The short answer: coco coir works in a vertical farm in three places. As a propagation plug or net-pot fill for lettuce and herbs that finish in NFT, rafts or ebb-and-flow. As a thin mat or loose bed for microgreens. And as the full root zone for crops that need one, mainly strawberries, basil and cut-and-come-again herbs in pots or troughs on racks. It loses to rockwool and phenolic foam on dimensional uniformity straight off a seeding line. It wins on root-zone air, a medium less conducive to Pythium when wet, and a spent plug that goes on the compost heap instead of into a skip.
This article is about what changes when the farm is a sealed, stacked, artificially lit room with recirculating water and a seeding machine. The crop detail lives in coir for lettuce and leafy greens, coir for microgreens and coir discs and propagation plugs.
Where coir fits, system by system
Most plants in a vertical farm never get a root zone of their own. A lettuce spends 10 to 14 days in a plug and another three to four weeks with its roots in water. So the first question isn't "coir or rockwool" but "what job does the substrate do here, and for how long".
| System | What the substrate does | How long it matters | Coir's role |
|---|---|---|---|
| NFT channels | Anchors the seedling, holds water until roots reach the film | Plug stage plus the first week | Bound plug or 25 to 40 mm net-pot fill. Must not shed fines |
| DWC rafts | Anchors the plant, wicks water to the crown early | Same | Plug or net-pot fill. Wicking helps on day one, hurts if the plug sits in water later |
| Ebb-and-flow benches | Full root zone, flooded several times a day | Whole crop | Loose coir in pots or cells. Fewer floods than perlite |
| Aeroponic towers | Holds a plug in a collar | Plug stage | Plug must survive repeated wetting and drying |
| Drip-fed pots and troughs (strawberries, basil, chard) | Full root zone | Whole crop, often months | Coir or coir-and-chips in 1 to 3 litre pots or slim troughs |
| Microgreen trays | A 1 to 2 cm bed for 7 to 21 days | Whole crop | Fine loose coir or a needled coir mat |
Ebb-and-flow and drip-fed pots are coir's natural home. In an NFT trial with pak choy, plants on coco peat reached an average fresh weight of 167 g at 30 days against 93 g on rockwool, with taller plants and more leaves from the first week. In stacked-pot towers, pure coconut fibre gave the heaviest first crop of lettuce against perlite and bark.
The plug stage is more contested. In a raft trial of 13 plug substrates over three seasons, a 75 % peat and 25 % fine coir mix produced the heaviest lettuce and rocket, and peat-based plugs beat both pure coir and the inorganic plugs. A raft plug has one job for two weeks, and a fine, firm, slightly acidic plug does it well. That's the honest picture: coir is strongest where it holds the roots for the whole crop, and competitive but not dominant as a short-lived plug.
Coir plugs vs rockwool vs foam vs peat
A vertical farm asks three things of a plug: does it seed evenly on the line, does every cell behave the same, and does it keep roots oxygenated in a wet environment?
| Property | Coir plug | Rockwool plug | Phenolic foam plug | Peat plug |
|---|---|---|---|---|
| What it is | Compressed pith, with a biodegradable net or binder | Spun basalt fibre, bonded, pre-drilled | Open-cell synthetic foam, pre-dibbled | Compressed peat in a net |
| Water at saturation | 73 to 80 % by volume in loose pith | About 87 % | 91 to 93 % | About 65 % |
| Air at saturation | 9.5 to 12.6 % in loose pith | About 5 % | 5 to 7 % | About 11 % |
| Water release | Gradual | Drops sharply, dries abruptly | As rockwool | Gradual, but repels water once dry |
| pH as supplied | 5.6 to 6.9 | High. Soak at low pH first | Near neutral, inert | 5.3 to 5.5 |
| EC as supplied | Low if washed, variable if not | Zero | Zero | Depends on fertiliser charge |
| Cation exchange | Moderate | None | None | High |
| Dimensional uniformity | Good for bound plugs, poor for loose discs | Very high | Very high | Good |
| Shipping | Dry, compressed | Bulky, pre-formed | Bulky, pre-formed | Dry, compressed |
| After harvest | Compostable | Landfill or specialist recycling | Landfill | Compostable |
The two inert media hold the most water and the least air, and because that water sits loose in the pores rather than inside the particles, they go from soaked to dry quickly. That's why rockwool on an ebb-and-flow bench needs more frequent floods than coir, and why a stone wool cube needs less water and fertiliser per cycle: it simply holds less. Coir and peat hold a few more percent of air, release water gradually and buffer the root zone against a missed irrigation. Peat turns hydrophobic when it dries right out. Coir rewets readily, which matters when a tray sits uncovered under lights for a day.
