Michael Hagedorn on 100% pumice soil

[Brain Treez]

His most recent blog post is in line with my experience this past year using either 100% or 75%+ pumice, though I have boxwoods and junipers instead of maples. Granted, like him I also live in the PNW and am fortunate to have such a great growing climate and access to dirt cheap pumice.

I'm going to try leaning even further into all or majority pumice this repotting season.

 

[Ruddigger]

We use black lava here instead of pumice, but it also works very well. Theyre both volcanic rock, so it’s not surprising. Lava has the benefit of being a heavier so it doesnt wash away as easily, and the dark color looks pretty nice in the pot as well.

 

[Brain Treez]

We use black lava here instead of pumice, but it also works very well. Theyre both volcanic rock, so it’s not surprising. Lava has the benefit of being a heavier so it doesnt wash away as easily, and the dark color looks pretty nice in the pot as well.

I also appreciate that this can help people realize akadama isn't the end all, be all, of substrates. Trees can grow just fine in other stuff! People shouldn't worry they're handicapping their trees because they don't use akadama (whether because of cost or carbon footprint reasons).

 

[Ruddigger]

I also appreciate that this can help people realize akadama isn't the end all, be all, of substrates. Trees can grow just fine in other stuff! People shouldn't worry they're handicapping their trees because they don't use akadama (whether because of cost or carbon footprint reasons).

It really depends what you want out of the tree. My teacher David Nguy uses about 70% black lava and 30% akadama. I use 50/50 or even 25/75 for some deciduous when I want tighter ramification. You can adjust the density of your branching with increased akadama.

 

[BrightsideB]

I notice people in hotter climates leaning towards lava and people in wet or humid/wet climates using pumice. Or is that just me? I’ve had some problems using heavy lava mix with deciduous and find pumice really works better for me. But it’s also what is more available and affordable to an individual.

 

[Bonsai Nut]

I notice people in hotter climates leaning towards lava and people in wet or humid/wet climates using pumice. Or is that just me? I’ve had some problems using heavy lava mix with deciduous and find pumice really works better for me. But it’s also what is more available and affordable to an individual.

When I lived in Southern California, my mixes tended to use a lot of pumice. Due to the extremely low humidity I often had to water twice daily, and mixes that contained too much organic matter tended to hold too much water in the interior of the rootball - while the exterior would dry out. I needed mixes that would absorb water uniformly, without remaining saturated.

 

[Goodbrake]

I notice people in hotter climates leaning towards lava and people in wet or humid/wet climates using pumice. Or is that just me? I’ve had some problems using heavy lava mix with deciduous and find pumice really works better for me. But it’s also what is more available and affordable to an individual.

This might just be that areas with cheap access to pumice happen to be wetter. Back when I lived in CA, pumice was cheap and you could buy it everywhere. In TX, if I want it I have to get it shipped in. I haven't found a cheap source for it out here so I've been using more perlite in its place.

 

[Cadillactaste]

I've wondered that... if pumice was so good for newly collected trees. Why it was then switched over for our medium.

Interesting read in the link. I had wondered about refined roots...and he touched on that too with the finer top dressing and smaller particles of pumice.

 

[jevanlewis]

I am in a dry climate and I am now using 100% pumice for my pines. Of course, all are in development; once in refinement, I probably will switch to more akadama. Also, I am able to water two or three times a day if needed during the hottest summer days. I was using 50-50 pumice and lava, but the lava has to be sifted on site at a landscape supplier, while high-quality, bonsai-appropriate pumice is available "locally" (2 hours away) for only $23.50 for a 45-lb bag. So, due to my laziness, I've shifted the lava portion of my mixes to pumice.

My pines have been extremely healthy in 100% pumice. But, I would like to see more surface roots than I have been seeing, which might be caused by the surface layer drying out too quickly. To attempt to get more surface roots, last growing season I started:

1. Lifting the pots (Anderson flats) off the ground. Before, the roots tended to grow down and into the ground rather than populating the surface of the pot.
2. Adding sifted sphagnum moss to the top layer of soil.

My maples are in 50% pumice and 50% pine bark, and have zero issues with being too dry (or too wet). Even in my dry climate, I wouldn't be too worried about putting the maples in 100% pumice given they are in development (i.e., larger pots than refinement/show pots) and because they get afternoon shade, preventing them from drying out too fast.

