Soybean: growing, harvest & uses

If you like fresh edamame and tofu, why not try your hand at growing your own soy? Here are our top tips on choosing soya bean varieties, sowing and harvesting.

Soybean (Glycine max) is a versatile plant that can be cultivated in gardens and on balconies or patios. Below is everything you need to know about planting, caring for and using soya beans.

Soybean: origin and properties

Soya bean plants originate from northern China and Japan and are the world’s most widely cultivated protein and oil plant by acreage. Soy belongs to the legume family (Fabaceae) and are closely related to the pea (Pisum sativum), lentil (Lens culinaris), lupin (Lupinus) and bean (Phaseolus vulgaris). Depending on the variety and growing conditions, soybean plants reach a height of anywhere from 40 to 100cm. Soy plants are annuals that feed via a deep taproot. Like most legumes, soy beans have root nodules on their roots which form a symbiotic relationship with nitrogen-fixing bacteria. Soy-specific bacteria (Bradyrhizobium japonicum) settle in clusters on the soy bean plant’s roots and collect nitrogen from the soil air. The bacteria then exchange oxygen with the sugar produced by the photosynthesis of the soy plant. Through this bacteria-driven process, the soy plant is fertilised.

Soy bean plants are three-parted plants with a feathery, hair-like texture that covers the whole plant. The plant’s self-pollinating, white or pale purple small soybean flowers bloom between May and July. After fertilisation, elongated, hairy brown pods will form, each with two to three oval-round seeds. When harvested, these young, unripe, podded seeds together are what is known as “edamame”, Japanese for “bean on a branch”. Between September and October, when the seeds ripen, the entire soy plant gradually dies. Dry pods will finally open and distribute their seeds in the surrounding area. Soybean seeds can be creamy white, beige, brown, green, black or mottled, as well as speckled and marbled.

The best soybean varieties

All soya bean varieties can be harvested for edamame beans and dry soya beans. The only decisive factor for growing in the UK is that the soy bean variety is early ripening. Early ripening soybean varieties mature between 75 to 100 days after sowing, between August and September, while late ripening varieties do not ripen until October. With the latter, there is a risk that in our cool and rainy summers, the soy beans will not reach full ripeness. Here are some suitable soy varieties for our climate:

• ‘Agate’: Very early soy bean variety with light to dark brown seeds. The small-growing plants produce abundantly and are ready for harvesting after 90 days.
• ‘Chiba Green’: Especially tasty edamame soy beans with a very short maturing period. Harvesting is possible 75–90 days after sowing.
• ‘Envy’: Up to 80cm tall soy bean plants with shiny green beans. Unripe pods can be harvested for edamame from August onwards and the plant’s dry beans from the end of September to October.
• ‘Fiskeby V’: Very early, light yellow soybean variety best known for crunchy and sweet edamame. Its edamame beans should be harvested from August and dry beans from October onwards.
• ‘Green Shell‘: Early and sturdy edamame soy bean plants with a short ripening time of about 100 days. Harvesting extends from mid-August to the end of October.
• ‘Hokkaido Black’: A vigorous and bushy black soy bean variety that is adapted to cooler regions. They are served alongside edamame at the Japanese New Year as the dessert kuromame.

How to grow soybeans in the garden

The ideal location for soya bean cultivation is sunny with soils that warm up quickly, are well-drained and retain water well. The soil’s pH value should be between 6.5 and 7. Sow soybeans outdoors once the soil temperature reaches above 10°C, usually between April and mid-May. Since soya beans need a lot of time to mature, make sure to sow before June. Alternatively, pre-sow your soybeans indoors from April and transplant in May. The sowing depth is 3 to 4cm, because soybeans are strictly dark germinators. Keep a plant spacing of 10 to 15cm, with a row spacing of 30 to 50cm. At temperatures of 12 to 20°C, germination takes place after around 10 to 20 days.

If you want to grow soy in pots, choose a pot with a volume of at least 5 litres and a drainage hole. Fill the pot with a high-quality potting soil, such as our Plantura Organic All Purpose Compost, then sow soy bean seeds and water well. Around three to four soy plants can be cultivated together in a 5-litre pot.

