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How to use perlite in compost: ratios that fit the job

Updated: October 2026

If you have opened a bag and are wondering how to use perlite in compost, start with the job rather than one universal percentage. Improving drainage in a pot, rooting a cutting and preparing a seed mix call for different proportions. Dampen the perlite, measure every component by volume, and remember that perlite does not feed the plant. Our [perlite for plants comparison](/hub/fertiliser-soil-and-bark-mulch/perlite-plants) helps you choose a bag. This page shows what to do once it arrives. The ratios below come from named UK gardening sources, because none of the twelve listings prints a complete mixing recipe.

If you have opened a bag and are wondering how to use perlite in compost, start with the job rather than one universal percentage.

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PLANT !T PLANT!T Perlite 10L

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Swiftair Swiftair Perlite 50L, 2–5 mm

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Swiftair Swiftair Perlite 50L, 2–5 mm
9.5/10about £15.00
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Unbranded Horticultural perlite, 100 litre bag

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Unbranded Horticultural perlite, 100 litre bag
6.6/10about £24.95
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On this page
  1. 1.Dampen perlite before you pour it
  2. 2.Three jobs need different ratios
  3. 3.Perlite will not feed the plant
  4. 4.After mixing: drainage, storage and product problems

Dampen perlite before you pour it

Dry perlite dusts and blows. Dampen it in the bag. Gardeners’ World suggests a couple of litres of water in a whole bag, then seal, shake and wait about 15 minutes. Westland’s example is up to 1 litre in a 10-litre bag. For a partly used bag, add a little, close it and turn it. You want dust suppressed, not free water. One scoop of perlite and four of compost is a 1:4 ratio if you use the same scoop. Wear gloves if the compost label says so, and work where air can move. Do not treat a workplace exposure limit as a home respirator prescription. If a dry bag throws up an unusual cloud, stop and contact the seller.

Three jobs need different ratios

For drainage, Gardeners’ World suggests one part perlite to four parts compost, about one-fifth of the volume. Mix it, use a pot with open holes and water once to settle. Westland’s 25% when potting on is one part perlite in four total parts, not one plus four. Soft cuttings are often equal parts perlite and compost in both Gardeners’ World and Westland. Westland suggests two parts perlite to one part compost for harder cuttings. Do not average those figures. Some cuttings root in damp perlite alone, with no nutrition. Gardeners’ World also gives 50:50 compost and perlite for seeds and cuttings. A covering may be vermiculite instead. See perlite versus vermiculite before you cover a tray, and do not bury very fine seed that needs light. Gardeners’ World’s cactus recipe is three parts low-nutrient compost, two parts sand or grit and one part dampened perlite. Indoor examples are on the perlite for houseplants page.
PLANT !T PLANT!T Perlite 10L

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PLANT !T PLANT!T Perlite 10L
9.1/10about £7.99
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Perlite will not feed the plant

Perlite is inert. The AHDB notes that it does not change growing-medium chemistry and does not lock up nutrients the way some wood fibre can. It is still not a fertiliser. Compost or feed has to supply nutrients. Follow the plant and compost maker after roots establish, rather than feeding extra because the mix looks pale. A high perlite share holds less water, so check the pot instead of watering by the calendar. Perlite is also a poor fit for some hydroponics. Global Horticulture warns that PLANT!T perlite can block drippers or pumps in recirculating systems, and it can float in deep-water culture. Use media the system supplier approves.

After mixing: drainage, storage and product problems

Break up pockets and do not pack the pot hard. Leave headroom so water does not wash granules over the rim. Drainage holes must stay open. Perlite will not empty a sealed cachepot. Store the rest dry, frost-free and away from garden chemicals. Support a bulk sack rather than lifting it by a thin seam. Sizes are compared in the perlite buying guide. A short pack, a wrong variation or heavy contamination is a retailer issue: photograph the label and contents. Settlement can make a bag look smaller. A measured shortfall is different.

Common questions

How much perlite goes into ordinary compost?
Gardeners’ World suggests one part perlite to four parts compost for improved drainage. Measure by volume and regard that as a starting point. A plant that needs consistently moist media may need less, while a specialist cactus recipe uses other mineral ingredients too.
Is a cuttings mix the same as a potting mix?
No. Soft cuttings are commonly placed in equal parts perlite and suitable cutting compost, while ordinary potting mixes often use about 20–25% perlite. Westland suggests two parts perlite to one part compost for harder cuttings, so identify the cutting type first.
Do I wet the bag first?
Yes, lightly dampening perlite before pouring controls dust. Gardeners’ World describes adding water, sealing and shaking a whole bag, then waiting about 15 minutes. Scale the water down for a partly used bag and avoid creating a saturated slurry.
Can I root a cutting in perlite with no compost?
Some cuttings can root in damp perlite alone, but the medium supplies no nutrients and moisture must be managed carefully. An equal-parts mix with seed-and-cutting compost is a more forgiving published method for many soft cuttings.
Will perlite replace plant food?
No. Perlite improves the physical structure of a mix but is inert. Nutrients must come from compost or an appropriate fertiliser. Follow the plant’s feeding requirements after potting rather than assuming white granules contribute fertility.
Why do UK guides give different cutting ratios?
They may be discussing different plants, cutting maturity, composts and propagation systems. Westland distinguishes soft cuttings from harder ones, while other guides provide a general equal-parts recipe. Use one complete method that matches your job instead of averaging unrelated figures.
What if my amazon.co.uk listing gives no ratio?
Use a ratio from a reputable horticultural publisher or the maker of your base compost. None of the twelve listings in this comparison prints a full use ratio. A product description is not a substitute for instructions tailored to your plant.

Related pages

Best perlite for plants

Perlite for plants

Horticultural perlite buying guide: grade and litres

Perlite for houseplants: ratios, floating and bag size

Perlite vs vermiculite: drainage or water-holding flakes

Sources

Public UK and maker sources from the research digest, used for this page in October 2026. Prices, stars and review counts are from the twelve stored amazon.co.uk listings. A shared star line is not a separate sample for each size. Dust warnings are from the cited safety sheets. No exposure was measured at home, and this is not a laboratory test.

  1. RHS, houseplant growing media (retrieved October 2026)
  2. BBC Gardeners' World, what is perlite (retrieved October 2026)
  3. Westland Gro-Sure Perlite (retrieved October 2026)
  4. Vitax Perlite safety sheet (retrieved October 2026)
  5. HSE INDG463, respirable crystalline silica (retrieved October 2026)
  6. AHDB, growing media and liquid feed (retrieved October 2026)
  7. Sinclair perlite grades (retrieved October 2026)
  8. Consumer Rights Act 2015 (retrieved October 2026)