100% Pumice and Montezuma Cypress

[AaronThomas]

Okay… so I have read several posts on the subject of using 100% pumice… some dating back to 2013 and still can’t find a clear answer…perhaps there isn’t one. I found a thread where Ben aka Beng asked why not use 100% pumice as a substrate for some trees. Lots of great info and some great links provided by @JudyB and several others.

The reason I’m curious is because I currently have 7 Montezuma Cypress. 6 started last year and 1 started in 2017. 3 in 100% pumice, 3 in 50/50 Lava and fine orchid bark and one in the ground that is thriving but it doesn’t count.

The 3 in pumice are doing exceptionally well… lots of new growth and overall seem pretty healthy… I repotted 1 this season and there was a ton of new root growth. The other 2 have not been repotted this season.

The 3 in the lava/orchid bark mix are slow to push new growth… the two I started last year each have had a section of trunk that has died off and the one that was started in 2017 died at the top…. I will mention this is the tree that the kids chopped with what I originally was told was a freak frisbee incident but now have learned was a plastic Samurai Katana. None have been repotted this season.

I can’t imagine this is some sort of a coincidence… Other than the difference in substrates, I have treated each tree the same. Same watering schedule same feeding schedule same sun exposure.

Bad orchid bark? Each potted tree came from a different bag of bark... Not to mention the Elms don’t seem to mind it… Maybe something with MC and pine bark? Probably unlikely...

I guess this is a 2 part question... 1) Can I grow my MC in 100% pumice? Or a combo of pumice and lava? 2) What would cause the die back in the trees grown in the 50/50?

Sorry for the long winded question.

Thanks!!!

 

[AZbonsai]

I wondered who was cornering the AZ cypress market.

The reason I’m curious is because I currently have 7 Montezuma Cypress

 

[parhamr]

Yes, you can grow them in 100% pumice. Have you seen what they grow in natively? It’s clear they like a lot of water and nutrients. (I’ve typically seen them dwarved by growing in shallow sandy loam with about a 2" layer of fallen organic duff on the surface.)

I have one growing very well in pure pumice. Particles smaller than 1/16" were screened out. An acquaintance who collects them has a dozen or so like this. I believe Mirai uses pure pumice for them.

I’m not sure I know enough about them to guess about the dieback. If it was really chunky bark then maybe the roots had too much oxygen… their natural soils seem oddly anoxic. It could also be something about soil and water pH. I don’t think there’s much overlap in growing regions between pine and the false cypress.

 

[parhamr]

Wait a tic… you mean Taxodium mucronatum? Lol I was writing about Cupressus pigmaea. If so, disregard

 

[AaronThomas]

Taxodium mucronatum

Ah man! Yep... got me excited

 

[parhamr]

Ah man! Yep... got me excited

dammit

 

[AaronThomas]

Any other thoughts as to the die back? Or is it just shit bad luck...

 

[Leo in N E Illinois]

The beauty of pumice is that it is long term stable, it does not decay, it does not collapse, it has good air voids that stay open, essentially forever. Pine bark, fir bark, orchid bark, what ever the product is, begins decomposing the first day it gets watered. In time it collapses, it exudes organic compounds, it feeds mycorrhiza, (this can be good, can be not so good). Bark is a dynamic product whose traits change over time.

Perhaps the bark mix is too acidic or does not allow enough air penetration. Something about the bark is proving to be less than ideal.

Bark will have a nitrogen demand, in that the bacteria and fungi attaching the bark will feed off nitrogen in your fertilizer intended to feed the tree. They can out compete the tree. Trees in mixes heavy in bark need to be fed a high nitrogen formulation a little more frequently than the same species in an inert media like pumice. The nitrogen demand alone could account for the size difference. Usually we feed our trees more than they need, so the nitrogen demand effect does not become noticable. But if you have been light on feeding your trees, you would see the difference.

Of course, I am just speculating. I do not "know with certainty" what the problem is.

 

[AaronThomas]

@Leo in N E Illinois Thanks for the insight Leo. I typically repot every 2 years for the MC and feed 20-20-20 every week during the growing season. Too much?
Perhaps the orchid bark was changed a bit... the first tree did wonderfully the first few years... All went to pot this season.
I'm thinking I may just switch over to the 100% pumice or at least 50/50 with lava to be on the safe side.

 

[PiñonJ]

I believe Mirai uses pure pumice for them.

