Coco coir works in both, but it behaves differently. In a fabric pot the walls breathe, so coir dries faster, stays cooler in sun and grows a fibrous, non-circling root system through air pruning. In a plastic pot it holds water longer, needs watering less often and is easier to run on a tight fertigation schedule. Fabric suits growers who can water often and want the best roots. Plastic suits anyone who can't be there every day or is paying for every litre of water.
What actually differs between the two pots
| Fabric pot with coir | Plastic pot with coir | |
|---|---|---|
| Water loss | Through the surface, the base and the walls | Through the surface and drain holes only |
| Watering frequency | Higher, often daily or more in warm weather | Lower for the same plant and pot size |
| Root-zone temperature in sun | Lower, because the wall evaporates water | Higher, especially in black plastic |
| Root shape | Roots stop at the wall and branch | Roots reach the wall and circle |
| Salt deposits | On the outside of the fabric and the media near the wall | Mostly in the top layer and around drain holes |
| Algae | Green bottom edge is common | Inside translucent pots, not opaque ones |
| Weight when dry | Very light, easy to tip | Light, a little more stable |
| Life | A few seasons, then fabric wears | Many seasons |
Air pruning: why roots look different
When a root tip grows into a fabric wall, it meets dry air and stops extending. The plant responds by branching further back along that root. The result is a dense web of fine roots throughout the pot rather than a few thick roots wrapped around the outside.
In a smooth plastic pot, roots that reach the wall turn and keep growing along it. That's root circling, and in nursery stock it can carry on after planting out. In a trial on shrub roses, fabric containers cut root deflection and circling about fivefold compared with conventional black plastic, and the roses grew better shoots in both a peat-based and a bark-based substrate.
Coir gets along with air pruning well because it holds plenty of air even when wet. Roots grow right out to the wall rather than dying back from a waterlogged edge. The trade-off is that the outer centimetre or two of coir dries fastest, so those wall roots need regular water.
Drying speed and watering frequency
Coir at container capacity holds roughly 60 to 80% of its volume as water. In plastic, that water leaves through the plant and the surface. In fabric, it also wicks into the wall and evaporates from the whole outside of the pot.
The difference is large. Side by side with the same moist mix and no plants, a porous fabric pot can lose roughly twice as much water through evaporation over a warm day as black plastic, before the plant takes any up at all.
What that means day to day with coir:
- Expect to water more often in fabric. In warm weather, small fabric pots can need water more than once a day. Plastic pots of the same size might go a day or two.
- Lift the pot to judge it. A drained pot of coir is heavy and a dry one is surprisingly light. Learn both weights and you'll stop guessing.
- Don't let coir dry right out. Bone-dry coir sheds water at first and takes several slow passes to rewet. In fabric that happens quickly on a hot, windy day. If it does, see rewetting dry coco coir.
- Size up if you can't water often. A bigger fabric pot buffers the drying, at the cost of more media.
- Use drippers or a saucer. Several small drips through the day suit coir in fabric far better than one big soak.
If you run fertigation to waste in plastic, the same program usually needs more, smaller irrigations in fabric to hold the root zone steady.
Heat: where fabric really earns its keep
Black plastic in full sun gets hot. Measurements on the sun-exposed side of black containers have reached 46°C and, in Oklahoma, a maximum of 56°C, with no roots at all in about a third of the container volume on that side. Painting or co-extruding white on the outside helped by only a few degrees.
Fabric pots cool by evaporation through the wall. On hot, sunny days the root zone in fabric can run many degrees cooler than in black plastic, which soaks up heat. That can be the difference between roots working and roots cooking.
Coir adds a second cooling effect of its own: it's light-coloured and holds a lot of water, and wet media change temperature slowly. But it can't do much against a black plastic wall in direct sun. If you have to use plastic outdoors, shade the pot sides, use white or light-coloured pots, or group pots so they shade each other. More on managing heat around the roots in our guide to root-zone temperature in coco coir slabs.
The same evaporation that cools fabric pots in summer works against you in a cold spring or an unheated tunnel. Plastic holds root-zone warmth better in cool weather.
Salt and nutrients at the wall
Coir is usually fed at every irrigation, so salts are always arriving. When water evaporates through a fabric wall, the dissolved salts stay behind. In porous fabric containers the media just inside the wall ends up far saltier than the media in the middle of the pot. The fabric itself turns grey-white with a crust of fertiliser and water salts.
In practice:
- Run a little drainage at most irrigations so salts leave through the base rather than piling up at the wall.
- Flush periodically with plain water if the outside of the fabric goes crusty or the plant's edge roots look burnt. The method is in how to flush coco coir.
- Measure EC from the drain, not the wall. Squeezing media from the edge of a fabric pot will read high.
Plastic pots aren't free of salt build-up, but it collects at the top surface and around drain holes rather than all the way round.
Which pot for which grower
Choose fabric if you water at least daily or have drip irrigation, you grow in heat or full sun, you're raising plants that will be moved or planted out and you want strong, non-circling roots, or you grow large plants where root quality pays back.
Choose plastic if you're away for days at a time, water is expensive or restricted, you grow in a cool spring tunnel, you're running a precise recirculating fertigation system where you don't want the wall changing the numbers, or you want pots that last for years.
Mixed approaches work too. Some growers use fabric for the outdoor summer crop and plastic for indoor or early-season work. Others set fabric pots in a shallow saucer to slow drying without losing air pruning.
Getting the coir right for either pot
A coir blend with some husk chips stays open enough for air pruning to work and drains well in plastic. Fine pith on its own holds more water, which helps in fabric but risks a wet base in a tall plastic pot. Ratios are in our guide to coco coir for container growing.
CVM Fiber and Industries supplies coco peat blocks, husk chips and custom blends from Kanyakumari, Tamil Nadu, India. The coco peat is washed with water to reduce EC and isn't buffered, with no calcium nitrate or other chemicals added. If you're filling fabric or plastic pots at scale and want help choosing a blend, contact us.
FAQ
Is coco coir better in fabric pots or plastic pots?
Neither is better for everyone. Fabric gives cooler roots and air pruning but dries much faster, so it suits growers who can water often. Plastic holds water longer and suits growers who water less often or need to save water.
How often should I water coco coir in a fabric pot?
More often than in plastic, and in warm weather small fabric pots may need water more than once a day. Lift the pot to judge it and water before the coir dries out completely. Several small irrigations a day work better than one large one.
Do fabric pots really air prune roots?
Yes. Root tips that reach the dry fabric wall stop growing and the root branches further back. In one shrub rose trial, fabric containers cut root circling about fivefold compared with black plastic.
Why is the outside of my fabric pot white and crusty?
Those are fertiliser and water salts left behind as water evaporates through the fabric. The media next to the wall gets much saltier than the centre. Let some water drain at most irrigations and flush with plain water now and then.
Do fabric pots keep roots cooler?
In sun, yes. Evaporation through the wall cools the root zone, and root zones can run many degrees cooler on hot days than in black plastic. In cold weather the same effect makes fabric pots cooler than you might want.
Can I reuse fabric pots with coco coir?
Usually for a few seasons. Knock out the old root ball, soak and scrub off salt crust, and let the fabric dry fully before refilling. Replace pots once the base or seams start to tear.
Should I put a saucer under a fabric pot?
A shallow saucer slows drying and catches runoff indoors. Don't let the pot sit in standing water for long, or the base stays saturated and roots grow into the puddle.