Like other legumes, broad beans are perfect for fixing nitrogen into the soil in your polytunnel. One of the good things about growing broad beans in a polytunnel, undercover, is that this will allow for an autumn planting which will allow you to start picking broad beans much earlier in the year than would be possible if you were growing them outside. Of course you can also plant in the spring and so can enjoy broad beans over a long period.
By fixing nitrogen from the air, broad beans can help keep the soil in your polytunnel healthy and productive. This also means that they are a good companion plant for a whole range of different crops, especially leafy crops with higher nitrogen requirements. By using a rotational bed system in your polytunnel, you can ensure that all the polytunnel sections receive this help. If you are very short on space, dwarf varieties of broad beans can also be grown in pots.
Broad beans can be sown directly into the soil in your polytunnel in the autumn and in the spring. However, rodents and other pests are attracted to the direct sown beans and you may lose your crop before it even gets started. For this reason, many gardeners will choose to start their broad beans in containers out of harms way and move young beans to their final growing position once they have grown a little. Alternatively, young beans can be protected with cloches (you can make these from plastic drinks bottles cut in half), pushed into the soil around the beans. If you start broad beans inside, make sure you do not keep them in a heated room or they may not germinate.
Sow in double rows 20cm apart with 20cm between rows 4cm deep. Broad beans will need some sort of support as they grow. Garden canes or long branches with string strung between them can be used to surround a double row of broad beans and keep them upright. Water is not required regularly until the beans start to flower, at which point you should water well, then do so again two weeks later.
Flowers on the broad beans will do a great job of attracting bees and other pollinating insects. Make sure you leave the doors of your polytunnel open as much as possible when the beans are flowering so the pollinators can come and go as needed.
As soon as the first pods begin to form, pinch off the growing tip of each plant. This will help prevent a blackfly infestation and can also speed up the harvest and help ensure a good crop.
Broad beans sown in autumn can be harvested from May, while sowings from March onwards can be harvested between June and September. Pick some pods when they are around 7cm in length – these can be cooked and eaten whole. Mature beans are best harvested when these are visible through the pod. Do not leave the beans too long, as they can get very tough at later stages of growth.
Autumn sowing will provide bens in early June. Autumn sowing is only possible under cover.
Maincrop sowing begin in March and at monthly intervals until May.
Under cover - February
In open - March to May
Expected picking time – June to September.