Ahh, soils. First off, I live in a pretty small microcosm and have no interest in promoting any techniques. I have not been trained on this--its not hard. I only grow what I grow--and as far as slabs that is pretty much larch and white cedars, which are not picky about life on a slab. Forests grown on slabs are a lot of work to be kept nice--so beware. Here is my take on slab growing trees.
*I assemble trees I assume are not going to need to grow much--or if they do need any development it would be fine.
*I always grow them first in a shallow box or on plywood and achieve a dense, solid, thin mat of roots.This is the most important. Don't unnecessarily tear it apart.
* I use unremarkable, old fashion, fine (retained on 1/16"+ screen) with some fine/med (retained on 1/8" screen) piled here and there, durable soil with about 25%(or more) organic (pre-moistened, sometime inoculated with myco and a wetter ) usually graded decomposing bark nodules. The aggregate portion is a blend of mostly Turface or whatever, sometimes with Perlite or small amounts of small lava, pumice or Haydite or granite (I mostly quit using granite for anything). The majority of the added soil is just tucking soil--the root mat itself contains most of the soil so be sure it is a quality finer soil.
* Everything is mossed and I maintain this--important.
* Thin the moss if it gets over dense.
*Sometimes moss declines seasonally or otherwise--don't freak--be patient--wait--add moss if necessary.
*Try to keep moss off the trunks.
*Keep the root pad thin.
*Sometimes I get by by tying things down over and around the slab.
*Sometimes I use chunks of wire to space and hold trees.
*Sometimes I add tie downs when I am planting--if i do I try to epoxy in small hoops of ss wire then add a tie down wire.
*Fertilize very little and usually only later in the season--if you fert a lot then you have to do root work a lot which is a mega-pain and unnecessary and defeats the whole mode.
*RP (major lifting, root thinning and soiling) every 10 years or so, or never--in the interim, infrequently cut holes or sections of the mat out and refresh the soil.
*Much ado is made about retainer wall construction--really its no big deal--I have made stick clay much using pottery clay or Betonite clay or mud and adding long fiber sphagnum or hair or whatever. Use some used fine soil stolen from another tree--I always do this to some extent. Or chunks or strips of cut-off root mat with mud smeared on them--then moss, moss, moss--and fix the moss. Then keep damp.
*Drainage is not important unless there is a huge dip in the slab--even then the established plants drink it up. Healthy trees can be and are cultivated on shallow non draining slabs.
* Keep moist always--water differently--protect from afternoon sun.(my slab plantings are always moist under the moss) if in doubt, water.
*Little slabs work way different and drying can be a big deal.
*Good water quality is important with long term plantings.
*I assemble trees I assume are not going to need to grow much--or if they do need any development it would be fine.
*I always grow them first in a shallow box or on plywood and achieve a dense, solid, thin mat of roots.This is the most important. Don't unnecessarily tear it apart.
* I use unremarkable, old fashion, fine (retained on 1/16"+ screen) with some fine/med (retained on 1/8" screen) piled here and there, durable soil with about 25%(or more) organic (pre-moistened, sometime inoculated with myco and a wetter ) usually graded decomposing bark nodules. The aggregate portion is a blend of mostly Turface or whatever, sometimes with Perlite or small amounts of small lava, pumice or Haydite or granite (I mostly quit using granite for anything). The majority of the added soil is just tucking soil--the root mat itself contains most of the soil so be sure it is a quality finer soil.
* Everything is mossed and I maintain this--important.
* Thin the moss if it gets over dense.
*Sometimes moss declines seasonally or otherwise--don't freak--be patient--wait--add moss if necessary.
*Try to keep moss off the trunks.
*Keep the root pad thin.
*Sometimes I get by by tying things down over and around the slab.
*Sometimes I use chunks of wire to space and hold trees.
*Sometimes I add tie downs when I am planting--if i do I try to epoxy in small hoops of ss wire then add a tie down wire.
*Fertilize very little and usually only later in the season--if you fert a lot then you have to do root work a lot which is a mega-pain and unnecessary and defeats the whole mode.
*RP (major lifting, root thinning and soiling) every 10 years or so, or never--in the interim, infrequently cut holes or sections of the mat out and refresh the soil.
*Much ado is made about retainer wall construction--really its no big deal--I have made stick clay much using pottery clay or Betonite clay or mud and adding long fiber sphagnum or hair or whatever. Use some used fine soil stolen from another tree--I always do this to some extent. Or chunks or strips of cut-off root mat with mud smeared on them--then moss, moss, moss--and fix the moss. Then keep damp.
*Drainage is not important unless there is a huge dip in the slab--even then the established plants drink it up. Healthy trees can be and are cultivated on shallow non draining slabs.
* Keep moist always--water differently--protect from afternoon sun.(my slab plantings are always moist under the moss) if in doubt, water.
*Little slabs work way different and drying can be a big deal.
*Good water quality is important with long term plantings.
