Sowing Broad Beans: Autumn vs Spring, Depth and Spacing

Autumn sowing or spring sowing: pick one deliberately

Broad beans are the one legume that germinates in genuinely cold soil, from about 41F (5C), and that is what makes autumn sowing possible. Sown so the plants go into winter three to six inches (8 to 15 cm) tall, they sit through frost, root deeply while nothing else is growing, and crop three to four weeks earlier than spring-sown plants. The early crop matters because it flowers and sets pods before blackfly build up, which is the single largest pest problem this crop has.

Spring sowing is the safer route and the one to take on heavy, wet ground or in a climate with long hard freezes. Sow as soon as the soil can be worked and has drained, any time the top few inches are workable and above about 41F (5C). The plants grow fast in lengthening days, but they flower later, into the season when aphids are already flying, so you will spend more time pinching tips and watching the growing points.

There is no reason to choose only one. Many gardeners sow a short autumn row for the early picking and a longer spring row behind it, which spreads the harvest over six to eight weeks instead of dumping it all in one fortnight.

Judge autumn sowing by plant size, not by the date. Plants that go into winter above eight inches (20 cm) are soft, top-heavy and far more likely to be killed or flattened than short, stocky ones.

Depth, spacing and the double row

Sow the seed two inches (5 cm) deep, and closer to three inches (8 cm) in light sandy soil or for an autumn sowing where the seed benefits from being below the frozen crust. Broad bean seed is large and carries plenty of reserve, so deep sowing costs nothing in emergence and buys real protection from mice, birds and frost heave.

Space seeds eight to nine inches (20 to 23 cm) apart. The standard layout is a double row: two lines nine inches apart, with the seeds staggered between them, and 24 to 30 inches (60 to 75 cm) between one double row and the next. The double row is not just about fitting more in. The two lines lean on each other and on a single string run down each side, which is far less work than staking plants individually and keeps a laden row upright in wind.

Broad beans do not need rich ground and actively dislike fresh nitrogen, which produces tall soft growth that blows over and attracts aphids. Compost worked in the previous season is plenty. If your soil is acidic, a dressing of lime brings it toward the pH 6.5 to 7.0 this crop prefers, and it also reduces chocolate spot later.

1. Check the ground has drained Squeeze a handful of soil. If water runs out, wait. Broad bean seed sits in cold soil for two to three weeks before emerging, and waterlogged ground rots it in that time, especially in autumn.
2. Mark out the double row Two parallel lines nine inches (23 cm) apart. Push the seed in with a dibber or your finger to two inches (5 cm) and firm the soil over it. Firm contact matters more than watering.
3. Stagger the seed between the lines Set each seed opposite a gap in the other line rather than directly across. Staggering gives every plant light on both sides and lets air move through the row, which slows chocolate spot.
4. Water once, then leave the row alone One watering after sowing if the soil is dry. Do not water again until the shoots break the surface. Repeated watering of bare soil is the fastest way to rot a slow-germinating seed.
5. Cover against mice and pigeons Netting or a low cloche until the plants are four inches (10 cm) tall. Mice take the seed before it germinates and pigeons strip the first leaves, and both losses look identical from above: a gappy row with no explanation.

Starting in modules when direct sowing is unreliable

On cold wet ground, or anywhere mice are a known problem, start the seed in deep modules or three-inch (8 cm) pots in an unheated greenhouse, cold frame or porch. One seed per cell, two inches deep, kept just moist. Broad beans root deeply and quickly, so use the deepest cell you have and plant out within three to four weeks, before the root spirals in the bottom.

Plant out at three to four inches (8 to 10 cm) tall, at the same spacing as direct sowing, and bury the stem slightly deeper than it sat in the pot so it is anchored. Module-raised plants transplant readily as long as the rootball holds together. This route gives you most of the autumn-sowing advantage, an earlier crop that flowers ahead of the aphids, without gambling a whole row on the winter.

Do not start broad beans indoors in warmth. Heat produces long pale stems that flop the moment they meet wind, and this crop needs no help germinating. A cold, bright, sheltered spot gives short thick-stemmed plants that go straight out.

What to write down at sowing

Record the sowing date, whether it was autumn or spring, and how tall the plants were when the first hard frost hit. That last number is the one worth having. If you lost the row, it will tell you whether they were too big and soft or genuinely just unlucky, and next autumn you can move the sowing a fortnight either way with a reason behind it.

Note the position of the double row on a simple plan too. Broad beans leave nitrogen-rich root nodules behind, so the following crop in that spot benefits, and you also want to avoid putting beans back on the same ground for three years because chocolate spot and root rots build in the soil.