Perlite makes potting soil loose, airy and evenly moist. From Basel we advise you personally on the grain size and quantity that suit your project – from the balcony to seed starting and hydroponics.
Perlite (in German also spelled “Perlit”) is a volcanic rock: a glassy, rhyolitic lava rock formed when lava cools quickly, containing 3–5% bound water. When the crushed raw rock is heated suddenly to 850–1200 °C, this water turns to steam and puffs up each grain – much like popcorn. The result is a white, porous and extremely light granulate with a pore volume of around 97%.
In plant growing, perlite is a real all-rounder: as an additive that keeps soil loose for good, or as a pure medium for cuttings and hydroponics. Because perlite is chemically almost inert, it changes neither the pH nor the nutrient supply of your soil – it only improves the structure.
More in the guide: What is perlite?
Which grain size you need depends on the use: fine grades hold more water, coarse grades provide more air.
| Grain size | Typical use |
|---|---|
| fine, approx. 0–3 mm | sowing, seed-starting compost, fine mixes, lawns and sandy soils |
| medium, approx. 2–6 mm | all-round: houseplants and balcony plants, cuttings, raised beds, planters |
| coarse, approx. 4–8 mm | coarse mixes with bark (e.g. aroids, orchids), cacti, drainage |
The hard, porous grains stop soil from compacting. Air stays in the root zone, excess water drains better and the risk of waterlogging and root rot falls.
Perlite holds water on its rugged surface and in the gaps between grains, releases it to the roots and lets air through at the same time. That gives more even moisture.
Perlite is sterile from the factory thanks to the heat. It is pH-neutral and brings no nutrients – you keep full control over feeding and pH. Ideal for propagation.
Perlite is very light: 100 litres weigh only about 10–13 kg when dry. Pots, balcony boxes and roof gardens become noticeably lighter. And because perlite does not rot, the structure of your soil lasts for years.
Whether repotting on the balcony, propagating on the windowsill or growing hydroponically in the greenhouse: perlite is versatile and easy to handle.
Guide values in percent by volume of perlite in the finished mix. Details and tables in the guide How to mix perlite.
10–30%
Mix 10–30% perlite into good-quality potting soil, as a rule of thumb about 20% (1 part perlite to 4 parts soil). For plants that like it airy – such as monstera, philodendron or hoya – go towards the upper end.
20–30%
Seed-starting compost with 20–30% fine perlite, up to 30% for seed trays. For sowings, 1:1 mixes with seed-starting compost are also common. The loose medium makes it easier for fine roots to grow through.
approx. 20%
In a raised bed or planters, mix about 20% perlite into the top layer. For Mediterranean herbs that like dry feet, use a little more.
pure or 20–30%
Perlite can be used pure as a medium, or mixed at 20–30% into another medium (e.g. coco) in ebb-and-flow systems.
pure or 1:1
Cuttings root in pure perlite or in a 1:1 mix of perlite and seed-starting compost (or coco). More in the guide Cuttings, propagation and hydroponics.
30–50%
30–50% mineral content so the mix dries out quickly. Perlite combines well with pumice, lava rock or gravel.
5–10 L/m²
Heavy, clayey garden soils: work in about 10 litres per m². When renovating a lawn, rake in 5–10 litres per m² after scarifying.
Typical values for expanded horticultural perlite from manufacturer data and technical literature. They are not guaranteed specifications of our product.
| Property | Typical value |
|---|---|
| Material | expanded volcanic glass (rhyolite), amorphous |
| Main components (raw rock, before expansion) | approx. 70–76% silicon dioxide (SiO₂), 11–18% aluminium oxide (Al₂O₃), 4–6% potassium oxide |
| Expansion temperature | approx. 850–1200 °C |
| Volume increase on expansion | about 10-fold, up to 20-fold depending on the raw material |
| Bulk density (horticultural grade) | approx. 96–128 kg/m³ (100 L ≈ 10–13 kg) |
| Total pore volume | approx. 97% by volume |
| Water-holding capacity | approx. 19% (very coarse) to 52% (fine) of volume |
| pH | neutral, approx. 6.5–8.0 |
| Nutrients | practically none (N, P₂O₅, K₂O each < 4 mg/l) |
| Cation exchange capacity | very low (approx. 1.5 meq/100 g) |
| Salt content | very low (EC approx. 4 mS/m) |
| Hygiene | sterile from the factory thanks to the heat treatment |
| Durability | does not rot, keeps its shape, stays effective for years |
| Classification (CLP) | not classified as a hazardous substance |
Typical values for expanded perlite taken from manufacturer data and technical literature; not guaranteed product specifications.
Perlite is not classified as a hazardous substance. Like any fine mineral material, however, its dust can irritate the eyes and airways. This keeps handling low in dust:
Dry or wet, warm or cold – perlite does not spoil. Close opened bags so that no dirt, seeds or pests get in: perlite is only sterile from the factory.
Used perlite can be reused: remove root remnants, rinse thoroughly in a sieve and let it dry; after diseased or infested plants, pour boiling water over it. Small amounts can simply be worked into garden soil or compost. Dispose of larger amounts according to your municipality’s rules.
For most houseplants and balcony plants 10–30% perlite is enough, as a rule of thumb 1 part perlite to 4 parts soil (20%). Cacti and succulents tolerate 30–50% mineral content, and cuttings will even root in pure perlite.
For sowing and fine seed-starting compost, fine perlite (approx. 0–3 mm) is suitable; for most uses, medium (approx. 2–6 mm); and for coarse, airy mixes, coarse (approx. 4–8 mm). If in doubt, medium is the most versatile choice.
According to safety data sheets, perlite is not classified as a hazardous substance. The fine dust can irritate the eyes and airways – so moisten perlite before use and wear a dust mask for larger quantities. Perlite is not intended to be eaten.
No. Perlite is practically nutrient-free and chemically almost inert. It only improves the structure of the soil; feed as usual.
No. Perlite is pH-neutral (typically 6.5–8.0) and hardly buffers at all. The pH of your mix is determined by the soil.
Perlite mainly provides air and drainage, while vermiculite stores considerably more water and nutrients. For airy soil and against waterlogging perlite is the better choice; for evenly moist sowings vermiculite can make sense. More in the comparison of perlite, vermiculite and clay pebbles.
Yes. Perlite does not rot: remove root remnants, rinse thoroughly and let it dry. After diseased plants, pour boiling water over it first.
Perlite is very light and can float up when the grains are dry or when watering heavily. Remedy: dampen perlite before mixing, mix it well into the soil and cover the top layer with soil.
Not always. Perlite for plants is untreated. Some construction perlite for insulation fill is bitumen-coated or treated to repel water and is not meant for plants. Look for the label “horticulture” or “for plants”.
Tell us what you need perlite for and how much – you will receive a no-obligation quote.