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To get the best growth and high yields, we recommend giving the soya bean plants a boost with their natural symbiotic partners, the previously mentioned nitrogen-fixing bacteria, before sowing. These microorganisms are available for hobby gardeners in small liquid batches, which usually come with a sugar-rich gluten mixture. Mix the sugar and bacteria in a spray bottle and then apply it directly to the soybeans. Plant the inoculated soybean seeds straight after this, as the bacteria are extremely sensitive to light and will quickly die when exposed.

Soy is a good preceding crop as it builds up nitrogen in the soil. After this crop, high-yielding vegetables such as tomato (Solanum lycopersicum) or courgette (Cucurbita pepo subsp. pepo convar. giromontiina) grow particularly well. Soy beans themselves should only be planted in the same location every three years.

Summary: growing soybeans

• Ideal location: warm and sunny location with well-drained, water-retentive soil
• For optimal growth: spray the soybean seed with root nodule bacteria just before sowing
• Sow indoors from April or directly outdoors when the soil reaches 10°C, until the end of May at the latest
• Sowing depth: 3–4cm, plant spacing: 10–15cm, rows spacing: 30–50cm
• At 12–20°C, germination takes place after 10–20 days
• For pre-sowing, transplant from mid-May into beds or tubs with high-quality potting soil
• Crop rotation: plant soy beans in the same location only every 3 years

Soybean plant care

Soy plants hardly need any care after germination; fertilisation is not necessary if enough bacteria have settled on the roots. That being said, a good supply of water is essential until a sufficiently large root system has developed, especially during flowering between June and August. So you may need to water the young and flowering plants. It is also important to remove weeds until the soy plants have formed a dense stand. Apply a mulch layer of lawn clippings and other materials to reduce water loss through evaporation and help keep the weeds at bays. At the same time, mulch also provides food for soil organisms and helps build up organic matter.

Common soybean pests and diseases: As things stand, soybean plants are only rarely affected by pests and diseases here in the UK. However, painted lady butterfly caterpillars (Vanessa cardui) can lay eggs on soy bean plants and cause severe feeding damage. Pigeons and crows like to dig up freshly planted seeds and young seedlings. Young soy shoots are also a welcome snack for rabbits, hares, and deer. A protective, fine-meshed net over the crop is a simple and effective remedy.

Harvesting soybeans

Firstly, harvesting edamame is similar to harvesting runner beans. Soy bean pods should be completely green and not yet woody or fibrous, and the seeds inside should be clearly visible. For most varieties, the edamame harvest begins about 80 to 100 days after sowing. Do you want to harvest dry soy beans to make your own soy milk or tofu? Then you should wait until the entire soy plant has turned brown. Depending on the variety, this is between September and the end of October. When ready, dry pods on the plant will rustle when touched. Ideally, harvest in the morning when the pods are still damp and tough from the dew. This is because dry, ripe pods tend to break open in the harvesting process. Use garden shears to cut the entire plant off at the bottom and dry it out for a few days in a bright, warm place. Afterward, remove the beans from the pods by hand or thresh them out in a bag.

Are soybeans good for you?

There are many health benefits of soybeans. Soya beans are both healthy and filling: 100 grams contains about 150 kcal. They contain a large amount of proteins and fats: the very high protein content of 30 to 50% of soy beans is a valuable source of nutrition for people and animals. When dry, soy beans also contain a considerable amount of oil, between 18 to 24%. These unsaturated fatty acids are extraordinarily healthy. If that’s not enough, soya beans are also packed with a variety of minerals and vitamins, especially vitamin E, potassium, calcium, and magnesium.

Using soy beans

Soy is playing an increasingly important role in human nutrition. Lots of meat and milk substitutes for vegetarian and vegan diets are primarily made from soy. In Asian countries, soybean oil is often used for cooking and stir-frying. It’s also possible to make tofu and soy mince from dry soya beans. Roasted soya beans also make a delicious healthy snack. Fermented soybeans are particularly easy to digest, in the form of soy sauce or in the Japanese dish natto. To prepare edamame, briefly cook the young, still green and juicy beans in their pods and simply serve with salt and other spices.

Is soy poisonous?

In their raw state, young soybeans, ripe seeds and all green parts of the plant are poisonous and can cause nausea and vomiting when consumed in excess. This applies to humans and animals, with the exception of rabbits. Both edamame and the dry soy beans should therefore only be enjoyed after they have been well cooked.

Like soybeans, the chickpea (Cicer arietinum) belongs to the legume family and can also be grown on balconies and in gardens. Here are our expert tips on choosing varieties, planting and care.