Kiryuzuna conifer bonsai soil - 2/5 mm grain - 14 lt bag

What it is and where it comes from

Kiryuzuna is a Japanese soil of mineral origin, ochre-yellow flecked with grey. It comes as pre-sieved granules, here in the 2/5 mm size, packed in the original 14-litre bag. It is a famously iron-rich material, and that is the main reason conifer growers always keep some in stock.

How it behaves in the pot

It drains. That is the first thing you notice when watering a pot made up with kiryuzuna: water passes straight through the substrate without stagnating, and air flows back immediately into the spaces between one granule and the next. The roots find oxygen and stay short and well ramified, a condition that matters more on conifers than on any other group of plants.

The granule is hard and does not collapse after the first frosts, so the substrate stays open from one repotting to the next instead of turning to mud. The iron content and the mineral structure encourage the development of mycorrhizae, the fungi that live in symbiosis with the roots and which on pines can be seen with the naked eye as a whitish felt on the root ball. The pH, between 6.5 and 6.8, stays close to neutral.

Features

• Japanese soil of mineral origin
• Grain size 2/5 mm
• 14-litre bag
• pH between 6.5 and 6.8
• Iron-rich material, high in micronutrients
• Encourages the development of mycorrhizae

Which grain and for which plants

The 2/5 mm is the general-purpose size: it works well in the body of the substrate for medium-sized bonsai and also suits small pots and shohin, where a coarser granule would leave too many voids beneath the roots. On large specimens it is gladly used in the upper part of the pot, keeping coarser material at the bottom. The 14 litres in the bag are enough for a repotting session on several plants without having to ration the material.

The classic use is on conifers: pines, junipers, yews, spruces. Many people use it on its own precisely on pines; alternatively it pairs well with akadama, which brings water retention where kiryuzuna offers little. Anyone looking for a soil for ficus bonsai or other indoor broadleaves will find a base with greater retention more suitable, keeping kiryuzuna as the draining component.

How to use it when repotting

First of all, sieve it. Even a pre-screened material produces dust during transport, and that dust will clog the pores of the substrate within a few waterings: a fine-mesh sieve and a couple of shakes over a bucket are all it takes. The bottom of the pot is covered with a layer of coarser material, over the drainage mesh.

Once the kiryuzuna has been spread around the root ball, work it down between the roots with a wooden chopstick, moving from the bottom upwards, without pressing with your fingers: the hard granule does not compact by itself and the voids will remain if you do not fill them. Then water generously until the water runs clear from the drainage holes.

Frequently asked questions

Can kiryuzuna be used pure? Should I use this on its own?

On conifers yes, many growers use it alone and obtain dense root systems. Bear in mind, though, that it holds little water: in summer, with small pots and hot weather, watering becomes more frequent. Mixed with akadama, the water balance evens out.

Why is it recommended specifically for pines and junipers?

Because it is an iron-rich material that stimulates the development of mycorrhizae, the fungi that live symbiotically with conifer roots. Add to this the fast drainage that pines and junipers appreciate, and a pH between 6.5 and 6.8 that does not upset the balance of the substrate.

Is the 2/5 mm grain suitable for a small pot?

Yes. The 2/5 mm is a medium size that works well both in shohin and on medium-sized bonsai, because it fills the space between the roots without leaving overly large air pockets. On large specimens it is best reserved for the upper part of the pot.

What's included

• Japanese kiryuzuna, 2/5 mm grain
• 14-litre bag

Anyone who prefers to measure out the components themselves can put together their own mix on the made-to-measure soil page.