Ausperl horticultural pumice 25L is a natural volcanic growing medium for orchids, cacti, succulents, bonsai and other plants. Mix it with suitable bark, potting mix or mineral ingredients to improve drainage and aeration while retaining some moisture around the roots. Choose from four particle grades to suit your plants, root size and potting method.
Sourced from a land-based deposit within 50 km of Lake Taupō on New Zealand’s North Island, this pumice is washed and screened for horticultural use. The 25L bag suits repotting several plants, preparing your own growing mixes or maintaining a larger plant collection.
Why use pumice for plants?
- Drainage and aeration: spaces between the granules help water drain and air reach the roots. A suitable mix and watering routine help reduce prolonged waterlogging.
- Moisture retention: the porous stone holds some water within and around its pores, providing moisture between waterings.
- Lasting structure: this mineral component does not rot like organic ingredients and helps maintain an open growing medium over time.
- Root support: the textured surfaces and varied particles provide contact points and anchorage for roots.
- Washed and screened: processing reduces unwanted fine material that can clog pore spaces. Some loose dust may still develop during transport.
- Lightweight mineral aggregate: its porous structure makes it lighter than many dense stone aggregates, although a full 25L bag is still heavy.
- Low nutrient buffering: pumice is used mainly to improve the physical structure of a mix. It is not a complete fertiliser, so continue feeding according to the plant and growing system.
Choosing the right pumice grade
| Grade | Suggested uses |
|---|---|
| 1–2 mm | Fine propagation blends and cuttings where good contact around small roots or the cutting base is needed. Ausperl lists conifers, murraya and viburnum as examples. |
| 1–7 mm | A versatile starting grade for cacti, succulents and bonsai mixes, plus smaller orchid plants and selected cuttings. Sieve if you need a narrower particle range for a particular bonsai pot. |
| 4–20 mm | A coarse ingredient for larger pots and open bark blends. It includes smaller particles than the 7–20 mm grade. Select it according to the roots and the other ingredients, rather than treating the two coarse grades as identical. |
| 7–20 mm | A coarse grade for established cymbidiums and other applications needing an open mix. This is the grade used in Ausperl’s published mature-orchid recipe. |
All four options on this page are 25L bags. The millimetre measurement describes the particle grade, not the bag size. Natural material varies, so grades describe a size range rather than identical pieces.
Pumice for orchids
Use pumice as a lasting mineral component in an orchid mix, with bark supplying a complementary structure. Match the grade to the orchid’s roots and pot size. Coarse particles suit established plants with substantial roots; smaller plants need a blend that makes useful contact around their roots.
Established cymbidiums
Ausperl’s example uses 40% 7–20 mm pumice, 30% coarse bark and 30% medium bark. To prepare a nominal 10L batch, measure 4L pumice, 3L coarse bark and 3L medium bark before mixing.
Smaller cymbidiums and young plants
For a cymbidium seedling or cycad pup mix, Ausperl lists 40% 1–7 mm pumice, 30% medium bark and 30% fine bark. A nominal 10L batch uses 4L pumice and 3L of each bark grade.
These are cymbidium examples, not one recipe for every orchid. For other orchids, match the medium to the species, root thickness, airflow and watering conditions. Check how quickly the new mix dries instead of carrying over your previous watering schedule unchanged. Browse our orchid potting mixes for complementary ingredients.
Pumice for cacti and succulents
Cacti and succulents that need an open growing medium can benefit from pumice mixed throughout the root zone. The 1–7 mm grade is a practical starting option. Choose the final proportions for your species, the organic ingredients already in the mix and how quickly the pot dries in your conditions.
- Adding to an organic potting base: the general blend previously provided for this product is 30% pumice with 70% suitable organic substrate. For a nominal 10L batch, measure 3L pumice and 7L of the base. Treat this as a starting blend, not a guarantee that every existing potting mix will drain adequately.
- Ausperl’s echeveria example: 60% 1–7 mm pumice, 20% coarse sand and 20% peat moss. Measure 6L pumice, 2L coarse sand and 2L peat moss for a nominal 10L batch.
The two blends have different water-holding properties. Trial a small batch before repotting a whole collection. Use clean horticultural coarse sand where specified. Choose a purpose-made potting base for containers; heavy garden soil can restrict drainage and aeration. A cactus or succulent mix that already contains substantial mineral ingredients may need little or no additional pumice.
In cool, shaded or wet conditions, pay particular attention to how long the root zone stays moist. In hot, exposed conditions, a very open mix can need more frequent checking. Browse our cactus and succulent potting mixes to choose a suitable base.
Pumice for bonsai
Pumice can form part of a mineral bonsai mix with akadama and lava rock. Aim for a particle size that suits the tree, roots and container. For many bonsai applications, start by assessing the 1–7 mm grade and sieve it if a more uniform size is required. The coarse 7–20 mm grade will be too large for many small bonsai pots.
Bonsai Empire gives these general examples, which should be adjusted for the tree species and growing conditions:
- Deciduous bonsai: 50% akadama, 25% pumice and 25% lava rock — a 2:1:1 ratio.
- Conifers and pines: equal parts akadama, pumice and lava rock — a 1:1:1 ratio.
