Michael Hagedorn on 100% pumice soil

[radhatter]

not scientific, just a personal experiment. Last year I planted a blue atlas cedar in pure pumice from the PNW. Likely the same stuff Michael used. This was without the top dressing in a shallow container. Results were poor. The tree lagged behind another potted in a mix of 60% pumice 40% compost. Some fine root growth was observed but nothing exceptional. I’ve observed good results with pumice in other experiments with collected trees which is why I tried this but I think that top dressing of moss to help keep in more moisture may be essential to success with pumice. That being said, one example is not a rigorous study. I’ll probably give it a shot with top dressing this year and see how that goes.

 

[Gabler]

not scientific, just a personal experiment. Last year I planted a blue atlas cedar in pure pumice from the PNW. Likely the same stuff Michael used. This was without the top dressing in a shallow container. Results were poor. The tree lagged behind another potted in a mix of 60% pumice 40% compost. Some fine root growth was observed but nothing exceptional. I’ve observed good results with pumice in other experiments with collected trees which is why I tried this but I think that top dressing of moss to help keep in more moisture may be essential to success with pumice. That being said, one example is not a rigorous study. I’ll probably give it a shot with top dressing this year and see how that goes.

Also, faster growth isn't the goal. We already know the absolute fastest growth will be in something like 100% decomposed kitchen compost. It has what plants crave. The benefit of pumice and akadama is the type of growth.

 

[radhatter]

Also, faster growth isn't the goal. We already know the absolute fastest growth will be in something like 100% decomposed kitchen compost. It has what plants crave. The benefit of pumice and akadama is the type of growth.

That’s fair. In this instance it was complete stagnation with little root growth and pale color vs new buds and bright healthy foliage. I also know there are many reasons that could account for the difference. Just my experience that may help out other nutters with their own experiments

 

[Ruddigger]

Michael undersells the following point a bit in the post but, in person, he has been making it for years:, i.e. that pumice provenance actually matters a great deal and can account for different observed performance of "pumice" in different parts of the US.

There are noticeable differences in pumice even within the northwestern US, for example between Oregon pumice and Idaho pumice (Hess mine). Japanese pumice is very different looking from the Oregon stuff as Michael has mentioned. The Hess mine stuff has a non-trivial quantity of obsidian in it and looks quite different (much whiter) when totally dry. When I tried the Hess mine stuff 5 years ago, Michael warned me that I might not like it as much as the local stuff.

I think we do ourselves a (mild) disservice when we treat pumice as a monolith (pun intended I guess), but given that many obtain it in a way that obscures the source (especially if shipped instead of picked up at a local aggregate supplier), I think it makes some sense we haven't been able to wrap our heads around it yet.

Even lava/scoria has some similar provenance issues. For example, the previously-discussed unwanted (boron I think?) toxicities in some (but not all) Oregon-collected lava. Meanwhile, other lava causes no issues for growers. I have similar results as @Ruddigger in that my (non-Oregon-sourced AFAIK) lava holds a lot of water and is impressively hefty when wet (which I like, because it also seems to hold lots of air), but the stuff collected from the cinder cone in the Cascades (a common directly-collected source of lava for people around here) seems to hold less water than my out-of-state sourced stuff. They look noticeably different from one another but are both undeniably and clearly scoria. Unfortunately, I don't know where my out-of-state stuff came as it was ordered online. But there are differences.

Side note, @Cadillactaste mentioned surface roots above. Something that is common teaching within Hagedorn's sphere of influence (students / apprentices) -- top dressing goes on damn near everything, including conifers. IMO, top dressing (not just the precise way in which it is done, but also the lack of fear of top dressing) and specific watering practices (do it like the teacher says or the warranty is void) are a huge influence over the observed performance of any soil used by this group of people. I'll just say for @Ruddigger 's benefit that I have found some really nice short-fiber moss that will reliably (albeit slowly) colonize scoria. Going back to pumice (and adding the possible confounding factors of pumice provenance), whenever people on the west coast (esp central valley and SW regions) report extremely rapid top-drying of pumice, I always wonder what their top dressing practices are, if any. Michael teaches multiple top dressing techniques -- not just moss, but as @Cadillactaste mentions, also shohin-sized akadama/pumice.

A well thought out response. I too top dress everything, and have no problem growing moss, even in full sun.

 

[radhatter]

That’s fair. In this instance it was complete stagnation with little root growth and pale color vs new buds and bright healthy foliage

A well thought out response. I too top dress everything, and have no problem growing moss, even in full sun.

What are y’all top dressing with? Chopped sphagnum moss? Local collected moss?

 

[Gabler]

What are y’all top dressing with? Chopped sphagnum moss? Local collected moss?