Ryan uses straight akadama for all coastal and wetland cypress (of whatever genus). Straight pumice is good for supporting new root growth, because it maintains air spaces (providing oxygen), which is why it’s popular for newly collected trees, but not as good for promoting fine ramification.

 

[River's Edge]

Any other thoughts as to the die back? Or is it just shit bad luck...

50%. organic means faster decomposition and higher moisture retention.Particle size of the bark and stage of decomposition will be critical. Would likely produce anaerobic conditions faster. Pumice holds moisture at a similar rate to Akadama so that percentage of bark seems very high to me! I raise my most difficult plants in pure pumice. The trickier collected trees.
Two drawbacks to pumice from my experience. 1. it is lightweight so trees must be secured in container well. 2. will dry out faster from evaporation due to irregular particle shape and firm structure. ( therefore I usually cover surface with light cover of shredded sphagnum moss!
Just comments from my personal experience. However I believe many serious collectors would echo these sentiments and add that their survival rate of collected trees increased dramatically when using pumice.
I use pure pumice in grow beds with excellent results, great substrate to host Micorrhyzae.

 

[AaronThomas]

Just comments from my personal experience.

Hi Frank... thank you for the information... makes perfect. Strange I’m suddenly having substrate issues ... but I’m excited about the pumice. Last season I sifted the dust and sandy fines and used partial sizes ranging from 1/32” to 3/16” in a 3” bed... only had to water 1 time a day. We shall see...
Think I will risk it and repot This week.
Thanks again

 

[AaronThomas]

not as good for promoting fine ramification.

Really? Why is that?

 

[PiñonJ]

Really? Why is that?

Because the coarse scale of a pumice substrate that will provide plenty of oxygen to an establishing root system will allow growth of coarse, or at least less ramified roots. I think a substrate like Boon mix (akadama, lava and pumice), which provides a good balance of water, oxygen and CEC, is physically more stable and has finer spaces that the roots have to grow through. Also, Ryan has a theory (for which I’ve seen evidence) that, as roots grow through particles of akadama, they actively decompose it into smaller particles, thus forcing finer root ramification.

 

[AaronThomas]

Because

Would you suggest pumice and lava? akadama may prove difficult for me to get.

 

[PiñonJ]

I don’t have this species. Maybe straight diatomaceous earth? What do you think, @Leo in N E Illinois ?

 

[River's Edge]

Because the coarse scale of a pumice substrate that will provide plenty of oxygen to an establishing root system will allow growth of coarse, or at least less ramified roots. I think a substrate like Boon mix (akadama, lava and pumice), which provides a good balance of water, oxygen and CEC, is physically more stable and has finer spaces that the roots have to grow through. Also, Ryan has a theory (for which I’ve seen evidence) that, as roots grow through particles of akadama, they actively decompose it into smaller particles, thus forcing finer root ramification.

This concern is based entirely on the source and quality of pumice. Seiving the particle size desired for root structure is needed regardless of the component chosen. Coairse Lava or Coarse Akadama will create larger root structure and less ramification of the roots as well.

 

[Adair M]

You have discovered for yourself the pitfalls of using bark. It does well for a while, then collapses when it decomposes.

mid you can’t get akadama, you can go 50/50 pumice/lava.The lava is heavier. So it helps with stability.

 

[River's Edge]

You have discovered for yourself the pitfalls of using bark. It does well for a while, then collapses when it decomposes.

mid you can’t get akadama, you can go 50/50 pumice/lava.The lava is heavier. So it helps with stability.

One other option for stability is granite grit. Readily available as chicken grit or turkey grit and graded by size! My regular Bonsai soil components are Akadama, Black Lava, Granite Grit and Pumice. The ratio is determined by the species and level of refinement. The particle size determined by the species and level of refinement, along with the overall size of the tree. Smaller trees and smaller pots generally use smaller particle size components. The amount of Akadama used depend on the preferred PH and water retention desired. This also applies to Kanuma when used for certain species such as Azalea. Kanuma has a lower PH than Akadama.

 

[PiñonJ]

This concern is based entirely on the source and quality of pumice. Seiving the particle size desired for root structure is needed regardless of the component chosen. Coairse Lava or Coarse Akadama will create larger root structure and less ramification of the roots as well.

the coarse scale...that will provide plenty of oxygen to an establishing root system

My point was that straight pumice is used (and particle size selected) to allow rapid establishment of a root system, not to create fine ramification. I don’t think you’re recommending that the OP use straight pumice, either.