I would agree with much here, but want to point out that, in my tank, volunteer ferns do show up on occasion. Got a
Pteris cretica with over a dozen fronds growing on a moss-covered lava rock--I honestly have no idea how it got there (I wonder if the spores come in on or in plants from Black Jungle--have heard that greenhouses often get lots of volunteer ferns, pileas, etc....)
Now, my tank is way warmer than your PDF tanks; can get to high 80s in summer. Yet this fern, with constant moisture (not wetness) and 75-80% humidity, does fine.
Fern facts I have learned:
--Most do not like wet substrates. Moist, not wet, with good drainage. Marsilea and Water Sprite are exceptions. (Of course, Java fern and some Bolbitis not only want a wet substrate but super-high humidity.)
--Most do not tolerate being moved. Meaning, it is not easy to get a "big" plant (4" pot from the nursery) and just stick in your substrate--they will shock and/or rot. Much better to start with small specimens and place them on top of the substrate with just a bit of NZ sphag to hold them in place, or in a crevice with most excellent drainage.
--Not all are suited to terrarium life. MantellaPrince is right on about Davallia and Humata, ET fern and Caterpillar fern all grow well
on top of the substrate; Pteris grow well on rocks; Microgramma can grow in moist tanks on the back wall. As for Birdsnest and Staghorns, these can be mounted only in huge tanks (These grow slowly but will get big. And to repeat, four years from now they will not take kindly to being torn off their mooring.) So no, I will never move the Pteris--and expect it to live. As for Hemionitis, I hear good things but have never tried it.
--Definitely lower the temps until the plants are established. Once established, many ferns and other "intermediate" tropicals will tolerate warm days as long as there is a real (5-10d) temperature reduction at night.
--Oh yeah: good drainage
