Originating from South-East Asia, soya beans (Glycine max) are tender plants that need full sun, heat and plenty of moisture to produce a good crop in the UK. But as our climate warms and new, more resilient varieties are introduced, they are becoming a more viable option.
when the beans are the size of garden peas, still green and immature, for cooking and eating fresh in salads, stir-fries and many other dishes. These are usually known as edamame beans
when the pods are fully ripe and dry – the mature soya beans inside can stored for use in stews and other hearty winter dishes
The plants can be grown from seed sown indoors or outside. They form bushy plants about 60cm (2ft) tall, depending on the variety, and don’t usually need supports. The beans are a good source of protein and fibre, but they must always be cooked before eating, to get rid of any natural toxins.
Month by Month
Soya beans generally need a long, hot summer, ideally 20–30°C (68–86°F), although some newer varieties can cope in cooler conditions. Make sure you choose a variety suitable for your local climate, otherwise results may be disappointing.
Most varieties sold in the UK grow to around 60cm (2ft) tall and are self-supporting, although some taller varieties may be available and will require supports.
Soya bean seeds are often sold as edamame beans, which is the name given to the immature green beans, but these can be harvested as mature dried beans too.
What and where to buy
Seeds are available in garden centres and from online seed suppliers. Young plug plants may also be available in late spring and early summer, from similar sources.
Preparing the Ground
Choose a warm, sunny growing site. Weed thoroughly, then add lots of well-rotted manure or garden compost – at least two buckets per square metre/yard. This should ideally be done a few weeks ahead of sowing or planting out, to allow time for the ground to settle.
It’s also a good idea to warm the soil before sowing, to aid germination.
Soya beans can be sown indoors or outdoors, in May or June. Plants are tender, so keep them indoors until the ground has warmed up in late spring or early summer. Sowing indoors lets you get a head start, and keeps the seedlings out of reach of slugs and snails until they are larger and more robust. Give these plants your warmest, sunniest spot, for the best chance of a good crop.
Sow soya beans in small pots or modular trays filled with seed compost, setting them 5cm (2in) deep. Place in a propagator, or cover with a clear polythene bag, and keep at a temperature of 18–20°C (64–68°F). .
Once the seedlings appear, remove from the propagator or uncover, then keep in warm, bright location. Move the seedlings into larger pots when roots appear through the drainage holes.
In late May or early June harden off the young soya plants to acclimatise them to outdoor conditions. Then plant into their final site after all risk of frost has passed – see Planting, below.
You can sow soya beans outdoors once the soil has warmed to at least 15°C (60°F) in late spring or early summer. Prepare the ground as detailed above.
Sow the seeds 5cm (2in) deep, 15cm (6in) apart, in rows 45cm (18in) apart, then cover with fleece or cloches.
Protect the seedlings from slugs and snails.
Wait until early summer, when temperatures are around 15°C (60°F), before planting indoor-raised soya plants or young bought plants outside. Harden off for a couple of weeks to avoid a check in growth.
Water the young soya plants well, both before and after planting, and space them 15cm (6in) apart, with 45cm (18in) between rows.
After watering in, spread a thick layer of garden compost over the surrounding soil to help retain moisture. Then cover the plants with fleece or cloches to keep them warm while they settle in.
Soya plants need protection from slugs and snails when young, and regular watering. Most varieties grow to about 60cm (2ft) tall and are self-supporting, but taller varieties may be available and those plants will need supporting as they grow.
Soya beans are thirsty plants and crop best when watered regularly, especially once they start to flower and form pods.
Apply a thick layer of garden compost around the plants to help hold moisture in the soil and deter weeds.
Fertiliser is not usually necessary.
Keep seedlings and young plants weed-free, to reduce competition for light, water and nutrients.
Take care to protect seedlings and young plants from slugs and snails.
Most soya bean varieties sold in the UK grow to around 60cm (2ft) tall and are self-supporting. But a few taller varieties may be available and will need support – insert sturdy bamboo canes at the ends of the rows and loop string around them to hold the plants upright.
Edamame beans are immature soya beans, harvested in summer when the pods are still green, with plump beans inside. They can either be shelled or cooked in the pods (then shelled), and must be boiled for at least 10 minutes to destroy their natural toxins.
Ripe soya beans are ready for harvesting from late September, when the leaves start to fall from the plants, often leaving just brown stems with lots of hanging pods. The pods remain weatherproof during autumn, so you can pick as needed.
Remove the beans from their dry pods, then either cook straight away or spread out on a tray indoors to dry fully. Store the dry beans in an airtight container for use over winter. As with the immature beans, cook mature soya beans thoroughly to remove any natural toxins.
Soya beans are easy to grow and generally trouble-free, as long as they are kept warm and well watered throughout the growing season. In cool summers or colder regions, cropping may be reduced. Take care not to plant them out too early, and protect them with fleece or cloches to keep them warm while they get established.
Seedlings and young plants are vulnerable to slugs and snails.
The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.