Thank you! This is really helpful! For a 16 inch pot how much bark fine (of course approximate) do you think we’d need? And do you think it’s okay to keep plants unpotted for a day or two while we track down more for mix

It is very approximate but most 16" diameter pots will hold about 22 quarts of potting mix so that would translate to about 15 quarts of bark fines. Give or take :))

Last question (and thanks for being so helpful): are bark fines different than mulch? It sounds like we need to tracj down former. Thank you!

Usually not the same......unless one can find very small bark mulch :-) The desired size of bark fines is 1/4 to 3/8 inch. You could go just a tad larger if needs must.

All my maples are in the gritty mix.

A palmatum "Yatsabusa"

A palmatum ^^^

A palmatum ^^^

Second step in a repotting session ^^^ - first being depotting the plant.

THIS ^^^ is a very healthy root system.

Gritty ^^^

5:1:1 ^^^

Appropriate bark for 5:1:1 at 3, 6, and 9 o'clock. If screened to remove fines, those 3 would be appropriate in gritty mix as well. The fir bark at top is what I use for the gritty after screening out the dust.

Because maples like or will tolerate more moisture in the medium than most other genera/species, the 5:1:1 is also a very good choice. I do think it's a rather ambitious undertaking to try to make things work on a rooftop, but perhaps your climate is more accommodating than here in Michigan.

Al

Thanks! Will these mini pine bark nuggets work in 5:1:1 mix — not sure if they are bark fines https://www.homedepot.com/p/2-cu-ft-Pine-Bark-Nuggets-B2PBL-SR/202526086?g_store=1225&mtc=Shopping-B-F_D28O-G-D28O-28_19_MULCH-MULTI-NA-Feed-LIA-NA-NA-BASE_SHP&cm_mmc=Shopping-B-F_D28O-G-D28O-28_19_MULCH-MULTI-NA-Feed-LIA-NA-NA-BASE_SHP-71700000062826514-58700005635612043-92700051386902121&gclid=EAIaIQobChMIuv3Umu2D6QIVioTICh2o6wi4EAQYAiABEgKMdvD_BwE&gclsrc=aw.ds

also how would one go about making a gritty mix —and what are it’s advantages?

Your maples look amazing btw!

Al and I could get into a bit of a back and forth here so just offering my observations :-)

The gritty mix is less water retentive so comes with a need to water more frequently. And it is heavy!! This could have an impact with a rooftop garden and a full sized containerized tree compared to a bonsai. Also with any need to drag the container in and out for winter care.

I grow some 3 dozen various JM's only in containers and am very happy with their performance in the 5-1-1. And even that soil mix with a large tree (not bonsai'd) in a large container, they are almost too heavy for me to move. My contractor partner is stopping by this week to help me schlepp my trees around, which I typically do at the start of every season. They remain outdoors untended all winter but I live in a very mild climate :-)

Pine bark fines for 511 is from dust to 3/8 inch. Since 3/8 sieve is hard to come by, a 1/2 inch hardware cloth for a sieve is good enough. So you will end up with dust to 1/2. In most cases this works unless the bark is heavily skewed towards smaller or larger sizes.

OK. I am also a newb for JMs in containers. I have a couple hard ones that are doing well in the ground for 6-7 years, but just starting with the container thing. Where should I start searching for bark fines?

I found some some bags of pine bark fines at our local ace hardware. :)

Al, that Yatsabusa is a thing of beauty. I found this thread because I have one on the way and I've FINALLY sourced the ingredients since moving to a different state. Thanks for the help during every phase of my gardening obsession the last 10 years, whether it was my orchid obsession, my euphorbia enthusiasm, or my maple madness (and, most recently and probably stupidly, my weeping cherry craze).

To the rest of the folks, I found bark fines a couple of places including pet store reptile bark (make sure it's the right size), local nurseries selling it as soil conditioner (definitely have to strain here), or if you're lazy and have money to burn there are some independent shops that sell it on Ebay, Amazon, and Etsy. As for the granite, a feed store locally is truly your best option, everything else is going to cost buku bucks. I can never find Turface anywhere except for the internet so I bite the bullet there and have that one just shipped direct to me.