Slab planting never repotting - can't wrap my head around this

The last live stream creating the composition of the two Picea pungens planting on a Jan Culek upside-down slab was fantastic. I totally love the final result and I am eager to experiment with the use of sphangnum moss for the wall. However, Ryan mentioned that unless there are problems or design changes, he does not plan to ever repot the trees. The trees still contain field soil and that means never fully transitioning to 100% modern substrate. Somehow it seems to fly against all that we hear, even at Mirai. I can imagine that at some point all the akadama in there will have disintegrated and the root mass be so thick that it will affect negatively the balance of H2O and O2. Any thoughts? I will try to ask this on the next Q&A but perhaps others here in the forum have some input to share.


He doesn’t re-pot, but he does re-work the root mass. When the soil performance degrades, he’ll clear space under the root mass against the slab with a chopstick and introduce new akadama into the space.


So… all the work is done on the shin? I thought that the health of the tree relies on a well ramified shin.
I leave my slab plantings much longer that potted forests.

No, not the shin specifically, just enough space over the slab to replace some of the soil.

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Just came across this post, coincidentally I also just watched the new slab planting maintenance stream. Have you checked that out yet @rafi? It may answer some of your questions here.

Yes I just watched it today. I still don’t understand how you’d be able to maintain health in the shin without ever reporting. There must be some major differences in the life expectancy of a tree in a slab or rock planting compared to a pot and also likely a much lower growth rate after all available space for roots gets occupied.

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Hi Rafi
I suspect that because the soil is different the tree acts differently. I know the soil I grow my penjing in grow differently, slower even and as roots die because there is bacteria and micorrhiza they are reabsorbed,
Cheers Adam