What's a good "soil" for terrestrials?
 

I'm planning to order a Pecteilis susannae this week but I don't really know what kind of potting mix to use, just in case the vendor sends the plants bare-root.

Does anybody know any good potting mixes? Preferrable ones that don't have too many different components.
I'm thinking 4:2:1 Garden soil, bark, stones. Would this work?

Why stones?

I find sphagnum is a great medium for terrestrials.

>Why stones?
I figured it would aerate the soil I a bit and would look somewhat nice.

Can I mix sphagnum with garden soil?
Maybe I can do 3:2:1 Soil, Sphag, bark

I've had success with potting soil (40%), fine bark (25%), moss (10%) and perlite (25%). I don't know what you have available locally but you could probably amend garden soil with leaf mold.

I don't have perlite available near me.
Not sure about leaf mold, though I probably have some near me.
What about garden soil+sphagnum+bark+decomposing leaves? All I have to buy is the sphagnum then.
Side note: There's also some weird sheet moss available around. Will that work? I could take a pic of the sheet moss.

You should ask the seller as well if he's local. I don't know if your sheet moss is 'natural' . Ours' seems dyed and is used for decorative purposes.

For Cymbidiums & Calanthes, I use:

3 parts chunky peat (1/4" to 1" [= 0.4-2.5 cm) nuggets)
2 parts composted manure (I buy at Home Depot in garden center section)
1 part bark
1 part perlite

If you don't have perlite, use Wikapedia offers some possible substitutes at the end of the article. Perlite is usually used to help keep the soil from compacting. I often use sand along with perlite for my potting mixes.

Here is the link:

Perlite - Wikipedia

How about pumice as a substitute for perlite? It is heavier, which can be a good thing to keep the pot from falling/blowing over and has similar air-trapping qualities.

Look up where it grows, in what type of soil and in what ecologic niche. Different "terrestrials" grow in leaf litter, humus pockets on cliffs, sand, thin mossy layers on rocks, bogs,....

I found just one habitat shot. It looks like it grows in real soil, not loose mixes. Can you read this page?
scienceblog: Anggrek Susannae (Pecteilis susannae (L.) Raf.)