 

[19Mateo83]

I switched to 100% pumice in my pines and junipers last year. Growth has been way better than in an organic mix. I honestly can’t wait to see the roots in a year or two. I kinda want to try the maple/thick sphagnum like in the article on some JM material and see if I can get similar results like in the article.

 

[pandacular]

I was looking at one of the maples that he shows in his post just today—roots popping out of the soil!

One thing that I mentioned to him was that without consistent release fertilizer—they use osmocote and a Dosatron injection system—it might be hard to replicate the results.

 

[badatusernames]

We use black lava here instead of pumice, but it also works very well. Theyre both volcanic rock, so it’s not surprising. Lava has the benefit of being a heavier so it doesnt wash away as easily, and the dark color looks pretty nice in the pot as well.

How do you know when to water? I put a succulent in 100% lava once and killed it due to underwatering (desert rose).

I can't imagine lava absorbs much water but I've always been interested when I hear of folks growing in 100% lava. Someone on (I think @Maiden69 ?) has told of a choujbai artist in Japan who grows his seedlings in 100% lava.

Always assumed you'd need to be in a really humid environment to pull that off.

Also, it seems to be rather hard for me to find pumice OR lava that matches medium grain akadama, but that's an unrelated topic...

 

[badatusernames]

When I lived in Southern California, my mixes tended to use a lot of pumice. Due to the extremely low humidity I often had to water twice daily, and mixes that contained too much organic matter tended to hold too much water in the interior of the rootball - while the exterior would dry out. I needed mixes that would absorb water uniformly, without remaining saturated.

Interesting. I've been wondering about that a lot because I've become pretty enamored by white pines. I keep a chopstick in the root ball to see when it's getting dry but it can take a long time - and I don't know what that means for the rest of the root mass, where the soil has obviously become much dryer. Knowing that white pines prefer to dry out a bit, I've been trying to figure out how best to balance this.

I just put a white pine in a big, deep grow box and am particularly curious how I'm going to manage that.

Wish Adair was still here, seemed to be a well of information for white pine.

 

[RJG2]

Wish Adair was still here, seemed to be a well of information for white pine.

 

[Ruddigger]

How do you know when to water? I put a succulent in 100% lava once and killed it due to underwatering (desert rose).

I can't imagine lava absorbs much water but I've always been interested when I hear of folks growing in 100% lava. Someone on (I think @Maiden69 ?) has told of a choujbai artist in Japan who grows his seedlings in 100% lava.

Always assumed you'd need to be in a really humid environment to pull that off.

Also, it seems to be rather hard for me to find pumice OR lava that matches medium grain akadama, but that's an unrelated topic...

Lava holds water really well, actually. There are many professional growers and bonsai artists that use pure lava, including Ed Clark and Adam Toth. Knowing when to water isnt an issue.

 

[Sansokuu]

How do you know when to water? I put a succulent in 100% lava once and killed it due to underwatering (desert rose).

I can't imagine lava absorbs much water but I've always been interested when I hear of folks growing in 100% lava. Someone on (I think @Maiden69 ?) has told of a choujbai artist in Japan who grows his seedlings in 100% lava.

Always assumed you'd need to be in a really humid environment to pull that off.

Also, it seems to be rather hard for me to find pumice OR lava that matches medium grain akadama, but that's an unrelated topic...

Adeniums (desert rose) in the growing season really love water and humidity, but you need high temps. I don’t know if pure lava would work it drains too much, you would have to water pretty often. They are considered tropical plants not quite a desert type succulent. Once dormant though and below 60 degrees, no watering. For adeniums I used a mix of pumice and no peat cactus mix from California Cactus Center, I probably underwatered mine but basically when the soil dried out it would get watered. I’m no expert but my parents still have my adenium that I got 20 years ago.

 

[pandacular]

Knowing when to water isnt an issue.

unfortunately, the issue is simply of skill, which i only say as someone without the skill. i am fortunate to get to watch a few teams of pro water in their gardens which is incredibly informative.

 

[MaciekA]

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.

Lots of pieces to this puzzle and Michael is a details guy! Even shade cloth factors into all this.

 

[The Barber]

I've wondered that... if pumice was so good for newly collected trees. Why it was then switched over for our medium.

Interesting read in the link. I had wondered about refined roots...and he touched on that too with the finer top dressing and smaller particles of pumice.

Akadama works well for encouraging root division better than lava or pumice is my understanding of it.

 

[jevanlewis]

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.

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