The short answer: for a general houseplant mix, start at 60 to 70% coco coir pith with 30 to 40% perlite or husk chips by volume, add a slow-release feed that contains calcium and magnesium, and you have a peat-free mix that re-wets after drying, holds air when wet and suits pothos, philodendron, peace lily and most foliage plants. Aroids such as monstera want coir cut back to 20 to 35% of a chunky bark and chip mix. Succulents and cacti want coir down to roughly a fifth of the volume in a mineral mix. The recipes below are by volume, and the rest of the article covers why coir behaves the way it does indoors, how watering and feeding change compared with peat, and what to write into a specification if you're bagging mixes for retail.
Why coir suits indoor plants
Three things make coir a good base for houseplant mixes, and one thing needs managing.
It re-wets. A houseplant gets forgotten. Peat that dries past a point turns water-repellent and the water runs down the pot wall and out the drainage hole while the root ball stays dry. Coir dried to 33% moisture by weight still takes water up and gets back to full capacity over a few waterings, while peat at the same moisture is fully hydrophobic.
It keeps air when wet. A 70/30 coir and perlite mix in a 6-inch pot measured at 22% air space and 59% total water-holding capacity after saturation. The peat equivalent came out at 24% air and 52% water. So coir holds more water at a similar air content, which suits a plant watered once a week and then left.
Its pH sits where houseplants want it. Coir pith comes in around 5.5 to 6.5, so it needs no lime, unlike raw peat at about 4.4.
The part that needs managing is nutrition. Coir arrives loaded with potassium and almost no calcium or nitrogen, and it can tie up nitrogen while it breaks down. More on that below, because it changes what fertiliser goes in the bag.
On the demand side, garden-centre customers in the UK and much of Europe now ask for peat-free houseplant compost by name, and coir is what most of those bags are built on. If "compost" versus "potting mix" wording confuses your customers, coir compost explained covers it.
Recipes by plant group
All ratios are parts by volume. "Pith" means fine or medium coco peat, "chips" means coconut husk chips of 6 to 12 mm unless stated.
General houseplant mix
| Ingredient | Standard | Thirsty plants (peace lily, ferns in bright rooms) | Drier rooms, less frequent watering |
|---|---|---|---|
| Coir pith | 6 | 7 | 7 |
| Perlite | 3 | 2 | 2 |
| Husk chips (6 to 12 mm) | 1 | 0 | 1 |
| Vermiculite | 0 | 1 | 0 |
The standard column is the 60/30/10 mix for pothos, philodendron, dieffenbachia, peace lily, dracaena (see the fluoride note below), ficus and most foliage plants in plastic or glazed pots. The chips add drainage channels perlite alone doesn't, and slow the mix's collapse over two or three years. For terracotta, which dries faster, use the right-hand column.
Aroids and chunky mixes
Monstera, philodendron, anthurium, alocasia and syngonium have roots built to run over bark and through leaf litter, not sit in wet pith. Published chunky-mix recipes vary, but coir lands between 20 and 35% of the volume in nearly all of them, with bark the largest ingredient.
| Ingredient | Monstera and climbing philodendron | Anthurium and velvet-leaf aroids | Alocasia and thirstier aroids |
|---|---|---|---|
| Orchid or pine bark (6 to 12 mm) | 4 | 4 | 3 |
| Coir pith | 1 | 0 | 2 |
| Husk chips (6 to 12 mm) | 1 | 1 | 1 |
| Perlite or pumice | 3 | 3 | 2 |
| Worm castings or compost | 0.5 to 1 | 0.5 | 1 |
| Horticultural charcoal | 0.5 | 0.5 | 0.5 |
Pith is the moisture buffer in these mixes and husk chips are the structure. Anthurium wants almost no pith, so it takes chips only. A retail "aroid mix" that is mostly pith with a handful of bark will grow pothos fine and rot a monstera in a cool room, so if you're bagging one, keep pith under a third. Chip grades, and how chips compare with bark, are in coco coir for orchids and anthurium.
To adjust: a pot that stays wet for several days needs more bark or perlite, and a plant in a very dry home or strong light can take another half part of pith.
Succulents and cacti
Coir holds too much water to be the base of a cactus mix, but a small share of it stops the mineral fraction from drying out completely and becoming hard to re-wet.
| Ingredient | Parts |
|---|---|
| Coarse grit, pumice or coarse sand | 4 |
| Perlite | 2 |
| Coir pith | 1 to 2 |
| Husk chips (6 to 12 mm) | 1 |
That puts organic material at roughly a fifth to a third of the volume, in line with the rule for drought-tolerant plants of keeping the soilless fraction to no more than a third. Use coarse builder's sand if you use sand at all, never fine play sand. A mix needs to approach half sand before sand alone drains quickly, which is why grit and pumice do the job better.
