The short answer: beans and peas grow well in coco coir, but don't expect them to feed themselves. In a fertigated soilless substrate the nitrogen in your feed suppresses nodulation, so treat them like any other fruiting crop and give them a complete feed. Climbing beans want a container at least 75 cm wide and 45 cm deep, peas at least 45 cm wide, and both need the support in place before they start to climb.
Key facts
- With full nitrogen in the feed, inoculated beans formed small nodules and fixed no nitrogen. Cutting nitrogen to a third gave working nodules, but also smaller plants.
- Common bean nodulates poorly in pure solution culture. A solid substrate does better than water alone.
- Peas and beans need different rhizobia. A pea inoculant won't nodulate runner or French beans.
- Pea shoots are ready in 3–4 weeks at 10–15 cm from a garden sowing, or 10–14 days in dense commercial trays.
Why coir works for legumes
Beans and peas hate two things: cold, wet roots at sowing and a dry root zone at flowering. Coir handles both. It drains freely enough that big seeds don't sit in water and rot, and it holds enough between waterings to carry a plant through a hot afternoon in flower.
It's also light. A 75 cm trough of coir for climbing beans on a balcony or roof weighs a fraction of the same trough of soil. That's why it's the usual base for terrace and rooftop gardens.
Washed coir is not buffered. In the first weeks it takes up calcium and magnesium from your feed. Charge it with a full calcium-containing feed before you sow, then feed normally.
The nodule question
Legumes swap sugar for nitrogen with rhizobia living in root nodules. In soil, a well-nodulated bean or pea needs little or no nitrogen fertiliser. Most growers assume the same will happen in coir. It usually doesn't, for three reasons.
- There are no rhizobia to start with. Fresh coir from a factory is not soil. Unless you add an inoculant, there may be nothing in the bag to form nodules.
- Nitrogen in the feed switches nodulation off. When beans got full-strength nitrogen in their feed, inoculated plants formed markedly smaller nodules and fixed no measurable nitrogen. At a third of normal nitrogen, or none, the plants nodulated and fixed nitrogen, but shoot growth was lower than with full feed. Ammonium-fed plants in substrate culture formed no nodules at all, whatever the concentration.
- Wet, airless root zones don't suit nodules. Common bean nodulates poorly in pure solution culture, which is why researchers growing beans hydroponically for nodule work have recommended a solid substrate such as gravel. Coir is better than water alone, but only if it isn't kept waterlogged.
So what should you do? For a crop you want to pick, feed the plants fully and forget about nodules. You'll get more pods. If you want to grow with less nitrogen, for an organic system or for a school or research setup, inoculate the seed and cut nitrogen. Don't expect the same growth as a fully fed crop.
Buy the right inoculant. Peas, vetch and lentils share one group of rhizobia. Garden beans, French beans, kidney beans and scarlet runner beans need a different one. A pea inoculant won't do anything for your beans.
Containers and spacing
| Crop | Minimum container | Plants | Support |
|---|---|---|---|
| Dwarf French bean, bush bean | 30–45 cm wide, at least 19 litres and 20–30 cm deep | Seeds 15 cm apart | None, or short twigs |
| Climbing French bean, runner bean | 75 cm wide, 45 cm deep | Two seeds at each cane, canes 15–30 cm apart | Canes or strings to 2.5 m |
| Dwarf pea | 7.5 litres and 10–15 cm deep as a bare minimum, 45 cm wide is better | 7.5 cm apart | Twiggy sticks, plants reach about 45 cm |
| Tall pea, snow pea, sugar snap | 45 cm wide | 7.5 cm apart | Netting or sticks to 1.8 m |
| Pea shoots | Shallow tray | 2.5 cm apart in a garden tray, or broadcast thickly in a commercial tray | None |
You'll see anything from 7.5 litres to 19 litres quoted for a single bean or pea plant. The smaller figure keeps a dwarf pea alive. The larger one gives a bean plant enough water reserve to get through a hot day in flower, which is when pods are set or lost. If you're choosing between a deep narrow pot and a wide shallow one, go wide for peas and beans. Their roots spread more than they dive.
Coir grow bags laid flat with two or three planting holes make a good base for a row of climbing beans against a wall. Push the canes through the bag into the ground or tie them to a frame, because a full crop of runner beans in wind will pull a free-standing cane over.
Sowing in coir
- Sow 5 cm deep. Beans and peas both go in at that depth in pots and modules.
- Wait for warmth. Beans need the substrate above 12 °C to germinate reliably. Peas will go in at 10 °C.
- Moist, not wet. Big legume seeds rot in cold, saturated substrate. Water the coir first, let it drain, sow, and don't water again until you see the first shoots unless the surface is drying out.
- Modules first if slugs or mice are a problem. Sow one seed per module or three per small pot and plant out at about 20 cm tall for peas, after the last frost for beans.
Feeding and watering
Feed from planting at a normal vegetable strength, then keep going. Garden guidance is to feed beans and peas in containers every two weeks once the first flowers open. In coir you're better off feeding at every watering at a lower rate, because the coir holds little in reserve.
