A coco coir grow bag is a compressed slab of coir sealed inside a UV-stabilised plastic sleeve. You lay it flat, push drippers through the film, and the slab swells to fill the bag within a couple of hours. Cut plant holes in the top, slits along the base, and you have a ready-made root zone for tomatoes, cucumbers, peppers or strawberries for one to three seasons.
That's the whole product. The detail is in what's inside the sleeve, how thick the sleeve is, and where the holes go. Those three things separate a bag that drains and dries back the way you planned from one that sits wet all summer.
How a grow bag is made
The slab starts as loose coir pith, or a blend of pith and husk chips, that has been screened and dried. It's pressed into a flat slab, usually 100 cm long, in a hydraulic press, then slid into a polyethylene sleeve and heat-sealed at both ends. Nothing else goes in.
Compression is what makes the format work. A bag that will hold 15 litres of wet coir ships as a flat brick a few centimetres thick. It also means the material arrives bone dry, and dry pith repels water until it has been properly soaked. A sleeve hides the dry spots, which is why the wetting-up routine below matters. The chemistry side is covered in rewetting dry coco coir.
Our coir is washed with water to reduce EC before pressing. We don't buffer it with calcium nitrate, so if your crop needs a buffered bag you charge it yourself during wetting up.
Grow bag, planter bag, open top, slab: the names
Suppliers use these terms loosely, and the same phrase means different things in different countries.
| Term | What it usually means | Where you'll hear it |
|---|---|---|
| Grow bag / growbag | Compressed coir slab inside a sealed sleeve, laid flat, planted through holes in the top | Europe, India, Australia, North America |
| Open-top bag / open top | Coir compressed into a pot-shaped bag with an open upper surface. Planted from the top like a container. Typically 3.5 to 50 litres and 14 to 24 cm tall | Blueberries, raspberries, cannabis, nursery stock |
| Naked slab / grow slab | The compressed slab with no plastic. You put it in your own trough, gutter or pot | Growers with existing trough or gutter systems |
| Planter bag | In Australia and New Zealand, an empty black UV-stabilised poly bag you fill yourself. In India and Sri Lanka, often a coir-filled bag | Nurseries, tree production |
| Plant bag | Catch-all for any plastic bag you grow in, filled or empty | Retail and marketplace listings |
| Ready-to-use (RTU) bag | Loose, pre-hydrated coir in a bag. No expansion step | Indoor and container growers |
When comparing quotes, ask for a photo and the hydrated dimensions rather than relying on the name. The two formats we make are at grow bags and open tops.
Common sizes and volumes
Greenhouse grow bags are almost always 100 cm long so they fit standard gutter spacing. Width and height set the volume.
| Hydrated size (L x W x H cm) | Volume | Typical use |
|---|---|---|
| 100 x 15 x 10 | 15 L | Strawberries on tabletops, 5 to 8 plants |
| 100 x 15 x 12 | 18 L | Retail tomato grow bags, 3 plants |
| 100 x 18 x 15 | 27 L | Tomato, cucumber, pepper, 2 to 3 plants |
| 100 x 20 x 15 | 30 L | Tomato, cucumber, pepper, 3 plants |
| 100 x 20 x 20 | 40 L | High-wire cucumber, long-season tomato |
| Custom up to 120 x 40 x 20 | up to 96 L | Specialist and multi-row systems |
Volume is length times width times height, so check any listing with a calculator. Watch whether the supplier is quoting compressed or hydrated dimensions. Some listings give a compressed size with a hydrated volume, and a few quote volumes the dimensions can't hold.
How much coir does each plant need? In greenhouse tomato trials comparing 5, 7.5 and 10 litres of coir per plant, volume made no difference to yield when plants were irrigated five times a day. At one irrigation a day, the 5-litre plants had more blossom end rot. A smaller bag works if your irrigation keeps up. A bigger bag buys forgiveness when it can't. For most tomato and cucumber crops that means 8 to 10 litres per plant, so a 27 to 30 litre bag with three plants. Strawberries manage on 2 to 3 litres per plant, which is why 15-litre bags carry 5 to 8.
