I've done a 4:1 mix of screened composted wood mulch and turface. I though the mix was too moisture rententive for 2.25" plug pots but it worked great for lettuce in #1 nursery containers. When I unpotted them after harvest, the entire volume had been colonized by roots.

Yeah, diatomaceous earth is actually the preferred medium, and turface is the "when you can't find DE, this is close enough" substitute. When I say preferred medium, I'm speaking from a bonsai perspective, but bonsai soiless medium is pretty much the same thing as gritty mix at that point (as far as this is concerned).

Bruce, I was just reading your post in this thread. You mention screening out the particles less than 1/8". BE CAREFUL!! Remember you NEED at least some fraction of those particles in the 1/16" - 1/8" range for the mix to bind (and for retention). My mix calls for 1/2 part of bark in that range to be included, but that can be altered to increase the retention - if desired. Also, I'm seeing quite a bit of large diameter particles in your mix...beware of the ping pong balls dude! Are you passing it through a 1/2" mesh? If your product is comprised of too high of a concentration of larger particles...you may have to add another intermediate level of screening...say 1/4" to ensure that your larger pieces comprise only a moderate fraction of the total mix. Notice the amount of chips that are equal to or larger than your quarter? Quite a few, right? Notice mine. There are only a few pieces that are even half the size of the quarter. The more particles that you have in your mix that are similar, the better. You want to avoid too many large particles and too many small particles...the goldilocks zone is what your looking for....juuuuuust right. PJ

Figure the volume of all the pots, convert to cu ft. You'll get just under 3 cu ft of 5:1:1 ( for every 2 cu ft of PBFs + 4 gallons each of peat and perlite - or about 22 gallons. For every bag of Turface you buy (1-1/3 cu ft) & screen, you'll get just under 1 cu ft of screened Turface. Combine 1 cu ft of Turface with equal volumes of screened pine or fir bark + screened grit, you'll get about 2-3/4 cu ft of gritty mix. There are about 7-1/2 liquid gallons in a cu ft of material, so you'll get about 21 gallons. Since the grit has greater bulk density, you'll need more bags of grit vs Turface and fewer bags of bark at 2 cu ft/bag. Al