Thanks Robert for posting this information. It made me more confident I was doing the right thing.
I planted some of my raff in garden burnt/clay soil mixed with sand. They seems to do well. I did put some dried leaves and peat on top the medium to mimic the habitat in the wild. The decayed dried leaves provide a damp cooling condition to attract a lot of ants to make their nets there, I know some of you may say the ants will provide food for the plant, but I just don't quite like it because whenever I "admire" my neps there are ants every where, luckily they are just the normal type of black ants that won't bite.
I'll try to plant them on ground one day to see the result. Robert, please keep us updated on the result on northiana.
I have the same result on growing amps in the same mix. The "apple tree" I had just posted not too long ago was planted in this mix too. I put some leftover Spiky Moss from my planted tank on the medium, unexpectedly they grew like wild and formed a layer of green carpet on top the medium.
I agreed with Robert that, as long as the growing media drains water well it will do OK for raff. A few of my raff in the same soil mix died after I found that they are water clogging in the pot. The key is make sure the soil is well drained.