Ferns and calatheas
Ferns and calatheas want an even moisture that never dries fully but also never sits in water. The traditional fern recipe is equal parts houseplant potting mix and peat or leaf mould. Coir replaces the peat half directly.
| Ingredient | Parts |
|---|---|
| Coir pith | 5 |
| Fine bark or leaf mould | 2 |
| Perlite | 2 |
| Worm castings or compost | 1 |
Feed ferns lightly, about half the labelled rate once a month through the growing season, and not at all in winter or for six months after repotting. Calatheas and marantas are salt-sensitive and, as monocots, among the plants more prone to fluoride injury, so the water quality section below applies to them as much as to dracaena.
Watering: how a coir mix behaves compared with peat
Coir mixes hold more water than peat mixes at the same air content, and the surface goes pale and dry while the middle of the pot is still wet. Customers who water on how the top looks will overwater. Tell them to push a finger in to the first joint, or 5 to 8 cm in a larger pot, and water only if it's dry at the fingertip. Or lift the pot. The weight difference between wet and dry is obvious after a week.
Water until it runs from the base, then empty the saucer. Wetting a container from dry takes roughly 45 to 60% of the pot's volume in water, so a 10-litre pot wants 4.5 to 6 litres, not a cupful. Running water through to the drain also carries excess salts out, which matters more in coir than in peat because coir has little buffering and takes up whatever the tap water brings. Avoid softened water, which adds sodium.
If a coir mix has dried hard in a neglected pot, water it, wait half an hour and water again, or stand the pot in a bucket until the surface darkens. Coir recovers from this. Peat often doesn't.
Feeding: potassium high, nitrogen and calcium low
Coir is neither inert nor complete. Measured coir sources have tested at roughly 4,400 to 20,000 ppm potassium against 99 ppm in peat, and 9 to 16 ppm calcium against 127 ppm in peat. High potassium also gets in the way of magnesium uptake. So a coir mix fed with a tomato-type feed, which is high in potassium and has no calcium, goes wrong over a long-lived houseplant.
Nitrogen is the other gap. Coir has a high carbon-to-nitrogen ratio, and media with more than 50% coir have shown reduced growth that the researchers put down to nitrogen being tied up by microbes. Supplying extra nitrogen weekly at 10 mg per litre of substrate closed the gap in trials.
What this means for a retail bag or a home mix:
- Use a complete fertiliser that includes calcium and magnesium, not plain N-P-K. A gypsum addition is the standard way to bring calcium into a coir mix without moving the pH.
- Include a controlled-release feed in the bag so the plant isn't relying on the customer. Controlled-release products avoid the initial salt spike that granular feeds cause and carry a plant for months. A pre-plant charge usually needs a top-up after 8 to 10 weeks.
- Lean the nitrogen slightly higher than you would for a peat mix in the first months.
- Add Epsom salt (magnesium sulphate) if older leaves yellow between the veins, which is the magnesium symptom that high potassium brings on.
Whether to buy washed-only or fully buffered coir for the base is a separate decision. Buffered coir has had the potassium and sodium on its exchange sites swapped for calcium, which removes most of the feeding caveats above at a higher raw-material price. Buffered vs unbuffered coco peat covers the trade-off. Our coco peat is washed with water to reduce EC, with no calcium nitrate or other chemicals, and is not buffered, so pair it with a calcium-containing feed.
Salt- and fluoride-sensitive plants
Dracaena, spider plant, lilies and Tahitian bridal veil are the classic fluoride-sensitive houseplants, and monocots in general are more susceptible. Fluoride shows up as scorched leaf tips and margins. The usual sources are fluoridated tap water, single superphosphate fertiliser and, to a lesser extent, perlite.
For these plants:
- Keep the mix pH between 6.0 and 6.5. Fluoride becomes less available as pH rises, and coir sits in that range naturally.
- Avoid high-perlite mixes. Swap the perlite in the general recipe for husk chips or pumice.
- Don't use fertilisers containing superphosphate.
- Water with rainwater or filtered water where tap water is fluoridated.
For salt sensitivity in general, washed coir with a low EC is the starting point, and the first few waterings after potting should run through to the drain. Calatheas, marantas, ferns and peace lilies show brown tips from salt as readily as from fluoride.
Keeping fungus gnats out of retail mixes
Fungus gnat larvae live in the top 5 to 8 cm of the medium and feed on fungi, algae and decaying organic matter. Egg to adult takes three to four weeks at room temperature, and indoors they breed all year. A constantly wet surface and fresh organic matter such as unfinished compost both encourage them.