I top dress with chopped sphagnum moss with a little bit of live moss mixed in. The goal is for the live moss to eventually replace the sphagnum moss. Ryan Neil says that if you just cover the pot with a sheet of moss, the soil won't breathe as well. I don't know if that's true, but I think it looks better if the moss grows on its own than if you just squish clumps of it together across the surface. It avoids the jigsaw puzzle look.

 

[Ruddigger]

It has what plants crave.

It’s got electrolytes…

 

[PowerTap]

What are y’all top d

In the PNW, if I stopped moving long enough I'd grow top dressing.

 

[19Mateo83]

Also, faster growth isn't the goal. We already know the absolute fastest growth will be in something like 100% decomposed kitchen compost. It has what plants crave. The benefit of pumice and akadama is the type of growth.

 

[radhatter]

In the PNW, if I stopped moving long enough I'd grow top dressing.

Yes, this has been observed in many of my trees

 

[pandacular]

An air layer we separated today, which ended up in pure pumice. Michael has reason to believe that top dressing is especially important in pumice, but it only goes on the new soil, not the core of the root ball.

 

[Wood]

@pandacular was Michael using pure pumice for the air layering medium or something else?

And does anyone have a good source for the high quality pumice instead of the Idaho/Hess mine stuff?

 

[pandacular]

no, the air layer was his usual mix of 50/50 pumice and akadama. After separating the layer, he had me put it in 100% pumice, partly to continue experimenting.

 

[BrightsideB]

no, the air layer was his usual mix of 50/50 pumice and akadama. After separating the layer, he had me put it in 100% pumice, partly to continue experimenting.

Are you doing an apprenticeship? That airlayer is nice!

 

[pandacular]

Are you doing an apprenticeship? That airlayer is nice!

No, just a student in his seasonals! I highly recommend it if you are able.

 

[Brain Treez]

Good points. The Idaho pumice is much whiter than the pumice I purchased from Bonsai Jack a couple years ago (and whiter than the pumice I purchased locally when I lived in Seattle). The Idaho pumice is also 10% heavier, but that could be due to the aggregate size of the Idaho pumice being smaller and more uniform, and therefore there are smaller air pockets. Also, the Idaho pumice seems to have a smoother surface. @MaciekA Other than color, are there any other things Michael warned that you might not like about the Idaho pumice vs. the Oregon pumice?

Left = Bonsai Jack (location of source unknown)
Right = Idaho

View attachment 585173

Well, this is interesting. The pumice I get from a local landscape supplier appears to be a match for the Idaho pumice. Why the hell are they buying that stuff when Bend is so much closer? Hmm.

 

[defra]

i read multiple examples of people that also use 100% pumice with good results for years so i am not suprised by this
ive not used pumice pure myself so far but might try it with some test plants, my only worry is that it holds less water then my current mix and that might be a downside in summer for me but ill give it a go with some seedlings to compare

 

[MaciekA]

In the PNW, if I stopped moving long enough I'd grow top dressing.

A couple years back, I got lazy with clearing the needle duff out of the bottom of my car's windshield. This particular car was being driven a lot less that year, so it sat a bit, and the first time I drove it that spring, I discovered a dozen Japanese maple seedlings growing in the needle duff in the corner of my windshield. (edit: I've kept it clean since, but FWIW, I can say japanese maple really really loves to germinate in cedrus atlantica needle duff).

A parked Subaru in the PNW will acquire "top dressing" that can become a bonsai ("Subaru Forester Touring as a bonsai pot" also feels like a very PNW thing to say.. -- Japanese pot, too).

 

[MaciekA]

i read multiple examples of people that also use 100% pumice with good results for years so i am not suprised by this
ive not used pumice pure myself so far but might try it with some test plants, my only worry is that it holds less water then my current mix and that might be a downside in summer for me but ill give it a go with some seedlings to compare

One interesting thing about this is that many of the all-pumice (or all-volcanics) growers (including the author of the blog post + students) are in a climate (Willamette Valley) that has a baking-hot paper-dry summer in comparison with the Netherlands. It is true, surface evaporation is going to be fast, but pumice holds a lot of water in terms of actual volume. You can solve surface evaporation the way Hagedorn and his students solve it -- using top dressing and sun exposure control. Then you have a high-water capacity soil that also wastes no space. Clean breathing roots can fill all of the space and reach the maximum water uptake volume the pot can hope for.

One assumption that is baked into Michael's post: For some level of serious practitioner and/or "serious professionally-worked tree I wouldn't want to lose", there is the assumption that the owner/grower has ensured someone will be near the tree all day every day during the hot months of the summer. This is specifically true for the author of the blog post and many of his students. IMO one of the main dividing lines in many bonsai debates should be "is someone with the trees all summer yes/no", i.e. commuting distance dictates maximum attainable root ramification / volume efficiency. A thirsty tree has a short leash.