Water matters most at flowering. Hot weather and dry spells cut pod set in runner beans, and peas give a better crop when watered thoroughly as they start to flower and again two weeks later. In a container that means checking every day once flowers open, and twice a day in a heatwave.
Keep water off the leaves where you can. Powdery mildew on peas is worst on plants that are dry at the root and crowded at the top.
Picking
| Crop | Pick at | How often |
|---|---|---|
| Runner bean | 20–25 cm pods | Every 2–3 days. Cropping lasts eight weeks or more |
| French bean | Pods snap cleanly, seeds not yet bulging | Every 2–3 days |
| Mangetout, snow pea | About 7.5 cm, before peas show | Every 2–3 days |
| Sugar snap | Pods plump but still crisp | Every 2–3 days |
| Shelling pea | Pods full and bright green | Every few days from the bottom of the plant up |
Picking often is the single biggest yield factor. A bean plant that's allowed to ripen seed slows down or stops flowering.
Pea shoots in coir
Pea shoots are the one legume crop where coir goes into trays rather than pots. There are two ways to grow them.
Garden-style shoots. Sow peas 2.5 cm deep and 2.5 cm apart in a tray of moist coir. Cut at 10–15 cm, about 3–4 weeks after sowing, leaving 2.5 cm of stem so the plants regrow for a second cut.
Commercial tray shoots. Soak seed before sowing. Published soak times run from about 6 hours to overnight, and 8–12 hours is the common middle. Spread 140–280 g of seed across a 25 × 50 cm tray on a thin layer of moist coir, cover or stack for a few days of blackout, then bring into light. Cut at 8–15 cm, 10–14 days from sowing, with scissors just above the coir.
Large pea seeds are prone to mould in a dense tray. Keep airflow up, water from below, and don't over-soak the seed. Peas are also the one microgreen where coir alone has trailed a peat-perlite mix on yield, so read our article on coco coir for microgreens before you commit a whole shoot operation to straight coir.
Problems and causes
| Problem | Likely cause | Fix |
|---|---|---|
| Seeds rot before emerging | Cold, saturated substrate | Sow into drained coir, wait for 10–12 °C |
| Pale, yellowing plants | Too little nitrogen. No nodules to make up for it | Feed fully with nitrogen in the mix |
| Flowers drop, no pods (runner beans) | Hot, dry root zone at flowering | Water every day once flowering, more volume per plant |
| Powdery mildew (peas) | Dry roots, crowded plants, late sowing | Steady watering, space plants, water the base |
| Plants collapse at soil line | Root or collar rot from waterlogging | Better drainage, fewer, smaller waterings |
| Mould in shoot trays | Seed too dense, poor airflow, over-soaking | Thinner sowing, bottom watering, a fan |
Coir for your bean and pea crop
CVM Fiber and Industries in Kanyakumari, Tamil Nadu, India, makes washed coco peat in 5 kg blocks and 650 g briquettes, plus grow bags, open-top slabs, husk chips and custom blends. The peat is washed with water to reduce EC, with no calcium nitrate or other chemicals added. Briquettes suit pea shoot trays and small pots. Blocks and grow bags suit rows of climbing beans. If you'd like to talk about which format fits your crop, contact us.
FAQ
Do beans fix their own nitrogen in coco coir?
Usually not. Fresh coir has no rhizobia unless you add an inoculant, and nitrogen in the feed suppresses nodulation even when you do. For a crop you want to pick, give beans a complete feed with nitrogen. Only cut nitrogen if you've inoculated and accept slower growth.
Can I use the same inoculant for peas and beans?
No. Peas, vetch and lentils share one group of rhizobia, and garden beans, French beans and runner beans need a different group. Buy the inoculant that matches the crop you're sowing.
What size pot do climbing beans need?
For runner beans and climbing French beans, a container at least 75 cm wide and 45 cm deep, with canes or strings up to about 2.5 m. Dwarf beans manage in 30–45 cm wide pots. Smaller containers dry out too quickly when the plants are flowering.
Can peas grow in pure coco coir?
Yes. Peas grow well in straight coir in containers at least 45 cm wide, sown 5 cm deep and 7.5 cm apart. Feed from planting and water thoroughly when flowering starts. Tall varieties need netting or sticks up to 1.8 m.
Why are my runner bean flowers falling off?
Hot weather and a dry root zone at flowering are the usual causes, and containers dry out fast. Water every day once the plants flower, twice a day in a heatwave, and use a bigger container next year. Poor set early in the season is also common and usually improves.
How long do pea shoots take in coir?
About 10–14 days in a dense commercial tray, cut at 8–15 cm. A garden sowing at 2.5 cm spacing takes 3–4 weeks to reach 10–15 cm, and if you cut 2.5 cm above the base it will regrow for a second harvest.
Should I soak pea seeds before sowing in coir?
For shoot trays, yes. Most growers soak for 8–12 hours, though anything from about 6 hours to overnight is used. For peas sown in pots for a pod crop, soaking isn't needed.