What sort of plants do you grow in your jars? The only plant I’ve ever been able to grow successfully without plant specific substrate and a strong plant light is anubias.
Um, it's been a few years now. Let me go look it up...
Yup, Anubias nana petite.
Also java fern (a miniature variety), Saggitaria subulata ("Dwarf sag"), Echinodorus compacta ("Rosette Sword"), and some kind of moss.
Most of them had inert gravel with a few dead leaves under it. A few of the not-rooting kinds might have been in plain water.
They all ended up with a few dead bugs floating in the top over time, which may have helped with fertility
There may have been one or two other kinds of plants that died, but it's been 3.5 years and I'm pretty sure I still have all of the ones on that list, plus a few more I've bought after setting up the actual tank. I've been quite pleased with the rosette sword: it looks happy, has stayed about 6" high, and has made at least 2-3 babies. My tank is only 12" high so short height was important to me, I avoid stem plants because I don't like having to prune regularly, and I wanted something with a large root system to use nutrients from all parts of the gravel. So it's been perfect. The more common sword plants would have been my first choice if height were not an issue.
When I set up the actual tank I used the same kind of inert gravel, and whatever mulm/algae/dead plant leaves had accumulated in the jars. More has accumulated since, so it's almost like a kind of soil by now, probably complete with underwater earthworms (I added "Dero worms" for that purpose, but I haven't gone digging to see if they are still there. Years ago in another tank, I had "California Blackworms" living happily in the gravel, but this time I wanted to try a smaller kind.)
Light:
The jars with plants were under a pair of fluorescent tube lights that we were using with other houseplants. Probably cool white, but I no longer remember for sure.
For the tank, I use spiral fluorescent bulbs, color temperature 5000k or higher, I think actually 23 watts (the big text on the package claims they're equal to 100-watt incandescent.) I put them in either clamp desk lamps or (my current favorite) in those metal reflectors meant for heat lamps, which I can sit on the screen cover of the tank. Screen cover provides good airflow while keeping out kids, toys, pets, etc.