Pumice 3/8 mm - 5 litre pack

What it is and where it comes from

Pumice is a light, highly porous volcanic rock, formed when lava solidifies while trapping gas. Here it comes sieved to a 3/8 mm grain and packed in 5 litres. It is an inert material: it supplies no nutrients, it works on the structure of the substrate.

How it behaves in the pot

Water passes through and does not stagnate. The pores of each grain hold a reserve of moisture that the plant draws on between waterings, while the rest drains away and leaves room for air. It is precisely this alternation between pockets full of water and pockets full of air that pushes the root system to branch into fine roots.

In terms of durability, pumice is among the most reliable materials available. The grain does not turn to paste, does not break down with frost and reaches the next repotting with the same shape it had the day it went into the pot: no compaction, no suffocating clay around the roots.

Specifications

• Material: pumice, natural inert material of volcanic origin
• Grain size: 3/8 mm
• Pack: 5 litres
• Use: drainage component for bonsai substrates

Which grain for which plants

3/8 pumice is a medium-coarse grain. It works well in the body of the substrate for medium and large bonsai, while in the shallow pots used for shohin it is bulky and is better kept for the bottom layer only. As a drainage layer beneath the roots it is perfect: it never closes up and keeps the drainage holes clear.

It pairs well with any component that holds more moisture, from akadama to organic soil, and on conifers many growers use it generously because they tolerate wet feet poorly. It can also be used on its own, a common choice in the early establishment phase of nursery plants or freshly collected material, when air matters more than nutrition.

How to use it when repotting

Sieve it before use. Even though the grain is graded, transport generates dust which, once wet, clogs the gaps between grains: two passes through a fine sieve are enough. If you prefer, you can also rinse it.

When repotting, lay a layer of this grain on the bottom of the pot, over the drainage mesh, then continue with your chosen mix. Between the roots the material is settled with a chopstick, working from the bottom upwards to close the voids without crushing anything. Water generously the first time, until clean water runs from the holes.

Frequently asked questions

Does 3/8 mm pumice break down like akadama?

No. It is volcanic rock, not fired clay: the grain keeps its shape and porosity throughout the period between one repotting and the next, even after freeze and thaw cycles. That is the main reason it is chosen for substrates that need to stay open for a long time.

Can I grow a bonsai in pure pumice?

Yes, it is common practice during the establishment phase, when air around the roots matters most. Being inert it provides no nutrition, so feeding needs to be managed carefully and watering is more frequent than with a substrate containing moisture-retaining components.

How many pots will 5 litres cover?

It depends on the volume of the pots and how much pumice goes into the mix. Five litres is a modest supply, enough to fill a couple of medium-sized pots or to prepare the drainage layer for several seasonal repottings. If you are wondering where to buy pumice in a practical quantity, this is a convenient size to start with.

What is included

• Volcanic pumice, 3/8 mm grain size
• 5 litre pack

If you prefer to measure out the components yourself, you can put together your own mix on the made-to-measure soil page.