When to Harvest Black Soybeans: The Green Window and the Dry Crop

One plant, two harvests, and you must choose

A black soybean can be picked green, with the beans plump and still soft inside the pod, or left to the very end of the season for hard dry beans. These are not two stages of one harvest. Picking green takes the pods before the plant has finished loading them, and a plant picked green is finished; leaving the crop for dry beans means giving up the green picking entirely on that plant.

The green picking from a black-seeded type is the reason many people grow it. The pods are larger and fatter than an ordinary soybean's, with two or three big beans rather than three small ones, and the flavor is denser and sweeter because the plant has spent a longer season loading sugar into fewer, bigger seeds. The trade is that you get one short window rather than a run of picking.

If you want both, split the block. Mark half the plants for green picking at the start of the season and leave the rest untouched for dry beans. Deciding this in midsummer, when the pods are already forming, always ends with you picking a bit of everything and getting a poor version of both.

Judging the green window, which is narrow

Pick green when the pods are still green and firm but visibly bulging, with the outline of each bean clear through the pod wall, and when a bean squeezed out is plump, soft and fills its side of the pod completely. On a black-seeded type the beans at this stage are usually pale green with a faint dark blush at the edge or around the eye, which is the seed coat pigment beginning to develop. A blush is fine. Fully dark beans are past it.

The window is roughly ten days, and it is shorter in hot weather. Before it, the beans are flat and taste of nothing. After it, the pod wall goes fibrous, the beans firm up and lose their sweetness, and the crop turns into an inferior version of the dry harvest without being any use as one.

Test rather than guess. Open one pod from the middle of the plant every couple of days once the pods look full. The lowest pods on the plant fill first and the top ones last, so the middle of the plant is the honest sample.

Pick whole branches rather than individual pods. Cut the branch off, strip the pods indoors, and take the entire plant over two or three days rather than picking over it for a fortnight. These pods lose quality quickly once they pass their peak, and a plant left half-picked ends up as neither harvest.

1. Start opening pods when they look full One pod from the middle of a plant, every second day. The beans should be plump and soft and fill the pod, with at most a dark blush at the edge.
2. Cut branches, not single pods Take whole branches with pruners and strip them under cover. It is faster, and it stops you picking over the same plant for two weeks.
3. Clear each plant within three days Once a plant is in its window, take all of it. Pods left behind go fibrous and are then neither a green crop nor a dry one.
4. Cool the pods quickly Get them out of the sun the moment they are cut. Sugar in the beans converts fast in a warm pile, and the flavor is the whole point of the green picking.

If the beans have already gone fully dark and hard inside a green pod, that plant has left the green window. Leave it standing and let it join the dry crop rather than picking it now.

The dry crop and the shattering deadline

For dry beans the sequence is fixed and easy to read. Leaves yellow from the bottom of the plant upwards and drop, until the plant is a bare framework hung with pods. The pods go from green through yellow to a dull tan or gray-brown, and the walls turn papery. About 95 per cent of the pods should reach that state before you cut.

Then test the beans. Shaken, the pods should rattle. Opened, the beans should be hard, glossy black and loose in the pod, and a thumbnail pressed firmly into one should leave no dent. If your nail marks the bean it is still too soft to cut.

You cannot simply leave the plants standing until everything is bone dry, because the pod walls build tension as they dry and eventually the seams snap apart and throw the beans several feet across the bed. The large pods of a black-seeded type hold on slightly longer than an ordinary soybean's, but they shatter just as completely once they start, and because this crop dries down in autumn, the trigger is usually a spell of rain followed by hot sun.

The deadline is therefore hard. Once you find the first two or three split pods anywhere in the block, cut it within twenty-four hours. Shattering does not creep through a crop; it goes from nothing to widespread over a couple of days.

Cutting and finishing the dry crop

Work on a dry morning after the dew has burned off and before the afternoon heat. Damp pods will not shatter, which sounds convenient, but beans cut damp have to be dried harder and longer and any mold starting in the pile is worse than a handful of lost beans. Dry pods and gentle hands is the right balance.

Cut the stems at soil level with pruners rather than pulling the plants. Cutting leaves the nitrogen-bearing root nodules in the bed to break down, keeps soil out of the pods, and on a plant this size is far easier than wrestling a taproot out of the ground. Lay each plant straight into a tub or onto a sheet as you cut it.

The crop is not finished when it comes out of the bed. Move the cut plants the same day to a covered, airy, shaded space and hang them upside down in loose bundles of four or five, or spread them one layer deep on a sheet, with something underneath to catch beans from pods that split as they dry. Two to three weeks is typical.

The beans are ready to store only when they shatter rather than dent. Bite one, or tap one with a hammer: a properly dry bean cracks into fragments, an underdried one flattens. Then thresh in a closed sack, winnow in a breeze, sort out anything holed, split or shriveled, and store in airtight jars somewhere cool and dark. Note that the dark seed coat colors cooking water deeply, which is normal and not a sign of anything wrong.

1. Cut at soil level on a dry morning Pruners, stems cut cleanly, roots left in the bed. Lay each plant straight into a tub so that pods splitting as you work drop their beans where you can find them.
2. Hang or spread the same day Loose bundles of four or five hung upside down, or one layer on a sheet in a shed with the door open. A heap left overnight heats and then molds.
3. Test before threshing A dry bean shatters under a hammer and hurts your teeth if you bite it. One that flattens or dents goes back for another week.
4. Thresh, winnow and sort Tread the plants in a closed sack, pour between buckets in a breeze, then hand-sort. Discard holed, cracked or shriveled beans before they reach the jar.

Raw soybeans of any color must not be eaten. Soak overnight, discard the water, and boil hard in fresh water for at least an hour, often closer to two, until a bean crushes easily between finger and thumb.

What to write down at harvest

The two harvest dates are the most valuable numbers this crop produces. Record the date the first flowers opened, the date you picked green or cut the block, and the number of days between them. On a long-season crop those days vary far more with the autumn you get than the seed packet suggests, and your own figure is the only one worth planning against.

Record whether any pods had split before you cut. That single line tells you whether you left it too fine and should be cutting three days earlier next year, which is the most common and most expensive timing error on this crop.

Weigh the finished dry beans and note the weight against the area the block occupied. A black soybean takes up two to three times the space per plant of an ordinary soybean, so the honest question is yield per square foot, and it is easy to measure exactly once the beans are in a jar.

Keep a labeled jar of seed from your best plants, separate from the eating beans, and never from any plant that showed mottled or puckered leaves. Note the year on it: germination falls away noticeably after two years, faster than most vegetable seed.