Cell height matters as much as material. Air-filled porosity in the same medium falls from around 19 % in a 15 cm pot to under 1 % in a 1.3 cm plug cell. In a wet plug tray every medium is short of air, and the one that keeps a few percent more pores open has the edge. The full-crop comparison is in coco coir vs rockwool.
Dissolved oxygen in the pond is a separate matter. Lettuce grows well at 4 mg/L and above and ponds are usually held at 7 to 10 mg/L with injected oxygen. The plug has no say in that. What it controls is whether roots in the first two weeks sit in a waterlogged block, so set the raft hole or net pot so the plug bottom touches solution and the body sits above it.
Cleanliness and pathogens in a sealed room
A vertical farm has no soil, no rain and no insects coming through vents, so whatever goes wrong in the root zone came in on a plant, a plug or the water.
Rockwool and foam arrive with nothing living in them. Coir doesn't. It is dried and compressed, not sterilised, and a bale stored damp can carry moulds and the odd gnat larva. The detail is in is coco coir sterile? In short, clean coir from a dry, covered line is low-risk, and full sterilisation usually backfires because it removes the harmless microbes that would otherwise occupy the surface.
Once the crop is in, the picture flips. In a cucumber trial on 7 cm slabs, rockwool was more conducive to Pythium root and crown rot than coir dust, pumice or perlite, and the higher disease level tracked with rockwool's much higher water content. Doubling the slab to 14 cm, which drops the water content, greatly reduced disease on rockwool. Pythium zoospores swim. The wetter the medium, the faster they move.
Fungus gnats get blamed on coir, and the evidence doesn't support singling it out. A generation takes 20 to 28 days, adults live 7 to 10 days and lay 100 to 200 eggs, and larvae feed in the top 2.5 to 5 cm of moist medium. Survival peaks at roughly 52 % moisture and falls off in very wet and very dry media. Gnats survive and reproduce just as well in a coir-based mix as in a peat-based one. What drives them is standing water, algae on tray surfaces and media that never dry, all of which a vertical farm can control. Sticky cards, letting the top 2 to 3 cm dry between irrigations, Steinernema feltiae nematodes, Bti drenches and the predatory mite Stratiolaelaps scimitus work the same in coir as in anything else.
Automated seeding lines: what coir has to get right
This is where rockwool and foam earned their place. A stone wool sheet holds 200 pre-drilled plugs in a 10 by 20 grid, every hole the same depth, and goes under a drum or vacuum seeder and straight to the germination bench. Foam comes in 72, 105 and 128-cell trays with a 1 cm dibble pressed in and a plug body about 2.5 to 3 cm square by 4 cm deep. Nursery automation was built around that uniformity, and earlier coir blocks varied enough in size that growers gave up on them.
Bound coir plugs have closed most of the gap. Three routes:
- Net-bound plugs. Compressed coir or coir-peat inside a fine net, PLA (compostable) or synthetic. The plug swells on wetting, so the wetted dimension is what you specify.
- Binder-stabilised plugs. Loose coir mixed with a binder and moulded. Older binders were urea-formaldehyde or latex based. Newer plugs use bio-based binders so the whole plug composts. Ask what the binder is, whether it's certified compostable, and whether it's accepted under the organic rules you grow to.
- Open-net holders filled with loose coir. A biodegradable polymer net dropped into trays by a dispenser at 10,000 to 50,000 an hour, then filled by the tray filler with the mix you choose. The net keeps a fine washed coir together in the raft.
Whichever route, specify four things for the line:
- Particle size. Fine pith with the coarse fibre screened out for plugs and microgreen beds. A pith-and-chip blend for pots and troughs. Fines that wash out of a plug end up in filters and emitters.
- Wettability. Dry compressed coir must take water evenly from the first flood or the seed sits in a dry pocket. Run a tray through your own first-wetting routine before you order a container.
- EC and pH as supplied. Washed coir arrives with low, stable EC and pH in the high fives to mid sixes, which suits lettuce, herbs and strawberries without adjustment. Unwashed coir doesn't. Coir's cation exchange means drain EC won't track feed EC as tightly as with rockwool in the first weeks, so feed on measured drain, not the recipe.
- Dimensions after wetting. Diameter, height and expansion, so the swollen plug fits your raft hole, net pot or collar. A plug 2 mm too wide jams a transplanter.
