Feeding a plant that makes its own nitrogen
Run beans at a noticeably lower nitrogen level than a leafy crop. Standard hydroponic A/B formulations assume the plant cannot fix nitrogen; for beans that means too much of it, and the result is a huge leafy plant with very few pods.
Practically: keep EC at 1.4–1.8 and pH 6.0–6.5. If you have a choice of formulations, the bloom or fruiting mix suits beans better than the vegetative one, even during early growth. A nitrogen-deficient-looking bean is usually a healthy one.
In a fresh DWC system with no soil there are no rhizobia to begin with. Nodulation may not develop at all, in which case the plant relies entirely on the solution — so do not starve it. Aim for adequate, not generous.
Bush or climbing
Bush beans grow 40–60 cm (16–24 in), crop over three or four weeks and stop. They suit a bucket exactly: compact, no support needed, and the whole harvest lands in a predictable window.
Climbing (pole) beans run to two metres (6.6 ft) or more, crop over a much longer period, and yield more per plant — but they need a support structure and they will outgrow a small reservoir's ability to keep up with water demand. In a 10 L bucket, expect to top up daily at peak.
For a countertop system, bush varieties are the sane choice. The catalogue lists plant height for every variety — filter on that first.
Sowing and germination
Bean seeds are large and germinate reliably in 5–10 days at 18–22 °C (64–72 °F). Sow direct into the net pot, about 3 cm (1.2 in) deep, one seed per pot. Do not pre-soak unless the seed is old — beans left in water too long split and rot.
The seedlings are vigorous and push up fast. Keep the reservoir level a little lower than usual until the first true leaves appear, so the cotyledons do not sit wet and mould.
Beans resent root disturbance more than most crops, which is another argument for sowing direct rather than transplanting.
Harvesting: green or dry
You can eat beans at three stages and each needs different timing. As green beans, pick young and often — the plant responds to regular picking by setting more pods. As shelling beans, leave the pods until the beans inside are full but still soft. As dry seed, leave them on the plant until the pods rattle.
If you want seed, stop picking green. A plant that is continually harvested for green pods will keep producing them and never commit to maturity. Choose one or two plants at the start of the season and leave them alone entirely.
Saving seed: the easy one
Beans are self-pollinating — the flower fertilises itself before it opens — so crossing is rare and isolation of 3–5 metres (9.8–16 ft) is plenty. Even that is only needed if you are growing several varieties of the same species close together.
Let the pods dry on the plant until they are brown and the seeds rattle. If rain threatens, pull the whole plant and hang it upside down indoors to finish drying. Shell the pods by hand, discard any seed with a hole in it (bean weevil), and dry the seed further on a plate for a week before storing.
Properly dried bean seed keeps for four to six years in a sealed jar with a desiccant, in the fridge. It is the most forgiving seed in this catalogue to store.
What goes wrong
Flowers drop without setting pods. Almost always temperature — above 30 °C (86 °F) or below 15 °C (59 °F) at flowering. Beans are fussier about this than tomatoes.
Huge plant, no pods. Too much nitrogen. Drop the EC and check you are not running a vegetative formulation.
Yellowing leaves from the bottom up. Could be nitrogen deficiency in a plant that failed to nodulate, or waterlogging. Check the roots: white and firm is healthy, brown and slimy is rot.
Beetles eating holes in pods. In an indoor system it is usually bean weevil emerging from stored seed rather than a field pest — inspect your seed stock before sowing.