Part IV · Grow
Pea shoots, tips and mistakes to avoid: growing legumes successfully in hydroponics
Functional diagram, not to scale.
The pea shoot tutorial in two to three weeks, twenty tips for generous beans and peas, and the table of common problems: dropping flowers, black aphids, powdery mildew, empty pods.
The last article in the series: the tutorial for pea shoots, the quickest way to taste hydroponic legumes, followed by our tips and the mistakes to avoid for generous beans and peas.
1. Pea shoots: the ideal first try
Young pea stems, tender and sweet, are eaten raw in salads or sautéed for a minute. The University of Minnesota also notes that the tender tips of pea stems are edible. Grown densely on a tray, they are ready in two to three weeks.
Pea shoots on a tray
- Choose the seedsPeas sold for shoots, or untreated field peas. Never seeds coated with fungicide.
- Soak8 to 12 hours in cool water; the seeds double in size. Rinse.
- Sow denselyOn a tray lined with a growing mat, a rockwool slab or a little coco coir, in a single dense layer.
- Darkness for 2 to 3 daysCover with a second tray or a piece of cardboard, and keep moist by misting or adding a little water to the bottom.
- LightAs soon as the shoots lift the cover, place them under the LED or near a window. Water from below with a very dilute solution.
- HarvestAt 10 to 15 cm (4 to 6 in), with scissors, above the first node: some varieties regrow for a second cut.
2. Twenty tips for generous harvests
- Beans in the warmth, peas in the cool: respecting their season is half the battle.
- Direct sowing in the final net pot or bucket: no transplanting.
- Lukewarm growing medium for beans: in the cold, the seeds rot.
- Whole seeds: discard split seeds.
- Short soak: a few hours, no more than one night.
- Support from sowing day: string for pole beans, netting for peas.
- Help the first twist of climbing beans around the string.
- Bush types for small spaces: tub, tower with large pots, very bright windowsill.
- Plenty of light: pods fill out with light.
- A gentle fan: helps pollination and limits powdery mildew.
- Light solution at first, then around 2.0 to 2.5 at flowering; pH around 6 (Oklahoma State).
- No excess nitrogen: it makes leaves, not pods.
- “Bloom” fertilizer from the first flowers.
- Steady watering during flowering: one dry spell makes the flowers drop.
- Shade during heat waves: strong heat day and night means aborted flowers.
- Pick every 2 to 3 days: the plant keeps flowering.
- Pick tender: before the beans inside make green beans bumpy.
- Pinch the tops of fava beans at flowering: fewer black aphids, better-filled pods.
- Staggered sowings of bush beans every 3 weeks to spread out the harvest.
- Save seeds from your best open-pollinated varieties, and share them at the seed swap.
3. Common problems
| Symptom | Likely causes | What to do |
|---|---|---|
| Seeds rot without sprouting | Growing medium too cold or too wet, split seeds | Warm it up, water less, sow whole seeds. |
| Flowers drop without pods | Excessive heat day and night, water stress, excess nitrogen | Shade, steady watering, “bloom” fertilizer. |
| Peas stop producing | Heat, above roughly 29 °C (84 °F) | Grow in spring, in fall or in a cool room. |
| Black colonies at stem tips | Black aphids (mostly on fava beans) | Pinch out the tops, spray of water, diluted black soap, ladybugs. |
| White powder on the leaves | Powdery mildew (mostly peas, late in the season) | Ventilate, remove affected leaves, avoid stale air. |
| Fine webs, speckled leaves | Spider mites, hot dry air | Mist, shower, isolate. |
| Short, poorly filled pods | Lack of light, heat, picking too far apart | More light, frequent picking. |
| Stringy beans | Picked too late | Pick every 2 to 3 days, younger. |
| Brown roots, bad smell | Warm solution, lack of oxygen | Solution around 20 to 24 °C (68 to 75 °F), aeration, cleaning. |
The full diagnostic method is in Diagnosing: think before you correct. Questions? The forum is waiting for you.
Frequently asked questions
How do you grow pea shoots?
Soak peas (a shoot variety or untreated field peas) for 8 to 12 hours, spread them densely on a tray lined with a growing mat or a little coco coir, cover them for 2 to 3 days in the dark while keeping them moist, then move them into the light. Harvest with scissors when the shoots are 10 to 15 cm (4 to 6 in) tall, above the first node.
Why do my beans flower without making pods?
Most often because of heat: the University of Minnesota points out that very hot days and nights make the flowers abort. Water stress, excess nitrogen or a lack of light also play a part. Provide shade during heat waves, keep watering steady and switch to a “bloom” fertilizer.
- University of Minnesota Extension, Growing beans in home gardens
- University of Minnesota Extension, Growing peas in home gardens
- Oklahoma State University Extension, Electrical Conductivity and pH Guide for Hydroponics (HLA-6722)
- Karavidas et al., Hydroponic Common-Bean Performance under Reduced N-Supply Level and Rhizobia Application, Plants, 2023