With that assumption granting someone always there to water, the priority shifts from "how much water can the soil hold" to "how much fine rootage can the soil support", because achieving maximum fine root density for the pot volume gives you maximum water rate of uptake. This is important if you can expect 35 to 47C and 15-25% humidity for weeks on end, trees move water very fast in summers like that. Rate of uptake is more important than storage capacity in that case with that always-on-site assumption. The PNW's cooler summertime nights don't even matter, because a broadleaf deciduous tree can draw all of the moisture out of a pot in less than 2 hours in a properly hot Oregon day.

Hagedorn and his apprentices/students are growing things like maples, birch, cottonwoods, corylopsis, mountain hemlock, alder, etc etc in pure pumice or pure akadama or pure perlite or combinations thereof, with zero organic additives, in a summer that gets 35 - 47C highs with lunchtime humidity levels that can easily start wildfire. They keep those sensitive species well-ramified in the roots and canopy in spite of this. They can pursue that lower-compromise setup because:

- Overhead shade cloth
- Someone is always there to water
- Live top dressing done specifically the way Hagedorn does it (thin shredded, pressed in carefully, inoculated with neighborhood moss, etc, kept cleaned up and rejuvenated seasonally)
- Watering methods (first pass, second pass, finger-touch testing, etc etc)

If you are in a climate that has strong dryness in the summer, this solution fits together like a puzzle. People will get different results if they aren't doing a copycat of the post author.

Given my success with getting moss onto lava, I wonder if people using something which is not pumice but still porous/granular may see improved moisture and near-surface rooting results from (expertly-applied) top dressing (+ overhead shade cloth for intensity control as well) -- no switch to pumice required in those cases.

 

[defra]

One interesting thing about this is that many of the all-pumice (or all-volcanics) growers (including the author of the blog post + students) are in a climate (Willamette Valley) that has a baking-hot paper-dry summer in comparison with the Netherlands. It is true, surface evaporation is going to be fast, but pumice holds a lot of water in terms of actual volume. You can solve surface evaporation the way Hagedorn and his students solve it -- using top dressing and sun exposure control. Then you have a high-water capacity soil that also wastes no space. Clean breathing roots can fill all of the space and reach the maximum water uptake volume the pot can hope for.

One assumption that is baked into Michael's post: For some level of serious practitioner and/or "serious professionally-worked tree I wouldn't want to lose", there is the assumption that the owner/grower has ensured someone will be near the tree all day every day during the hot months of the summer. This is specifically true for the author of the blog post and many of his students. IMO one of the main dividing lines in many bonsai debates should be "is someone with the trees all summer yes/no", i.e. commuting distance dictates maximum attainable root ramification / volume efficiency. A thirsty tree has a short leash.

With that assumption granting someone always there to water, the priority shifts from "how much water can the soil hold" to "how much fine rootage can the soil support", because achieving maximum fine root density for the pot volume gives you maximum water rate of uptake. This is important if you can expect 35 to 47C and 15-25% humidity for weeks on end, trees move water very fast in summers like that. Rate of uptake is more important than storage capacity in that case with that always-on-site assumption. The PNW's cooler summertime nights don't even matter, because a broadleaf deciduous tree can draw all of the moisture out of a pot in less than 2 hours in a properly hot Oregon day.

Hagedorn and his apprentices/students are growing things like maples, birch, cottonwoods, corylopsis, mountain hemlock, alder, etc etc in pure pumice or pure akadama or pure perlite or combinations thereof, with zero organic additives, in a summer that gets 35 - 47C highs with lunchtime humidity levels that can easily start wildfire. They keep those sensitive species well-ramified in the roots and canopy in spite of this. They can pursue that lower-compromise setup because:

- Overhead shade cloth
- Someone is always there to water
- Live top dressing done specifically the way Hagedorn does it (thin shredded, pressed in carefully, inoculated with neighborhood moss, etc, kept cleaned up and rejuvenated seasonally)
- Watering methods (first pass, second pass, finger-touch testing, etc etc)

If you are in a climate that has strong dryness in the summer, this solution fits together like a puzzle. People will get different results if they aren't doing a copycat of the post author.

Given my success with getting moss onto lava, I wonder if people using something which is not pumice but still porous/granular may see improved moisture and near-surface rooting results from (expertly-applied) top dressing (+ overhead shade cloth for intensity control as well) -- no switch to pumice required in those cases.

Yeah my current mix already suits my needs and also proven to het similar results.
As you mention i cant be home 24/7 and bonsai is my hobby and it doesnt generate money for me and so i have a full time job to do so some days i can water them before going to work and then again when i get back so without shade cloth or other things to orotect them during hot summer days there might be my challenge when using pure pumice but maybe its more water retentive as i think so ill try ut out with some seedlings