Hi Cat,
Yours are good questions. There's periodic discussion about mounting, but I don't recall any comprehensive thread on it.
In my experience, mounted orchids are great at freeing up shelf space (you can hang them, depending on the mounts) and are aesthetically much more interesting than pots. The downside is they need much higher humidity, because there's no pot to hold the moisture in. That won't work for many windowsill growers, unless you live in a very humid environment (I don't!)
Let's consider:
1. What plants to mount
2. What to use as a mount
3. What to place around the roots
4. How to attach the plant
5. How mounted culture differs
1. What plants to mount
Mounting works best for epiphytic plants (ie, those that typically grow in trees) that can take bursts of water, but then don't mind drying out some before their next watering. It's almost impossible to overwater a mounted orchid, but it's easy to underwater one. (Dends, Epis and Catts could be mounted, to name a few.)
Plants that enjoy more even moisture would do less well mounted. (Phals, Milts, Paphs, Phrags would not want to be mounted.)
2. What to use as a mount
Practically anything can be used. A rock. A hardwood branch. Driftwood. Common mounts include: tree fern slabs, cork bark, hardwood branches, and cactus skeleton.
The orchid's roots will grow into and around whatever it's mounted on, so be careful of acidity and salt concentration within the mount itself. Note that coconut husks and driftwood can contain high concentrations of sea salt. They should be leached thoroughly until their leaching water shows very low concentration of dissolved salts.
I tried my first mount on a slab of tree bark I got from the wood pile. That didn't work well, and I had to remount within six months, because the bark broke down over time as it absorbed all that water. Don't plan on "repotting" a mounted orchid - the roots may be too interwoven in the material. Choose something that will last for your mounts. Cork bark slabs are one of my favorites. And while I haven't worked with it, I love the look of cactus skeletons.
3. What to place around the roots
Most often, sphagnum moss is placed around the roots before mounting. Be sure to use real New Zealand sphag. It absorbs more water and retains moisture longer than other sphagnum mosses.
Moss isn't always used. Some plants are mounted without any moss. That would only be recommended for very humid growing conditions, however.
4. How to attach the plant
Monofilament fishing line is most often used to secure plants to their mounts, because it's strong and nearly invisible. However, if you've ever tried to work with it, you'll know how tricky small knots are to tie and secure. For the items I've mounted on cork bark, I use a skewer or tiny drill bit to make a small hole through the cork. Then I'll pass the line through and knot it to itself. I then pass it over my plant's roots (packed in a nice ball of damp moss) to secure them to the mount.
Others have suggested panty hose, strips from onion bags, and other loosely woven materials that are strong, nearly invisible when stretched, and will allow air and moisture to pass through freely. Some mount with glue guns. I've never tried it. While it cools quickly, the glue comes out very hot. I burn my fingers with it, so I can't imagine the plant would enjoy it.
5. How mounted culture differs
Humidity is the single biggest difference. Mounted plants don't enjoy the ambient humidity of a pot, so you have to supplement it in some way.
Watering, different from humidity, must be more frequent. There's little or no potting material to hold moisture near the roots, so water more frequently and for longer periods, giving the roots the opportunity to get a good drink.
Fertilizing should be weaker (so as to not burn the roots), but more frequent. Again, lacking potting media, the roots won't be able to draw any nutrients they would in a pot.
Julie
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