In short: The best all-round coco coir and perlite mix is 70:30 by volume (7 parts coir to 3 parts perlite). Go to 80:20 for seedlings and moisture-loving plants, and 60:40 or even 50:50 for cacti, succulents and fast-draining hydroponic systems. Always measure by volume, not weight, and wet the coir before you mix — dry coir and perlite separate as soon as you water.
Why mix perlite into coco coir at all?
Coco coir is brilliant at holding water — several times its own weight — while still keeping air in the mix. Perlite does the opposite job: the expanded volcanic glass holds almost no water but creates permanent air pockets that never collapse. Together they give you a medium that stays moist without ever going soggy, which matters in the UK where cool, dull weather slows drying. Perlite is also inert and pH-neutral, so it does not change the chemistry of the mix; it simply makes it drain faster and breathe better.
Coir on its own is fine for seed trays and drain-to-waste hydroponics. Add perlite when you are growing in pots for months at a time, when drainage is poor, or when the plant hates wet feet.
The best coco coir to perlite ratio for each job
| What you're growing | Coir : perlite | Why |
|---|---|---|
| Houseplants in pots | 70 : 30 | Even moisture with enough air to stop root rot in centrally heated homes |
| Seed sowing and cuttings | 80 : 20 (fine perlite) | Consistent moisture for germination; fine grade doesn't disturb small roots |
| Tomatoes, chillies and veg in containers | 70 : 30 | Holds water through hot days but drains after heavy watering — see the tomato guide |
| Hydroponic drain-to-waste pots | 70 : 30 or 60 : 40 (coarse perlite) | Faster run-off and more oxygen at the roots with frequent feeding |
| Cacti and succulents | 50 : 50, plus grit | Sharp drainage; the mix dries in days rather than weeks — see coco coir for succulents |
| Raised beds and borders | Use compost as well: 50 : 30 : 20 coir : compost : perlite | Outdoor soil needs nutrition and body, not just drainage — full recipes in the mix ratio guide |
These are starting points, not rules. If a mix stays wet for more than four or five days in a warm room, add perlite; if it dries out within a day or two, add coir.
How to make a coco coir and perlite mix
- Expand the coir. Soak a 5 kg buffered brick in about 20 litres of water for 20–30 minutes until it fluffs up — roughly 75 litres of loose coir. The step-by-step is in how to expand a coco coir brick.
- Measure by volume. Use the same bucket or pot for both ingredients. For 70:30, that is 7 scoops of damp coir to 3 scoops of perlite.
- Dampen the perlite. A quick spray keeps the dust down and stops it floating to the top when you first water.
- Mix thoroughly in a trug or on a tarpaulin until the white flecks are evenly spread — no streaks or pockets.
- Check the drainage. Fill a pot, water it and time the run-off. Water should run through within a minute; if it pools, add more perlite.
A worked example: one expanded 5 kg brick (about 75 litres) plus about 32 litres of perlite gives you roughly 107 litres of 70:30 mix — enough for around twenty 5-litre pots. A 100-litre bag of perlite therefore covers about three bricks at 70:30.
Fine, medium or coarse perlite?
- Fine (1–3 mm): seed trays, plug cells and cuttings.
- Medium (2–6 mm): general pots and containers — the default if you only buy one grade.
- Coarse (6 mm+): hydroponics, cacti, orchids and big containers where you want maximum drainage.
Perlite is dusty when dry. Open the bag outdoors or in a ventilated space, dampen it first and wear a simple dust mask if you are mixing a large batch.
Do you still need feed or compost?
Yes. Neither ingredient contains meaningful nutrients: coir is a near-inert growing medium and perlite is glass. For anything beyond seed sowing, either feed from the first watering with a balanced liquid fertiliser or blend compost into the mix. Our general-purpose container recipe is 50:30:20 — coir : compost : perlite, explained in the coco coir soil mix recipes. Buffered coir matters here too: washed, calcium-buffered coir (pH 5.5–6.5, EC ≤0.5 mS/cm) does not compete with your feed for calcium and magnesium the way raw coir can — the detail is in the buffered vs unbuffered guide.
Coir and perlite: partners, not rivals
People often search "coco coir vs perlite" as if you had to pick one. You don't — perlite is an additive, coir is the base. If you are weighing them up as alternatives, read coco coir vs perlite. If you want more water retention rather than more drainage, vermiculite is the other common partner — compared in coco coir vs vermiculite.
Common mistakes
- Mixing by weight. Perlite is feather-light; 30% by weight would be almost all perlite. Always use volume.
- Mixing dry coir. The perlite sinks and the coir sits on top. Expand and dampen the coir first.
- Too much perlite for the plant. A 50:50 mix dries out fast — great for a cactus, frustrating for a fern.
- Using unbuffered coir. Yellowing leaves a few weeks in are usually calcium or magnesium lock-out, not a perlite problem.
- Reusing without a rinse. Both ingredients can be reused; rinse to flush old salts first — see how to reuse coco coir.
Frequently asked questions
How much perlite do I add to a 5 kg coco coir brick?
About 32 litres for a 70:30 mix, or around 19 litres for 80:20. A 5 kg brick expands to roughly 75 litres, so work from that figure.
Can I use coco coir without perlite?
Yes — on its own it works well for seed sowing, cuttings and drain-to-waste hydroponics, where you water little and often. Add perlite when plants will sit in the same pot for months or when the mix is drying too slowly.
Is 50/50 coco coir and perlite too much?
For most plants, yes: it dries out quickly and needs frequent watering. Keep 50:50 for cacti, succulents, orchids and other plants that want a fast-draining mix.
Does perlite change the pH of coco coir?
No. Perlite is inert and close to neutral, so the mix stays at the coir's natural pH of around 5.5–6.5.
Perlite or vermiculite with coco coir?
Perlite for drainage and air; vermiculite for extra water and nutrient holding. Many seed mixes use a little of both.
Start with the base that behaves: washed, calcium-buffered coco coir bricks, expanding to 75 litres each, delivered free across the UK.
Shop buffered coco coir bricks →