Pith, chip and fibre blends
What's pressed into the slab decides how the bag holds water and air. Pith is the fine, spongy material between the fibres. It holds a lot of water and little air once wet. Chips (also sold as crush) are cut husk, usually screened to 0 to 7 mm or 0 to 15 mm, and they create large pores that drain and let air in. Fibre is the long strand. A little stops a slab slumping. Too much and the bag won't hold together.
The more chip you add, the drier and airier the bag. Here's the range across commercial bags:
| Blend (pith:chip by volume) | Water holding | Air-filled porosity | Where it fits |
|---|---|---|---|
| 100:0 (pure pith) | 60 to 62% | 20 to 25% | Low-frequency irrigation, cool climates |
| 70:30 | 55 to 58% | 30 to 34% | The default for tomatoes, cucumbers and peppers |
| 50:50 | 52 to 54% | 35 to 38% | Hot climates, high-frequency drip, long-season crops |
| 30:70 | 48 to 50% | 40 to 42% | Blueberries, raspberries, crops that hate wet feet |
The percentages are approximate and depend on how fine the pith is and how the chips were screened. Two suppliers' "70/30" can behave quite differently if one uses 0 to 7 mm crush and the other 15 mm chips.
Supplier advice on which blend suits which crop doesn't agree either. Some pair 70:30 with tomatoes and 50:50 with berries. Others say the reverse. The reason is that the right blend depends more on your irrigation than on the crop. A pith-heavy bag under drip that fires every twenty minutes stays saturated. A chip-heavy bag under once-a-day watering dries out by afternoon. Pick the blend for the dry-back you want, then set the irrigation to match. Don't carry an old schedule across to a new blend.
Film specs that matter
Colour. The standard is co-extruded film, white outside and black inside. White reflects sunlight and keeps the root zone cooler. Black stops light reaching the coir, which prevents algae and keeps roots dark. All-black film is sometimes chosen for cool climates or winter plantings where a warmer root zone helps.
Thickness and UV life. Film is sold by gauge or microns, and the UV stabiliser package sets how long it survives under glass before going brittle.
| Gauge | Microns | Typical UV rating |
|---|---|---|
| 300 to 350 | 75 to 90 µm | 1 year |
| 400 | 100 µm | 2 years |
| 500 | 125 µm | 3 years |
Match the film to the number of seasons you plan to use the bag. A one-year film on a bag you intend to run for two strawberry crops will split when you try to move it. The rating assumes greenhouse exposure, so bags stored outside in sun before use lose some of their life before they're planted.
Plant holes, dripper holes and drainage slits
Plant holes sit on the top face. For propagation blocks, a square or round hole in the film sized to the block is enough. For plug plants, the factory can drill into the coir itself, up to about 5 cm across, so the plug sits inside the slab. Spacing follows plant density: three holes for tomatoes on a metre bag, five to eight for strawberries.
Dripper holes are small, around 6 mm, and let you push a stake into the coir without tearing the film. Two per bag is the minimum for even wetting. With three plants, use one dripper per plant.
Drainage slits are where bags get ruined. Cut them low on the side faces rather than underneath, so water can leave but a shallow reserve stays in the base. Cut them on the low side if the bench has a slope. Some factories cut diamond-shaped holes rather than straight slits. Either works, as long as the cut is on the side the water runs to.
Don't cut slits until the bag has fully hydrated and sat saturated for 24 to 48 hours. Water you let out early is water the dry centre of the slab never gets.
Wetting up a new bag
- Lay the bags flat on a level surface with at least 5 cm between them. A bag on a hump drains unevenly for its whole life.
- Fit drippers into the pre-drilled holes. Two per bag minimum.
- Run water in small shots. Fifty to 75 ml per dripper every 5 to 10 minutes is the usual guidance, or shots of about 6% of the final bag volume ten minutes apart. The slab expands over one to two hours.
- Keep going until water pools at the lowest point. A 15-litre bag takes roughly 9 to 10 litres to reach saturation, a 7-litre bag about 4.5 litres. Warm water speeds it up.
- Leave the bag sealed and saturated for 24 to 48 hours. This is when the centre finishes expanding and, if you're charging the coir with calcium, when the exchange happens.
- Cut the drainage slits and let the bag drain. Check EC and pH of the first drain.
- Open the plant holes and plant.
Some suppliers let bags expand over five to seven days under normal drip. That works, but deliberate wetting gives more even expansion. Rushing step 3 is the common mistake. Flooding from a hose pushes water out before the slab absorbs it, and you end up with a soft outside and a dry brick in the middle.