Disposal, weight and waste
A vertical farm throws away a plug for every plant it sells. One commercial raft operation grows around 2 million lettuce and pak choi a year on one hectare. That's 2 million plugs. Stone wool recycling schemes exist, but published rates range from about 45 % to 65 % depending on who counts and where, and the rest goes to landfill. Foam is synthetic and goes to landfill or industrial composting. Coir and peat plugs with a compostable net or binder can be composted on site or collected with crop trimmings, and in multi-year European trials peat-free mixes built around coconut fibre matched rock wool and peat on yield while being far easier to reuse or compost afterwards.
Coir ships compressed and expands with water you already have on site. Rockwool and foam ship at full volume. Cost per plug is harder to call: bound coir plugs cost more than a brick of loose coir and often as much as foam, and the saving comes from freight, storage and disposal rather than the unit price. Price it as a system.
What a vertical farm should specify when ordering
For loose coir (microgreen beds, ebb-and-flow pots, troughs):
- Washed, with the supplier's typical EC and pH range stated, and your own test on arrival.
- Particle grade: fine pith for trays, pith with 20 to 30 % husk chips for pots carrying a crop for months.
- Low fibre content so trays spread evenly and don't mat.
- A compressed format that suits your line. A 650 g briquette hydrates in a bucket for a tray batch. A 5 kg block feeds a mixer.
- Dry, covered storage at both ends.
For plugs:
- Dry and wetted dimensions, and expansion ratio.
- Net or binder material, with compostability status in writing.
- Buffered or unbuffered, and whether it carries a starter charge.
- A sample tray run through your seeder, germination room and raft before you commit.
We make washed, unbuffered coco peat in Kanyakumari, Tamil Nadu, India, in 5 kg blocks, 650 g briquettes and custom blends of pith and husk chips. If you want a fine grade for trays, a chip blend for troughs, or a specific particle cut for a plug maker, get in touch with your tray format, system type and crop, and we'll put a sample together.
FAQ
Is coco coir good for vertical farming?
Yes, in the right place. It does well as the full root zone in ebb-and-flow pots, drip-fed troughs and microgreen trays, where it has matched or beaten rockwool and perlite in lettuce and pak choy trials. As a short-lived raft or NFT plug it is competitive rather than dominant, and you need bound plugs if you seed by machine.
Can I use coco coir plugs in NFT and DWC?
Yes, as long as the plug holds together when wet and doesn't shed fines into the channel or pond. Use a net-bound or binder-stabilised plug, not a loose disc. Set the raft hole or net pot so the plug bottom touches the solution and the body sits above it, or the plug stays waterlogged.
Coco coir or rockwool for an indoor leafy greens farm?
Rockwool gives very uniform plugs that run through any seeder and arrive clean. Coir gives more air, gradual water release, a medium less conducive to Pythium when wet, and a compostable spent plug. If your line is built around stone wool and your waste is recycled, stay with it. If disposal is costly or you grow to organic rules, trial bound coir plugs.
Do coir plugs cause fungus gnats in a vertical farm?
Not more than any other organic medium. Gnats breed in media at around 50 percent moisture with algae or decaying matter to feed on, and survive equally well in coir-based and peat-based mixes. Let tray surfaces dry between irrigations, remove algae and dead leaves, hang sticky cards, and use nematodes or Bti if adults appear.
Is coco coir sterile enough for a sealed grow room?
No plant-based medium is sterile, and coir isn't sold as such. Clean coir that has been washed, dried and stored under cover is low-risk. Rockwool and foam arrive sterile but are no cleaner once the crop is in and the water is recirculating.
What EC and pH should coir have for lettuce and herbs?
Washed coir typically arrives with a low EC and a pH between about 5.6 and 6.9, which suits lettuce, basil and most herbs. Feed lettuce at roughly 1.2 mS/cm above source water at pH 5.6 to 6.0, and manage on measured drain, because coir's cation exchange shifts the numbers a little in the first weeks.
Can spent coir plugs be composted?
The coir can. Whether the whole plug can depends on the net or binder. PLA nets and bio-based binders compost, synthetic mesh and older resin binders don't. Get the compostability status in writing and check your local composter accepts it.
Are coir plugs cheaper than rockwool or foam plugs?
Per plug, often not. Bound coir plugs cost more to make than loose coir and about the same as, or more than, foam. The saving is in freight and storage, because coir ships compressed, and in disposal, because the spent plug composts instead of going to landfill. Compare the whole system cost.