Here is a pretty good comparison of which materials do what in solarization.
http://www.waynesthisandthat.c...
I have used mainly cardboard, black plastic and clear plastic. The main reason for using clear plastic is the depth of treatment--I am trying to kill a bad infestation of Asian wisteria. the roots, like kudzu, go deep into the soil, and then pop up all over the place. All know if I see any shoots next summer, but it looks like the clear plastic plus HOT weather in full sun is working. In other areas I use cardboard--but wisteria roots, and also ivy will come up through the cardboard. It has constantly to be renewed so it is not a permanent solution--at least against the woody vines Im trying to get rid of.
As for beneficial flora, you want the beneficial flora that goes with the plants you will grow later--not the flora that has been colonized by the weeds and favors those. It might be a good idea to put in a fall cover crop to recondition the soil after solarization.
PS. If you've ever had a round of antibiotics and wound up with a queasy stomach--you have a good notion of what soil is like that has been depleted of microflora! Probiotics for us, mycorrhizae for the soil!
