No. 9
BROAD BEANS
Vicia faba
Family: Leguminosae
Broad bean seed saving guidelines also available as a PDF document (165Kb)
Broad beans range in height from 60cm to 2m. There are no clear botanical distinctions between field beans and ones grown in gardens.
The flowers are perfect and self-pollinating but cross-pollination will readily occur due to insect activity. The flowers open early in the morning and do not shut. The anthers shed pollen the night before the flower opens, but this does not reach the stigma until the flower is tripped, usually by insects.
Growing and Roguing
- Broad beans being grown for seed should be grown as you would for an edible crop. However, you should start sowing early so that the growing season is as long as possible to allow the pods to mature and dry.
- As broad beans are outbreeders (that is, they cross-pollinate), you need to grow as many plants as possible, 24 as a minimum. This allows for roguing and selecting, and helps maintain the health and diversity of the variety.
- Some plants may produce noticeably different foliage or pods from the majority of the plants; these should be removed. Any plants that produce flowers of a different colour should be immediately removed. However, if the flowers have opened, it is possible that they could already have already cross-pollinated.
- Seed that is the result of crossing will usually reveal itself in the next generation as a visible increase in the variability of the plants. There will be no visible signs of crossing until the second generation, so go back to the seeds saved from two harvests previously for seed that should be pure.
Pollination and Isolation
Dry broad bean pods
Broad bean flowers are attractive to bees and a good deal of cross-pollination can occur between broad bean varieties and any field beans growing nearby. We recommend that you grow only one variety each year.
Commercial seed producers grow broad beans a minimum of 1,000m apart. If this is not practical and you are saving only for your own use there are things you can do to reduce crossing. ‘Living barriers’ in gardens help reduce the risk of cross-pollination, e.g. tall crops of a different species. It also helps if you grow large numbers of plants in blocks rather than rows — the plants in the centre of the block would produce the purist seed.
Isolation cages can be used, but bagging is practically impossible. Broad beans can self-pollinate if no insects are introduced, but with less successful results.
Harvesting
Allow the pods to dry on the plants if possible, but be aware that they may rot. As they ripen pods blacken and lose their sponginess. The pods are ready to clean when they have turned black and crispy. Whole plants can be brought in to dry in a warm, airy place if necessary.
Cleaning
Cleaning refers to the removal of chaff and debris, leaving only seed. Cleaned seed keeps better.
Broad beans can be difficult to thresh so hand shelling is best, especially if you only have small quantities to deal with. If the seeds are not quite dry when podded, spread them out to dry further.
Winnowing is best done outside in a stiff breeze. Pour the beans steadily from one container to another, allowing the wind to blow the chaff away. Repeat until the chaff is gone and you are left with only seed. Do this over a tarpaulin, in case a sudden gust upsets the container and spills the seed.
Bean Seed Beetle damage
You may notice small holes in the beans. These are caused by bean weevil, or bean seed beetle, larvae. These can devastate your crop of beans as they eat the endosperm away when they hatch. The beetles can eat through paper envelopes. If they start feeding on the seed embryo the bean will not germinate. Adults often emerge in storage and can complete several generations before planting time. Be sure to remove all trace of any beetles you may find. All life stages can be destroyed by a 7-day minimum stay in a fridge. Freezing a batch of dried, infested seed for 5 days in the freezer should kill the beetles but not the seeds.
Ensure beans dry out fully afterwards and before storing. Hand-podding allows any bad seeds, or seeds infested with bean seed beetle, to be identified and discarded. Shaking packets and covering seeds in a light oil can help guard against future damage. The beetle damage does not affect germination, so long as the embryo is not attacked, so you can keep the seed for home use (as long as they don’t still have the beetles in them) — but they do look unsightly.
Storage
Broad bean seeds should last in storage for at least three years.
Returning Seed to HSL
It is important that seed returned to HSL is not cross-pollinated. Do not send us seed that you suspect might have crossed.
Remove any beans with obvious bean weevil damage. Do not return them to HSL. Retain any that have not sustained damage to the embryo for your own use. If you have frozen the seed please note this on the packet.
Seed must be completely dry and fully cleaned. Seed that retains moisture can go mouldy in transit and will have to be discarded. It can take a few days to get to us in the post. Pack it in breathable material (e.g. a paper envelope or cotton bag) and place it in a padded envelope or stout box to protect the delicate seed from impact damage, before sending it in the post.
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