How to Sow Green Beans: Soil Temperature, Depth and Spacing

Soil temperature decides everything

A bean seed swells with water within hours of going into the ground, and if the soil is colder than about 55F (13C) it sits there swollen and does not germinate. Cold, wet soil rots beans faster than any other common vegetable seed. Wait until the soil at sowing depth is steadily above 60F (15C) and all frost risk has passed, and germination takes five to eight days instead of three weeks.

The difference in the finished crop is smaller than people expect. Beans sown a fortnight late in warm soil routinely overtake beans sown early in cold soil, because the early sowing spends that fortnight underground losing seed to rot. There is no advantage in rushing, and pole beans in particular need warmth to climb rather than sulk.

If you must sow early, warm the bed with black plastic for a week beforehand and lay a floating row cover over the row after sowing. Both are worth about a fortnight of season.

Sow direct, and sow in stations

Beans resent root disturbance, so sow where they are to grow. Sow three seeds together at each station, an inch (2.5 cm) deep, and cover with fine soil pressed down lightly with the back of your hand. Sowing in threes is not waste, it is insurance: birds, slugs and cold patches take seeds unevenly, and a station with three seeds almost always gives you something.

Depth matters more than most seed. Half an inch and the seed dries out and the seed coat stays stuck on the emerging leaves. Two inches and it exhausts itself pushing up. One inch is right in most soils, an inch and a half in light sand.

1. Water the drill, not the seed Soak the bottom of the drill before you sow, then sow into the damp soil and cover with dry soil. This gets the seed germinating without capping the surface into a crust.
2. Three seeds per station Space the three seeds an inch or two (3 to 5 cm) apart within the station so their roots do not tangle when you thin later.
3. Do not soak the seed first Presoaked bean seed splits its coat and rots in the ground far more readily than dry seed. Sow beans dry, every time.
4. Cover against birds Pigeons and jays pull emerging beans out of the ground for the seed still attached. Netting or a row cover until the first true leaves open prevents it entirely.

Spacing depends on bush or pole

Bush beans finish at about knee height and carry their crop over two to three weeks, so they are grown in blocks or short double rows. Pole beans climb six to eight feet (180 to 240 cm) and crop for two months, so they are grown at wider stations against a support that goes up before you sow.

Give both more room than looks necessary while the plants are small. Beans close over their spacing completely by midsummer, and a crowded stand stays damp after rain, which is where rust and gray mold start.

Thin to two, and cut rather than pull

Once the first true leaves have opened, reduce each station to the two strongest seedlings. Leaving all three gives you thin, drawn plants that flop and set fewer pods. Cut the surplus off at soil level with scissors instead of pulling, because pulling drags the roots of the two you are keeping.

Keeping two rather than one is deliberate. Beans support each other, produce a better yield per station, and if one is taken by a cutworm you still have a plant on that station. Below about 45F (7C) at night the survivors will stall for a few days after thinning; that is normal and they pick up.

1. Thin at the first true leaf The two rounded seed leaves come first, then the first proper trifoliate leaf. That is the moment to thin, roughly ten days after emergence.
2. Keep the sturdy, not the tall Choose the two with the shortest gap between the seed leaves and the soil. The tallest seedling in a station is usually the weakest.
3. Earth up as you thin Draw an inch (2.5 cm) of soil around the base of the plants you keep. It steadies them against wind and encourages roots from the lower stem.

Successional sowing keeps beans coming

Bush beans crop hard for two or three weeks and then stop, so one sowing gives you a glut and then nothing. Sow a short row every two to three weeks from late spring until about ten weeks before your first autumn frost, and you pick continuously instead. Pole beans crop over a much longer window, so one sowing plus a single follow-up is usually enough.

This is worth writing down. Note the sowing date, the emergence date and the date of the first picking for each row, and after one season you will know exactly how far apart your own successions need to be. Note the soil temperature at each sowing too, because that is what explains a row that came up badly.

Beans fix their own nitrogen once the root nodules form, so do not enrich the bed with high nitrogen material before sowing. Rich ground gives you a magnificent plant carrying almost no pods.