I have a bonsai ficus that may need repotting; however, I do not have any specialized bonsai soil, and in the pandemic environment I'm not sure I could get hold of any. (I know the nearest nursery is closed due to the virus.) Can I approximate an acceptable potting mix with stuff from the local home center? I know that basic potting soil won't do, but could I mix together a few things and come up with something reasonable?
This topic has been much discussed in Bonsai circles producing a wide variety of opinions. The goal is to have something with very sharp drainage but at the same time to hold enough nutrient-carrying moisture to keep the Bonsai growing comfortably without excess.
A material such as turface, used on playing fields so that in rain downpours the surface becomes playable very quickly, provides that sharp drainage since it is baked hard and is quite widely available. But this means it can only carry moisture on its surface and needs to be mixed with other more absorbent materials or you are constantly watering. In addition turface is problematic since if you mix in too high a proportion of it, when you pull the plant from the pot the whole root ball falls apart since there is nothing to bind it together.
Vermiculite holds moisture so could be your water retaining additive. Perlite is also quite widely obtainable and this also helps with water availability. Peat is more of a binder, and activated charcoal is another possibility but with this the quality is important since some charcoals do not work very well in plant soils.
So experiment a bit with what you can get in small quantities and report back your findings?