Germination temperature
Fastest at about 20 °C (68 °F); still germinates at 5 °C (41 °F), only more slowly.
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Fava (broad) beans are a cool-season legume that germinates in cold soil and crops best before the weather turns hot, which makes them a rabi crop in India. This guide covers deep sowing, why a long soak can kill the seed, inoculation and the two problems that matter most: blackfly and chocolate spot.
Fastest at about 20 °C (68 °F); still germinates at 5 °C (41 °F), only more slowly.
5-7.5 cm (2-3 in) in temperate gardens; in an Indian field trial 10 cm (4 in) gave the best yield.
In laboratory tests half the seeds germinated in 3 days at 20 °C (68 °F) and in 9 days at 5 °C (41 °F); field emergence is slower.
No light needed; the large seed is buried deeply.
Rhizobium inoculant on new ground. Do not soak for long.
Direct sowing is usual; seeds can also be started in deep pots and planted out after hardening off.
Sow the dry seed into moist soil. Where peas or beans have not been grown before, coat the seed with a Rhizobium leguminosarum inoculant (the pea and faba bean group) just before sowing so the roots form nitrogen-fixing nodules.
Not needed. Fava bean seed takes up water readily, which is exactly why a fast, long soak can harm it.
Not needed. There is no cold requirement; the seed germinates in cool soil without any treatment.
Avoid long soaks. In tests at India's National Bureau of Plant Genetic Resources, broad bean was among the legumes most sensitive to imbibition injury: soaking for 16-20 hours increased the number of seeds that failed to germinate. Slow rehydration reduced the damage. If you want to pre-start seed, let it take up water slowly from a damp (not flooded) medium instead of a bowl of water.
Germination was fastest at 20 °C (68 °F) in a temperature study, and the total germination percentage did not change between 10 and 30 °C (50-86 °F). At 5 °C (41 °F) it was about 4% lower and much slower. Sources give different optimum temperatures, but they agree that cool soil is fine for this crop.
The RHS recommends 5-7.5 cm (2-3 in) deep with the seed scar (hilum) facing down. In a trial at the ICAR Research Complex for Eastern Region, Patna, sowing 10 cm (4 in) deep gave a significantly higher seed yield than shallower sowing. Use the deeper end in light, quickly drying soils.
A deep, well-drained soil. In the Patna trial, raised beds gave better germination (85.7%) and higher yield than flat beds, which is useful where winter irrigation can waterlog flat ground.
Sow into soil that is moist but not saturated, then water once. Do not keep seed in waterlogged soil.
Not required. The seedling pushes up from deep soil on its own reserves.
Several days in mild soil and noticeably longer in cold soil; laboratory times to 50% germination were 3 days at 20 °C (68 °F) and 9 days at 5 °C (41 °F).
If you start seeds in pots, use deep pots, harden the plants off and plant out in early to mid spring (temperate) or early rabi (India). Space plants 15-23 cm (6-9 in) apart in rows 45 cm (18 in) apart (RHS); in the Patna field trial, square spacing of 30 x 30 cm (12 x 12 in) gave the highest yield.
Tall varieties need support: put a stake at each corner of the row and run string around them every 30 cm (1 ft). Dwarf varieties mostly hold each other up.
Cause: imbibition injury. Fava bean seed is damaged by fast, prolonged water uptake. Fix: sow dry seed into moist soil and sow a few spare seeds at the row ends to fill gaps.
Cause: blackfly colonise the soft young tips. Fix: when the lowest flowers have set small pods, pinch out the shoot tips. This removes the favourite feeding site and sends energy into the pods. The tips can be cooked like spinach.
Cause: chocolate spot, one of the most common fungal diseases of broad beans. Fix: avoid crowded, humid plantings, keep air moving between rows and water the soil rather than the leaves.
Cause: mice eat sown seed. Fix: start seed in pots indoors, or protect the row.
Fava bean is a cool-temperature crop. In the Indian plains sow it in the early rabi season, after the monsoon, so that flowering and pod fill happen in the cool months; in temperate gardens sow in early spring, or in autumn with hardy varieties in mild areas.
For shelling, pick pods when they are full but still fairly small and the bean scar is white or green; a black scar means the beans are getting tough. Pods about 5 cm (2 in) long can be cooked whole. Pick every few days, starting with the lower pods.
After harvest, cut the plants at the base and leave the roots in the soil to return nitrogen to the bed.
People with the inherited G6PD enzyme deficiency can have a serious reaction (favism) to fava beans. Anyone with that condition, or a family history of it, should not eat them.
Sow fava beans in the cool season for tender green beans or a dry-seed harvest.
It is better not to. Research at India's National Bureau of Plant Genetic Resources found broad bean among the legumes most easily damaged when seed takes up water too fast; 16-20 hour soaks increased germination failures. Sow dry seed into moist soil.
In the early rabi season, once the monsoon is over and the weather is cooling, so that the crop flowers and fills its pods in the cool months.
Deeper than most vegetable seeds: 5-7.5 cm (2-3 in) is the usual garden depth, and an Indian field trial got the best yield at 10 cm (4 in).