How many crops a bag lasts
Three things wear out at different rates. The film lasts as long as its UV rating, one to three years. The coir itself breaks down slowly and stays physically usable for several seasons. What goes first is the structure: fines migrate to the bottom, roots fill the lower third, and drainage slows. Most commercial growers run a bag for one long crop or two shorter ones. The yield numbers and flushing routine are in reusing coco coir. If you plan to reuse, buy the three-year film and the chip-heavier blend. Both delay the point where the bag stops draining.
Bags or loose blocks?
A bag is a finished root zone. A block is raw material you expand, mix and fill into your own containers or troughs. Bags cost more per litre, save labour, give uniform volumes and drop straight into a gutter system. Blocks cost less and let you set your own blend and volume. The full comparison is on grow bags vs blocks, and growing tomatoes in coco coir walks through a bag-based tomato house.
What to specify when ordering
A manufacturer can make almost any combination. Orders go wrong when a buyer says "100 x 20 x 15, 70/30" and assumes the rest. Put all of this on the spec:
| Item | What to state |
|---|---|
| Hydrated dimensions | Length, width and height in cm, and the volume in litres you expect |
| Blend | Pith:chip ratio by volume, and the chip screen size |
| Washing | Washed to what EC, by which test method. Buffered or not |
| Film colour | White outside / black inside, or all black |
| Film gauge and UV life | 400 gauge / 2 years, 500 gauge / 3 years, or your own figure |
| Plant holes | Number, shape, size and spacing. Film-only or drilled into the coir |
| Dripper holes | Number and position |
| Drainage slits | Pre-cut or left for you. If pre-cut, position |
| Plain, or your branding and lot code | |
| Sample | A few bags to hydrate and test before committing to a container |
The sample matters. Wet up two or three bags, measure the hydrated volume, check the EC of the first drain, and run one for a week under your own irrigation.
If you're specifying bags for a greenhouse project or comparing formats for import, send us the crop, climate and plant density and we'll suggest a size and blend to sample.
FAQ
What is a coco coir grow bag?
It's a compressed slab of coir pith, or a pith and husk chip blend, sealed inside a UV-stabilised polyethylene sleeve. You wet it through dripper holes, the slab swells to fill the bag, and you plant through holes cut in the top. It's the coir equivalent of a rockwool slab.
What size grow bag do I need for tomatoes?
Most greenhouse tomato growers use a 100 cm bag of 27 to 30 litres with three plants, which gives 9 to 10 litres per plant. Trials show smaller volumes work if you irrigate frequently, but they leave less margin on hot days and raise the risk of blossom end rot under once-a-day watering.
How many strawberry plants fit in a grow bag?
The standard strawberry bag is 100 x 15 x 10 cm, about 15 litres, and carries five to eight plants depending on variety and spacing. Many growers choose a chip-heavier blend for strawberries to keep the crowns drier.
What is the difference between a grow bag and an open-top bag?
A grow bag is a flat slab in a sealed sleeve, planted through holes in the top face. An open-top bag is coir compressed into a pot shape with an open upper surface, planted like a container. Open tops are used for blueberries, raspberries and perennials that stay in place for several years.
How much water does it take to hydrate a grow bag?
Roughly 60 to 65 percent of the bag's final volume. A 15-litre bag needs about 9 to 10 litres, a 7-litre bag about 4.5 litres. Add it in small shots over one to two hours rather than all at once, then keep the bag saturated for 24 to 48 hours before cutting drainage slits.
Where should drainage slits be cut?
Low on the side faces rather than underneath, on the low side of the bench if there's a slope, so a shallow reserve stays in the base. Cut them only after the bag has fully expanded and sat saturated for a day or two.
Why are grow bags white on the outside and black on the inside?
White reflects sunlight and keeps the root zone cooler under glass. Black stops light reaching the coir, which prevents algae growth and keeps roots in the dark. All-black film is used where a warmer root zone is wanted, such as winter plantings in cool climates.
How long does a coco grow bag last?
The film is rated for one, two or three years depending on gauge and UV treatment. The coir itself holds up for longer, but drainage slows as fines and roots build up in the base. Most commercial growers run a bag for one long crop or two shorter ones before replacing it.