Perlite vs Vermiculite, Expanded Clay and Pumice

In short: Perlite makes soil airy and is very light. Vermiculite stores far more water and nutrients. Expanded clay (LECA, called “Blähton” in German) is coarse, keeps its shape and is ideal for hydroponics and drainage. Pumice and lava rock are heavier, very stable in structure and popular for cacti and roof gardens. Which material is right depends on whether your plant needs more air or more water.

Five materials, one job

All five materials share the same basic job: they give potting soil structure so that it does not compact and the roots get enough air. They are mineral, do not rot and – unlike compost or soil – bring practically no nutrients with them. The differences lie in how they are made, their weight and, above all, how much water and how many nutrients they hold on to.

• Perlite is volcanic glass that is expanded to about ten times its volume at around 850–1200 °C.
• Vermiculite is a mica-like layered mineral. When heated above 850 °C, the water in its crystal structure escapes and the flakes expand like a concertina to 10 to 35 times their size.
• Expanded clay (LECA) is formed from clay and fired at 850–1200 °C. The result is round pellets with a porous core and a largely closed outer skin.
• Pumice is a naturally porous volcanic rock formed in volcanic eruptions and only crushed and sieved.
• Lava rock (lava granules, scoria) is also volcanic in origin, reddish-brown to grey-black and somewhat less porous than pumice.

The comparison table

The table summarises typical properties. Individual products may differ – especially in pH, which for pumice, lava rock and expanded clay depends strongly on origin and manufacture.

Perlite or vermiculite?

This is the most common question – and the answer depends on the goal.

Perlite is the air specialist. Its hard, rugged grains create large pores through which water drains. It stores hardly any nutrients and does not change the pH.

Vermiculite is the specialist for water and nutrients. The fine flakes soak up water like a sponge and can bind and release potassium, ammonium and magnesium. According to LSU AgCenter, its cation exchange capacity is about a hundred times that of perlite. The downside: the flakes are not very stable and get squashed together over time.

Measurements from the University of California show how differently the two behave: a 1:1 mix of peat and perlite contained 20% air and 73% water, while a 1:1 mix of peat and vermiculite contained only 13% air but 81% water.

Rule of thumb:

• The plant likes it airy and cannot tolerate waterlogging (cacti, succulents, aroids, orchids in mixes): perlite.
• Seeds or young plants that should stay evenly moist: vermiculite or a mix of both.
• Cuttings: usually perlite, because the cut ends are more likely to rot in a very wet growing medium.

Perlite or expanded clay?

Expanded clay – known as hydroponic clay pellets or LECA – is coarse and keeps its shape very well. The firing process takes away the clay’s ability to bind water in its structure and to exchange nutrients. Expanded clay is therefore excellent for hydroponics, as a drainage layer at the bottom of pots and for green roofs, but less suitable as an additive in fine potting compost. Another point: according to COMPO, expanded clay is energy-intensive to produce – although that applies to all fired or expanded materials, including perlite and vermiculite.

In fine potting compost, perlite distributes more evenly. For pure hydroponic systems with large pots and for drainage, expanded clay is usually the more practical choice. White deposits on expanded clay are salt residues, not mould.

Perlite or pumice and lava rock?

Pumice and lava rock are naturally porous and do not need to be expanded. They are much heavier than perlite, do not float up and stay completely stable in structure for many years. That is why they are popular in cactus and bonsai mixes, in roof-garden substrates and in tree substrates. According to IVG, pumice has a “fairly high” pH and a low cation exchange capacity; lava rock holds somewhat less water than pumice.

For cacti and succulents, a combination is often ideal: perlite for lightness, pumice or lava rock for weight and stability. For houseplants in ordinary potting compost, perlite is usually the simpler choice because it is light and mixes in easily.

And what about sand and gravel?

Sand and gravel are the cheapest mineral additives. They improve drainage in garden soils and cactus compost but make the growing medium heavy. For pots, balcony boxes and roof gardens, light materials such as perlite have the advantage.

Choosing the right one at a glance

Our conclusion

There is no single best material. Perlite is the most versatile all-rounder for potting compost, seed starting and cuttings – light, neutral and airy. Vermiculite fills in where moisture matters more than air. Expanded clay, pumice and lava rock play to their strengths in coarse, particularly structure-stable substrates.

We at ACAR Gartenbedarf have specialised in perlite. If you would like to know whether perlite is the right choice for your project, just ask us – we will tell you honestly if another material suits better. To our product: perlite · Enquire directly: contact