Germination temperature
Favourable soil temperature 25-33 °C (77-91 °F); in cool climates wait until the soil is above 15 °C (59 °F).
Legume growing guide
Edamame is soybean picked green, when the beans fill the pods but are still soft. It needs warm soil, the right inoculant and attention to day length, because soybean flowering is triggered by long nights.
Favourable soil temperature 25-33 °C (77-91 °F); in cool climates wait until the soil is above 15 °C (59 °F).
1.3-3 cm (0.5-1.2 in); no deeper than 5 cm (2 in).
Seedlings emerge in about 5-7 days in warm soil.
No light needed for germination. Day length later controls flowering.
Bradyrhizobium japonicum inoculant; no soaking.
Direct sow.
Inoculate the seed with Bradyrhizobium japonicum, the soybean-specific nodule bacterium; University of Florida IFAS calls this highly recommended where soybean has not been grown before. Tamil Nadu Agricultural University (TNAU) uses three packets (600 g per hectare) of Rhizobium culture mixed with rice kanji as a sticker; dry the seed in shade for about 15 minutes and sow. For a garden, follow the dose on the inoculant packet.
Not needed. Soybean seed takes up water quickly; it needs to absorb about half its own weight in water before it germinates.
Not needed. Soybean is a warm-season crop with no cold requirement.
Not recommended. The first hours of water uptake are the most sensitive: University of Nebraska trials found the critical period within the first eight hours after planting, and chilled water during that time cut emergence sharply; damaged or cracked seed coats and very dry seed (below 13% moisture) raise the risk. Sow dry seed into warm, moist soil instead.
Soil at 25-33 °C (77-91 °F) is favourable for edamame germination. In cool regions sow only once the soil is above 15 °C (59 °F). Very hot, dry soil can also hold germination back, so water before sowing in summer.
The University of Florida gives a normal depth of 1.3-2.5 cm (0.5-1 in), up to 5 cm (2 in) in gravelly or dry soil; TNAU dibbles seed 2-3 cm (0.8-1.2 in) deep. Deeper than 5 cm (2 in) gives late, uneven emergence.
Well-drained, aerated soil. Large, oily soybean seeds need more oxygen than small vegetable seeds and fail easily in waterlogged soil.
TNAU irrigates straight after sowing and again on the third day. Avoid standing water: soybean is very sensitive to excess moisture, and cool, wet soil increases seed rot.
Not needed for germination.
About 5-7 days to emergence in warm soil; longer in cool soil.
Not recommended; sow where the plants will grow. TNAU spaces grain soybean 30 cm (12 in) between rows and 5 cm (2 in) between plants; thin to a little wider for bushier edamame plants.
Nodules form mostly in the top 20-25 cm (8-10 in) of soil, and nitrogen fixation begins at about the second trifoliate leaf stage. In trials in Miami, Florida, flowering started about five weeks after planting.
Cause: seed sown too deep, cold water during the first hours of uptake, waterlogged soil or old, low-vigour seed. Fix: sow 2-3 cm (about 1 in) deep in warm, moist, drained soil, do not soak, and resow gaps promptly.
Cause: soybean measures night length, and long nights trigger flowering. Varieties are bred for particular latitudes, so a variety sown where nights are longer than it is adapted to can flower early. Fix: sow in the recommended local season and use varieties suited to your region.
Cause: no effective nodules, usually because the soil has no soybean bacteria. Fix: inoculate with Bradyrhizobium japonicum the next time you sow.
Cause: harvest was missed; edamame pods pass the right stage within about a week. Fix: check plants daily as pods fill.
Soybean is a short-day crop. In Tamil Nadu, TNAU sows soybean in June-July, September-October and February-March; the June-July sowing is the kharif (monsoon) season. In temperate climates sow after the soil warms in late spring.
Avoid water stress from flowering to harvest, but never leave the bed waterlogged.
Pick when pods are still bright green and the beans are 80% to full size. In the Florida trials this was 60-76 days after planting, with most pods ready within 10-11 weeks.
Caterpillars, thrips and insects that feed on buds and developing pods are the main pests reported in edamame; check plants once flowering starts.
Grow your own sweet green soybeans for steaming straight from the pod.
Yes, if soybean has not grown in that soil before. Soybean nodulates with its own bacterium, Bradyrhizobium japonicum, so an inoculant labelled for soybean gives the plants their own nitrogen supply.
No. The first hours of water uptake are the most sensitive stage, and cold water at that point damages the seed. Sow dry seed into warm, moist soil.
When pods are plump and green and the beans fill 80% or more of the pod, roughly 60-76 days after sowing in warm conditions. Pods turn yellow within about a week after that.