Use ingredients with compatible particle sizes so a very fine component does not fill all the spaces between coarser particles. Check moisture frequently after changing the mix, especially in shallow pots. Continue an appropriate bonsai feeding programme. See our bonsai potting mixes and growing media for complementary ingredients.
Other pumice uses
Propagation and cuttings
The smaller grades provide contact around the cutting base while maintaining air spaces. Ausperl publishes the following examples:
| Cutting type | Grade | Starting recipe | Plant examples |
|---|---|---|---|
| Hardwood / slow rooting | 1–2 mm | 100% pumice | Conifers |
| Softwood | 1–2 mm | 50% pumice + 50% peat moss | Murraya, viburnum |
| Hardwood / slow rooting | 1–7 mm | 100% pumice | Maples, camellias |
| Stem cuttings | 1–7 mm | 40% pumice + 30% coarse sand + 30% peat moss | Frangipani, cordyline |
Use clean propagation equipment and follow the cutting technique for the species. Pure pumice is a rooting medium for selected applications, not a universal recipe for raising every plant. Keep moisture appropriate to the cutting and transition to a suitable growing and feeding programme once rooted. The cymbidium seedling recipe above is a specific orchid mix, not a fine seed-sowing formula for all seeds.
Indoor plants, herbs and other container plants
Where a plant needs a more open root environment, incorporate an appropriate pumice grade into a suitable potting base. This can be useful for adjusting mixes for foliage plants or potted herbs, but the amount depends on the starting mix and the plant. Assess a small trial pot rather than adding the same percentage to every product. Already coarse mixes and plants needing consistent moisture may require less adjustment.
Hydroponics and mineral growing systems
Pumice can support roots in a suitable aggregate hydroponic system. Match the grade to the container, irrigation method and drainage openings. Supply a complete hydroponic nutrient solution and monitor nutrient strength and pH for the crop. Pumice alone does not provide complete plant nutrition, and a passive reservoir needs its own moisture and irrigation assessment.
Green roofs and lasting landscape mixes
Pumice is used in designed green-roof substrates where drainage, moisture storage and lasting structure matter. Follow the project’s growing-medium specification, including saturated weight, drainage and plant requirements. A 25L horticultural bag is an ingredient, not a complete engineered roof system.
Surface dressing and garden beds
A suitable grade may be used as a surface dressing for a mineral finish. This does not replace a well-drained root-zone mix. For garden beds, assess the soil and the reason for poor drainage first; a small quantity of pumice around a planting hole will not correct a broader drainage problem.
How to mix and use pumice
- Choose the grade and recipe. Match them to the plant, roots, pot size and growing conditions.
- Measure ingredients by volume. Use the same scoop or bucket for each part. For example, 40% means four parts pumice in ten parts of measured ingredients. Mixed volume can settle, so batch totals are approximate.
- Prepare the material. Handle gently to limit dust. Lightly dampen dusty material and rinse off loose fines if needed. Washing and screening should not be taken as a guarantee of sterility.
- Blend evenly. Mix through the root-zone medium. A separate coarse layer at the bottom of a pot does not improve drainage through the finer mix above it.
- Use suitable containers. Keep drainage holes clear and let excess water escape. Avoid leaving an ordinary potted plant standing in collected water.
- Adjust after repotting. Follow the plant’s repotting guidance, check moisture and adapt watering and feeding to the new mix.
Planning quantities: at 25% pumice, a 25L bag supplies the pumice portion of approximately 100L of measured ingredients; at 40%, approximately 62.5L; at 60%, approximately 41.7L. These are mixing calculations, not guaranteed final packed volumes or a fixed number of pots.
Need a smaller amount? Choose our 5L horticultural pumice, or compare pumice products, grades and bag sizes.
What is pumice?
Pumice is a porous volcanic rock formed when gas-rich lava cools and depressurises rapidly, leaving a network of bubbles within the solid material. Its internal pores hold some moisture, while the spaces between particles help provide air and drainage in a growing medium. This combination explains its use in both horticultural mixes and selected hydroponic applications.
Frequently Asked Questions
Q. Which pumice grade is best for growing Succulents?
A. According to the manufacturer, they suggest using mostly 1- 4 mm with a little 4- 10 mm mixed in. The pumice should also be mixed with 50 to 75% of fine to medium organic matter like compost and garden soil.
Q. What is the PH of this pumice?
A. According to the manufacturer, "The pH of Pumice is typically pH 6.7 to 6.9"
Q. What is the country of origin for this pumice?
A. It's from New Zealand.
Q. How much does a 25L bag weigh?
A. The weight of this item can vary significantly due to the moisture content or the weight of the pumice rock. We tested some bags at around 21 kg, but this can vary.
Current grade and mixing clarification: the succulent FAQ above refers to the manufacturer’s 1–4 mm and 4–10 mm grades. Those are not selectable options on this listing. This product offers 1–2 mm, 1–7 mm, 4–20 mm and 7–20 mm. Ausperl also publishes the 1–7 mm echeveria recipe shown above. These are different starting blends; select one appropriate to your plants and conditions. For containers, a suitable potting substrate is generally preferable to heavy garden soil.
Handling and storage: avoid breathing dust and follow the packaging instructions. Keep stored material covered and away from contamination. Bag weight varies, so use suitable lifting assistance for a full bag.
Always read and follow the instructions on the product packaging and/or seek expert advice before use, and don’t depend on information on this page that may have errors or be outdated.