frost. Protect from slugs for the first fortnight.
- Start them climbing Guide the first shoot round the cane and tie it in loosely. After that they twine on their own.
- Pinch out the tops When the plants reach the top of the canes, pinch out the growing tip. This pushes energy into side shoots and flowers.
- Water hard from the first flower About 5–10 litres per square metre, twice a week in dry spells, then mulch to keep the moisture in.
- Pick young and often (late July–frost) Pick pods at 15–20 cm, before the beans bulge inside, every two to three days.
Why runner bean flowers drop without setting pods
This is the most common runner bean problem. The plants grow well and flower freely, but the flowers fall and no pods form. The usual cause is dry roots while the plants are flowering, often made worse by hot days and warm nights. Water the soil deeply, not the leaves, and lay a thick mulch over the root zone. Our watering guide explains why a deep soak twice a week beats a daily sprinkle. Wind and a lack of bees also play a part. Shelter helps, and so does growing flowers for bees nearby. In hot summers, white-flowered and bicoloured varieties often set better than pure scarlet ones.
Scarlet-flowered runners
The traditional look, with large seed and long pods.
- Long, straight pods with plenty of flavour, such as 'Streamline'
- Large-seeded scarlet types also dry well for winter
- Most reliable in a cool, damp summer
White and bicoloured runners
Often set pods more easily when the weather turns hot.
- 'Emergo': white flowers, white seed, fleshy pods (also organic)
- 'Painted Lady': red-and-white heirloom flowers
- Pretty enough to grow over an arch or a fence
An autumn job: dig a bean trench
Runner beans root deeply and need a constant supply of moisture, so the traditional preparation starts in autumn. Dig a trench about 30 cm deep and 60 cm wide where next year's row will go. Through the winter, fill it with vegetable peelings, spent plants and torn newspaper. Then backfill the soil in early spring. By May the trench is a damp, open sponge that the roots can follow down. A thick layer of garden compost does a similar job if you prefer not to dig; see composting for beginners. Grow runners where no legumes grew the previous year, and follow them with cabbages or kale, as in our crop rotation plan. After harvest, cut the stems at soil level and leave the roots in the ground to break down.
Can you overwinter runner bean roots?
Yes, because the species is perennial. Once the first frost blackens the leaves, lift the fleshy roots, cut the stems back to 5 cm and store the roots in barely damp compost somewhere cool and frost-free. It is the same method we use for dahlias in overwintering tender plants. Pot them up in April and plant out after the frosts, and they will flower a few weeks earlier than seed-sown plants. In mild, well-drained gardens, a deep mulch over roots left in the ground sometimes works too. Plants grown from saved roots tend to lose vigour after a year or two, though, and fresh seed is cheap and reliable. Treat it as an experiment rather than a replacement.
Common mistakes
- Sowing too early: cold, wet soil rots the seed. Wait for warm soil or start them in pots.
- Flimsy supports: a laden row can flatten short canes in the first August gale.
- Watering little and often: pods set when the soil is moist deep down, not just on the surface.
- Leaving pods on the plant: once seeds start to ripen, the plant stops flowering. Pick everything, even the ones that got away.
- Forgetting the slugs: a single night can take every young shoot in a newly planted row.
Frequently asked questions
How many runner bean plants do I need?
For a family of four, a wigwam of eight plants or a 2 m double row is usually plenty. Picked regularly, each plant crops for two months or more. If you have a glut, slice the beans, blanch them for two minutes and freeze them.
Can I grow runner beans in a pot?
Yes. Use a container of at least 40 litres with a wigwam of five canes, and water every day in summer. Our container gardening guide covers compost and feeding.
Can I save my own runner bean seed?
Yes. Leave a few pods on the plant until they turn dry and papery, then shell the beans and dry them fully. Bees cross different runner varieties, so grow only one variety if you want it to come true. Our guide to drying beans covers drying and cooking, and seed saving covers storage.
Do runner beans and French beans cross?
Very rarely. They are separate species, so you can grow them side by side and still save seed from both.
A single row of runner beans gives more food per square metre than almost anything else in the vegetable garden, and it looks good while it does. If you are new to vegetables, start with our beginner's guide to growing vegetables from seed. Browse the Phaseolus coccineus, climbing beans and legumes collections, or all our seeds, and keep our growing guides to hand.
