Runner Bean Growing Calendar: From Trench Prep to Lifting the Roots

The shape of the year

Runner beans are grown as annuals almost everywhere, but the plant is not one. It is a tender perennial with a swollen, tuberous root, and knowing that changes how the end of the season is handled. Everything before that follows a fixed sequence, and each stage has one decision in it that matters more than the rest.

The stages are: prepare the trench in winter, build the supports and sow after the frosts, get the plants onto the canes and mulched, water hard through flowering, pick every two or three days through the cropping weeks, then decide in autumn whether to lift the roots or start again from seed. Miss the winter trench and you will be fighting drought all summer; miss the picking rhythm and the crop ends a month early.

None of these steps is tied to a calendar date, because runner beans are governed by soil temperature at one end of the season and frost at the other. Read each stage by what the weather and the plants are doing rather than by the month.

Winter and spring: the work that decides the summer

The bean trench is the classic piece of runner bean practice and it earns its reputation. Dig out a trench a spade deep and a spade wide along the line of the row while the ground is bare in winter, fill the bottom half with compost, rotted manure or raw kitchen waste, and backfill. By sowing time it has settled into a band of moisture-holding material sitting directly under the root run, and that is what carries the plants through the hot weeks when flowers would otherwise drop.

Choose a sheltered, sunny site that is not in the lee of a hedge where air sits still. Runner beans need sun for flowering and bumblebee traffic, but they also need the row not to act as a windbreak in a gale. Rotate the position: three years between bean crops on the same ground keeps root and foot rots from building up.

Build the supports in the weeks before sowing, while there is nothing in the ground to damage. Then wait for soil temperature. A week of patience in spring is cheap; a rotted row is a fortnight lost plus the cost of reseeding.

1. Dig the trench in winter A spade deep along the row, filled with organic matter and backfilled. Let it settle for at least a couple of months before sowing over it.
2. Put up the frame before sowing Canes crossed and tied under a horizontal ridge pole, end pairs braced diagonally, working height seven to eight feet.
3. Sow when soil holds 54F (12C) Sow dry seed two inches deep, one per cane, with spares at the end of the row. Cover against mice and pigeons until true leaves open.
4. Mulch once the plants are a foot tall Three to four inches of compost or straw over thoroughly damp soil. This is the second half of the drought insurance the trench started.

Summer: flowering and the picking weeks

From the first flower bud to the last pick, the row wants one thing above all: a root zone that never dries out. Water deeply every four or five days in warm weather rather than lightly every evening, and feed with a high potash liquid every ten to fourteen days. Pinch the growing tips out when they reach the top of the frame, which both keeps the crop in reach and pushes the plant into side shoots and flower.

Expect twelve to eighteen days from an open flower to a pickable pod. Once picking starts, the rhythm is every two or three days without exception, taking every pod at size including ones you cannot use, because a single pod left to swell its seeds is enough to slow the whole plant down.

Runner beans keep flowering into autumn if they are watered and picked, and the last few weeks are often the easiest, with cooler nights giving better set than midsummer did. Do not give up on a row that stopped setting in a heatwave: it will usually come back into full crop once the weather breaks.

Autumn: lifting the roots, or not

When frost has blackened the tops, cut the vines off at ground level and leave the roots in the soil rather than pulling them, because the nitrogen-rich nodules break down where they will do next year's crop some good. That is the ordinary treatment, and sowing fresh seed each spring is what most growers do.

The alternative uses the fact that a runner bean is perennial. Under the soil is a cluster of pale, swollen tuberous roots, and in a mild climate where the ground does not freeze deeply these survive in place under a thick mulch and shoot again in spring, several weeks ahead of a fresh sowing. Where the ground does freeze, lift the tubers after the tops are cut down, shake off loose soil without washing them, and store them dry in a frost-free shed in boxes of dry compost or sand, exactly as you would dahlia tubers. Replant them once frost has finished.

Stored roots are worth trying but they are not a guaranteed improvement. A second-year root produces earlier flowers but often a shorter total crop, and any root that feels soft or shows rot when you lift it should be thrown away rather than stored. Many growers keep a few roots as an early row and sow seed as well for the main crop, which is the sensible compromise.

Whichever route you take, clear the frame, scrub and store the canes dry, and clear the debris. If halo blight was present, that debris goes to the bin, not the heap.

A lifted runner bean root looks unpromising: pale, lumpy and slightly translucent. That is normal. Firmness is the test, not appearance.

The season's record

Four dates make next year easier: the day you sowed, the day the first flower opened, the day of the first pick, and the day the crop effectively finished. Together they show whether your sowing date suits your site, how long your cropping window really was, and which spell of weather cost you anything.

Add a sketch of where the row ran with a measurement from a fixed edge, so the three-year rotation is real rather than remembered. If you lifted roots, note how many went into store and how many came out sound the following spring, because that ratio is the only honest way to judge whether storing them is worth the trouble at your site.