Quick Summary
- Horticultural pumice is a lightweight volcanic rock that dramatically improves drainage, aeration, and root health in potting mixes.
- Unlike perlite, pumice does not float to the surface when you water — it stays mixed throughout the soil profile permanently.
- Different particle sizes suit different plants: fine for succulents and seed raising, medium for general potting, coarse for bonsai and orchids.
- Ausperl and Mineraland are the leading horticultural pumice brands available in Australia.
- Pumice is reusable — you can wash, sterilise, and re-use it indefinitely.
What Is Horticultural Pumice?
Pumice is a naturally occurring volcanic rock formed when lava rich in gases cools rapidly. The result is an incredibly lightweight stone riddled with tiny pores and cavities. These pores are what make pumice so valuable for horticulture: they absorb and hold moisture on their surfaces while the spaces between particles allow excess water to drain freely.
Think of each pumice granule as a tiny sponge wrapped in stone. It holds enough water to keep roots hydrated, but its rigid structure prevents compaction — meaning roots always have access to oxygen, even in a thoroughly watered pot.
Pumice stone for plants has been used by Japanese bonsai growers for decades, but it is rapidly gaining popularity among Australian gardeners for everything from succulents to raised vegetable beds.
Pumice vs Perlite: Why Pumice Wins
Perlite has been the default soil amendment in Australia for years, largely because it was cheaper and easier to find. But pumice outperforms perlite in almost every meaningful way:
| Property | Pumice | Perlite |
|---|---|---|
| Stays in the mix | Yes — dense enough to stay put | Floats to the surface after watering |
| Durability | Lasts indefinitely; does not break down | Crushes into dust over time |
| Water retention | Moderate — holds moisture in pores | Low — sheds water quickly |
| Dust and mess | Minimal | Significant (fine particles irritate lungs) |
| Reusable | Yes — wash and re-use across seasons | Rarely practical to reuse |
| Aesthetic | Natural stone appearance | Bright white — visually distracting |
| Environmental | Mined, but lasts forever | Mined, single-use in practice |
The floating issue alone is reason enough for many growers to switch. If you have ever topped up a pot only to find a crust of white perlite sitting on the surface a week later, you will appreciate pumice's stability.
Particle Sizes and Which Plants Benefit
Pumice for plants comes in several particle size grades. Choosing the right one depends on what you are growing.
Fine Pumice (1–3 mm)
- Best for: Succulents, cacti, lithops, seed-raising mixes, and as a top dressing.
- Why: Fine particles fit neatly around small roots and provide excellent capillary action, keeping the top layer of soil lightly moist without waterlogging.
- Typical mix: 50% fine pumice, 30% quality potting mix, 20% coarse sand for succulents.
Medium Pumice (3–6 mm)
- Best for: General-purpose potting, houseplants, aroids (monstera, philodendron), herbs, and vegetables.
- Why: The most versatile grade. Provides a balanced combination of drainage and moisture retention suitable for the widest range of plants.
- Typical mix: 30% medium pumice blended into standard potting mix transforms drainage and prevents root rot.
Coarse Pumice (6–12 mm)
- Best for: Bonsai soil mixes, orchid media, large container plants, and raised garden beds.
- Why: Maximum drainage and airflow. Coarse pumice is a staple in bonsai substrates alongside akadama, and it is excellent for orchids that need their roots to dry between waterings.
- Typical mix: 25% coarse pumice, 50% akadama, 25% lava rock for a classic bonsai blend.
How to Use Pumice in Your Mixes
As a Soil Amendment (Mix-In)
The simplest approach: add 20–30% pumice by volume to any potting mix. This single change will noticeably improve drainage, reduce the risk of root rot, and encourage stronger root development.
For heavy, water-retentive mixes (like those sold as "premium" potting mix at hardware stores), go higher — up to 40–50% pumice — to counteract the tendency of these mixes to stay soggy.
As a Standalone Substrate
Some growers use pumice as the sole growing medium, particularly for:
- Succulents and cacti in humid climates where overwatering is the primary killer.
- Semi-hydroponic setups where plants sit in pumice with a reservoir of nutrient solution below.
- Propagation — stem cuttings root readily in damp pumice with minimal risk of rot.
As a Top Dressing
A layer of fine pumice on the soil surface serves multiple purposes: it reduces evaporation, discourages fungus gnats (which need moist organic matter to breed), and gives pots a clean, professional appearance.
Pumice in Bonsai
Australian bonsai growers have embraced pumice as an essential component of their soil mixes. Its advantages for bonsai are particularly pronounced:
- Does not break down like akadama, so it provides permanent structural drainage.
- Lightweight compared to lava rock, keeping the overall pot weight manageable.
- Roots grip pumice surfaces readily, anchoring the tree without excessive wiring.
A popular Australian bonsai mix is 50% akadama, 25% pumice, and 25% lava rock — though growers in humid coastal areas often increase the pumice ratio for sharper drainage.
Ausperl and Mineraland: Australian Pumice Brands
Ausperl Pumice
Ausperl is one of Australia's most recognised names in horticultural pumice. Their products are graded for consistency and washed to remove excess dust, making them ready to use straight from the bag. Ausperl pumice is widely used in commercial nurseries and by serious hobbyist growers.
Mineraland Pumice
Mineraland offers premium horticultural pumice in multiple grades, sourced for quality and consistency. Their range is especially popular among bonsai and succulent enthusiasts who need reliable particle sizing.
Both brands are available at Harwood's Garden Supplies.
Tips for Australian Conditions
Australia's climate creates some specific considerations when using pumice:
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Summer heat: In inland areas where temperatures regularly exceed 40°C, a higher proportion of pumice (which holds less water than organic matter) means you will need to water more frequently. Balance drainage needs against practical watering schedules.
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Humid coastal zones: This is where pumice really shines. In Sydney, Brisbane, or the tropics, excess moisture is the primary plant killer. A pumice-heavy mix keeps roots healthy through extended wet periods.
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Frost-prone areas: Pumice's porous structure means it does not crack or degrade in frost, unlike some clay-based amendments. It is perfectly suited to cold-climate gardening in areas like the Blue Mountains, Canberra, or Tasmania.
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Native plants: Many Australian natives evolved in mineral-poor, fast-draining soils. A mix heavy in coarse pumice can replicate these conditions beautifully for species like grevilleas, banksias, and waratahs.
Reusing Pumice
One of pumice's best features is its longevity. When you repot a plant:
- Separate the pumice from old soil using a coarse sieve.
- Rinse thoroughly to remove root debris and old organic matter.
- Optionally sterilise by soaking in boiling water or a dilute hydrogen peroxide solution.
- Allow to dry, then re-use in your next mix.
Pumice lasts essentially forever — buying it once means you have it for life.
Ready to upgrade your potting mixes? Browse our full range of horticultural pumice including Ausperl and Mineraland products, with fast shipping across Australia.