Why climbing beans are perfect for a small balcony

Climbing beans are one of the most rewarding crops for a balcony. They grow upwards, not outwards, so a narrow space can produce a surprisingly generous harvest. In the UK, both runner beans and French climbing beans thrive in containers, provided they have deep roots and a sturdy support. The warm, sheltered microclimate of a balcony often suits them better than an exposed allotment. Choose varieties such as 'Scarlet Emperor' for classic red flowers, 'Blue Lake' for stringless French beans, or 'Cobra' for heavy yields. You will get fresh pods from July to September, and the flowers are a joy in themselves.

Choosing the right support: wigwams, trellis and string lines

The support you choose depends on your balcony's shape and how much wall space you have. All three methods work well, but each has its own practicalities.

• Bamboo wigwams are ideal for a corner or a large pot. Push six to eight canes, each around 2 metres tall, into the compost around the edge of the pot. Bring the tops together and tie them firmly with garden twine. For extra stability, tie the wigwam to a balcony rail or wall bracket. Plant one bean at the base of each cane.
• Trellis against a wall makes excellent use of vertical space. Fix a wooden or metal trellis to the wall using hooks or brackets, leaving a small gap for air circulation. You can also lean a freestanding trellis against the wall and secure it at the top. Beans will twine through the gaps, and the wall releases warmth at night.
• String lines are the simplest and cheapest option. Screw small hooks into the wall or use a tensioned wire, then tie vertical strings from the top to the pot below. Space them 20–25cm apart. Beans grip the string readily, and you can adjust the tension as they grow. This method is perfect for narrow balconies where a wigwam would block the view.

Deep pots and the right compost for healthy roots

Climbing beans have extensive root systems, so shallow containers will lead to weak plants and poor cropping. Choose pots that are at least 30cm deep, ideally 45cm, and 30–40cm in diameter. A volume of 30–40 litres is ideal for a wigwam of six beans. If you are using string lines, a rectangular trough of similar depth works well.

Good drainage is essential. Place crocks or broken polystyrene at the bottom of the pot, and make sure there are drainage holes. Fill with a peat-free multipurpose compost mixed with a few handfuls of garden compost or well-rotted manure. Add a slow-release fertiliser at planting time. During the growing season, water consistently — little and often — and never let the compost dry out completely. A layer of mulch, such as grass clippings or bark chippings, will help retain moisture on hot days.

Planting, training and pinching out

Sow seeds indoors in April or May, one per small pot, and harden them off before planting out after the last frost. In most UK areas, this is late May or early June. Plant them so that the base of the stem is slightly deeper than it was in the seed tray. Water well after planting.

As the plants grow, guide the shoots onto their supports. They will twine naturally, but a little help in the first week or two pays off. Once a stem reaches the top of its cane, trellis or string, pinch out the growing tip. This is the single most useful pruning trick for container beans. Pinching out encourages side shoots, which carry more flowers and pods, and it stops the plant from becoming top-heavy and tangled. Repeat the pinch if new leaders appear. Remove any yellowing leaves near the base to improve airflow.

Ongoing care: water, feed, pests and harvest

From flowering onwards, beans need plenty of water. On a sunny balcony, you may need to water twice a day. Feed with a liquid tomato fertiliser every fortnight once the first flowers appear. This supports pod development and extends the cropping season.

Aphids, especially blackfly, can be a nuisance. Check the growing tips regularly and remove any colonies with a strong jet of water or by squashing them. Ladybirds and lacewings will help if you avoid sprays. Slugs and snails may climb into pots; a copper tape barrier around the rim works well. Wind can snap brittle stems, so if your balcony is exposed, tie a piece of fleece or windbreak netting to the rail — but leave gaps for bees to reach the flowers.

Harvest runner beans when they are 15–20cm long and French beans when they are pencil-thick, before the pods become stringy. Pick every few days to keep the plants productive. At the end of the season, cut the plants at the base and add the tops to the compost heap, leaving the roots to release nitrogen into the compost for your next crop.