Being new to Bonsai, I was wondering if someone could clarify soil particle sizes for me. After watching some Bonsai Mirai and reading the soil primer on RMBS web site, it seems to be that there are typically two ranges used: 1/8”-1/4” and 1/16”-1/8” and that generally everything that falls through a 1/16” screen is fines that is thrown away and everything that stays above a 1/4” screen is generally also not used in most soil mixes.
Am I understanding that right? If not, what is the upper limit of size when one talks about 1/4” particle size, as generally you sift for a range between two screens. It’s confusing (as a beginner) to talk about discrete sizes of particles like the RMBS soil primer does, since it seems more common to sift between screens and have a range of particle sizes.
I got further confused when I opened the pumice that arrived via the club order and found that it is all extremely large and maybe only 10% of the bag falls through a 1/4” screen. Mostly seems unusable to me, unless I’m just way off base in my understanding of these particle sizes. The lava that arrived fell 95% between the 1/4” screen and 1/8” screen and is more along the lines of what I was expecting.
Thanks!
Thank you so much for the reply! I've also saved some of these 1/4-3/8" particles for aeration layer on some of my trees, but these particles in the recent club order seem to be largely in the 3/8"-1/2" range. I will try to pulverize as you suggested -- do you have any tool/technique suggestions to make that easier?
Hey Matt: good questions. Agree that you have the soil particle range correct. Everything that falls through 1/16" should uniformly be discarded. Particles captured on top of the 1/16th screen are left in mix for water loving species and small bonsai. If particles stay above 1/4" screen, they are generally left out with some caveats:
Very large bonsai, especially pines could tolerate there particles that are just over 1/4". I often retain these larger particles for the bottom "aeration" layer as well (see Ryan Neil, Bonsai Mirai).
If you are finding that a lot of the pumice you have is >1/4" (ie: won't pass through this screen) and you have modest or moderate size trees, I would advise to pulverize it to some degree and resift it. You're mostly looking for the size that passes through the 1/4" screen and is captured above the 1/8"
Hope that helps!