Context: Growing orchids as epiphytes indoors
You can either attach them to a dead branch...or to a live branch. My vote is for a live branch. Some possible candidates...
Clearly they aren't all equally suitable to grow inside and be everybody's phorophyte. But that's what experimenting is all about. At the last show I went to a random lady said, "if you're not killing plants...then you're not stretching yourself as a gardener".
Which of these possible phorophytes will give you the most branch for your buck? One "shortcut" is that several of them can be grown from fairly large cuttings. Another technique for greater girth is...if your climate is suitable and you have the space (and patience), you can plant the phorophyte in the ground and then dig it up when the branch is thick enough.
Perhaps for a typical Phalaenopsis the branch should be at least as thick as your wrist.
In order for the Phal's roots to attach to the branch...the orchid has to be very firmly secured. I use a slip knot method to maintain tension in the 20lb fishing line.
If you do it right...you'll be able to water two plants at once...the Phal and its phorophyte. If the Phal is thirstier than its host, then you can attach it with some moss. You can also give the host a faster draining medium. Then the orchid's roots would extend into the phorophyte's medium. Quite often bonsai growers use orchid mix as their medium.
You can always raise the phorophyte's root crown above the soil line. This will help hedge against rot and provide a bit more surface area for the Phal. Plus, then you can see two sets of exposed roots...the Phal's and the phorophytes.
In terms of watering frequency...it depends on several factors...the temperature, the phorophyte, its medium...and the quantity and type of moss you gave the Phal. Personally, I'd water the Phal as soon as I attached it...and then wait and see how many days it takes for it to look wilty. The next time I watered the Phal it would be a day or two before it was likely to show any signs of drought stress. Generally though, a newly mounted orchid will require more frequent waterings than it will when it has numerous roots (straws) crawling all over the branch. So at least initially, you'd want the phorophyte's medium to drain especially well.
It might take some tweaking to get the drainage balance right...but attaching the Phal to a live branch will definitely increase the value to space ratio. You'll get more value for the same amount of space.
Check out these nice blank canvases...
Blank canvas 1
Blank canvas 2
Blank canvas 3