- Let the top 2.5 to 5 cm dry between waterings. That alone cuts egg and larval survival sharply.
- Keep compost or worm castings to 10% or less in retail mixes, and use finished, screened material.
- A top layer of husk chips or grit dries fast and gives females nowhere to lay.
- For an infested pot, yellow sticky cards catch adults, a potato slice pressed into the surface shows whether larvae are present, and a drench of the nematode Steinernema feltiae kills larvae within three to four days.
Coir itself is not more gnat-prone than peat. Wet coir topped with compost is. More on telling gnats from harmless surface mould is in mould, algae and fungus gnats in coco coir.
What to specify when sourcing coir for retail bagging
If you're producing mixes rather than buying them, the coir specification does most of the quality work. Write down:
| Item | What to ask for | Why |
|---|---|---|
| Grade | Fine or medium pith for the base, 6 to 12 mm chips separately, or a stated pith-to-chip blend | Chips bought separately let you run several recipes from two raw materials |
| Washing and EC | Washed with water, EC stated with the extraction method (1:1.5 by volume is the common one) | Washed coir keeps potassium on its exchange sites, so EC alone won't show K; the method matters because figures aren't comparable across methods |
| Buffering | State washed-only or buffered, and if buffered, what with | Changes the feed you put in the bag |
| Moisture at pressing | Below 15 to 20% by weight | Blocks pressed wetter mould in storage and expand unevenly |
| Compression | State the ratio (pressing trials run 4:1 to 6:1), and the moisture it was pressed at | Harder pressing saves freight but breaks down structure toward finer, wetter material |
| Expanded yield | Litres per kilogram and how it was measured | A 5 kg block gives roughly 60 to 75 litres, and a 650 g briquette 8 to 10 litres, and anything quoted well above that deserves a question |
| Sand and foreign matter | Sieve test on the hydrated sample | Sand adds weight and nothing else |
For a small producer, 650 g briquettes are the practical format: one briquette hydrates to roughly a 9-litre bag's worth of pith. At pallet scale, 5 kg blocks and loose chips are cheaper per litre, and hydration is covered in the coco peat blocks guide. If the recipe is fixed, a pre-blended pith-and-chip block removes the mixing step.
FAQ
Can I grow houseplants in 100% coco coir?
You can, but most plants do better with 30 to 40% perlite or husk chips added. Pure pith holds a great deal of water and compacts over time, so roots in the bottom third of the pot sit wetter than you'd like. Pure coir also needs a complete feed from day one, because it carries almost no nitrogen or calcium.
What ratio of coco coir should an aroid mix have?
Between 20 and 35% of the volume, with bark as the largest ingredient and perlite or pumice making up a quarter to a third. Monstera and anthurium sit at the low end, alocasia and the thirstier philodendrons at the high end. Husk chips can replace some or all of the pith for a chunkier result.
Do coco coir mixes need lime like peat mixes?
No. Coir pith comes in around pH 5.5 to 6.5, which already suits most houseplants, and adding the lime rate you'd use for peat pushes it too high. Add calcium as gypsum instead, which supplies calcium without raising the pH.
Why are the leaf tips on my dracaena or spider plant turning brown in coir?
Both plants are sensitive to fluoride, and the usual sources are fluoridated tap water, superphosphate fertiliser and, to a lesser extent, perlite. Switch to rainwater or filtered water, use a mix with chips or pumice instead of perlite, and keep the pH between 6.0 and 6.5. Salt build-up causes the same symptom, so flush the pot through to the drain as well.
How often should I water houseplants in a coir mix?
Less often than the surface suggests. Coir dries pale on top while the root zone is still wet, so check with a finger to the first joint or by lifting the pot. Water thoroughly until it drains, empty the saucer, and don't water again until the mix is dry at finger depth.
Does coco coir cause fungus gnats?
Not on its own. Gnats need a wet surface and decaying organic matter, so a coir mix with a lot of compost that is watered every few days is a gnat farm, and a coir mix with a dry top layer of chips is not. Let the top 2.5 to 5 cm dry between waterings and keep compost to a small share of the mix.
What fertiliser suits coco coir houseplant mixes?
A complete feed that includes calcium and magnesium alongside nitrogen, phosphorus and potassium. Coir already carries plenty of potassium and very little calcium, so a high-potassium tomato feed is the wrong choice. A controlled-release product mixed into the bag covers the first few months.
Is a coir houseplant mix really peat-free?
A mix built on coir pith, husk chips, bark and perlite contains no peat. Check the other ingredients though. Some "coir-based" retail mixes still include a peat fraction for texture, and only the ingredient list on the bag tells you.
If you're planning a retail houseplant range and want to talk through grades, pith-to-chip blends or compressed formats, get in touch.