Broad bean

Light and exposure

Broad beans like full sun but do perfectly well without it, as long as the spot stays open and airy. Unlike basil or tomatoes, light is not what limits growth here, space is: the stems shoot up fast and tall, often past eighty centimetres, and a row planted in the shelter of a hedge or wall goes down flat at the first proper gust.

Choose a spot that breathes, sheltered from the worst gusts if you can manage it, rather than one that is simply sunny all day. An open spot that is not swept by the prevailing wind already solves half your future staking problems.

Watering

At sowing time, whether autumn or late winter, the soil’s natural moisture is more than enough here: broad beans germinate and grow during the wettest season of the year and never ask for watering at that stage. Too much water at the start actually rots the seed before it comes up, especially in heavy, poorly drained soil.

Everything changes at flowering and pod fill, in May and June. That is when water really matters: a dry spring at the wrong moment gives short, poorly filled pods. Water at the base if rain turns scarce during that period, and never wet the foliage, rust and chocolate spot both love standing moisture on the leaves.

Soil and repotting

Broad beans are not fussy about soil and even tolerate heavy, clay ground, which is unusual for a legume. A deep, cool, well structured soil suits them perfectly, as long as it does not stay waterlogged over winter, or the roots suffocate and the seeds rot.

As with peas, skip the nitrogen fertiliser: broad beans feed themselves through their nodules, and extra nitrogen just pushes them into leaf at the expense of pods. A little well rotted compost worked in during autumn or late winter is plenty, and avoid sowing beans in the same spot several years running, or the same diseases build up in the soil.

Temperature and humidity

This is the broad bean’s strong suit and what sets it apart here: it germinates from as little as four or five degrees in the soil, grows well between ten and twenty degrees, and well established plants shrug off light frost down to around minus five without damage. The more tender autumn sown seedlings handle hard frosts a little less well, but usually pull through under our climate, especially with a bit of mulch.

The real limit is heat, not cold. Past twenty five degrees the flowers abort, black aphids explode in number, and the plant wears itself out fast. That is exactly why it is sown so early here: flowering and pod fill need to be behind it before the July heat sets in.

Pruning and upkeep

Broad beans are not pruned in the usual sense, but two moves really matter. First, earthing up: draw soil around the base of the stems, as you would for potatoes, to stabilise them. Second, staking, which is not optional: the stems are hollow and brittle, and a row of broad beans in full growth goes over at the first properly strong gust. Frame the row with stakes linked by taut string on both sides, or stretch netting alongside it, so the plants lean against it instead of falling.

The single most useful move is topping: as soon as the first pods appear, pinch out and remove the top ten centimetres of each stem. That tender growing tip is exactly where black aphids (Aphis fabae) mass first in spring. Topping stops them settling in their tracks and keeps them from colonising the whole plant, while pushing the bean to put its energy into filling the pods already set rather than growing taller. The removed tips are good eating too, wilted in butter like spinach.

Pests and diseases

Rust (Uromyces viciae-fabae) shows up as small orange pustules on the leaves, mostly late in the cycle in mild, damp weather, very much our specialty. It weakens the plant without necessarily killing it, but cuts the harvest if it takes hold early. Chocolate spot (Botrytis fabae) is more serious: reddish brown blotches, shaped rather like chocolate, appear on leaves and stems in mild, humid weather, often after a stretch of rain. Left unchecked, it can defoliate the plant.

The real classic is black bean aphid (Aphis fabae), which swarms the tops of the stems in spring and forms proper sticky black colonies. It weakens the plant, spreads viruses and draws ants. Topping the plant as the first pods appear is by far the best defence, much more effective than a late treatment. Keep the rows airy, avoid watering the foliage, and do not sow broad beans in the same spot year after year to keep the pressure from these diseases down.

Propagation

Broad beans are sown only in place, straight into the garden: they dislike being transplanted, and pricking out too often damages their fragile roots. Sow in rows about forty centimetres apart, five centimetres deep, spacing the seeds twenty to twenty five centimetres apart, or in stations of two or three seeds every twenty centimetres. Freshly worked soil, neither waterlogged nor bone dry, gives the best emergence.

You can also save your own seed. Let a few good pods dry completely on the plant at the end of the season, until the pod blackens and turns brittle, then shell and store the seeds somewhere dry. They resow very well the following year, provided you start from a non hybrid variety, which most shop bought broad bean varieties are.

Month-by-month care calendar

Green Hub tips

• Sow early, as soon as you can: broad beans shrug off light frost down to around minus five degrees, whether autumn sown (October to November) under a mild winter or, safer here, late winter sown from February.
• Top the stems as soon as the first pods appear, removing the top ten centimetres. It is the best way to stop black aphids before they settle in, and it speeds up pod fill.
• Stake every row as a matter of course, with posts and taut string on both sides. The hollow stems go over easily in the wind once loaded with pods.
• Never add nitrogen fertiliser: broad beans fix their own through their root nodules and even enrich the soil for the next crop.