I decided to try setting up an airlayer on an in-ground black mission Saturday, using a 3-liter soda bottle packed with wet sphagnum and potting soil. I melted a hole in the bottom of the bottle with a soldering iron, and left the neck in place (I just split the bottle from top to bottom along one side, and for a few inches on the opposite side at the neck and bottom hole, just so I could open the bottle enough to fit it onto the branch). I then sealed everything with tape, covered it with a piece of aluminum foil, and topped it off with an old rag to keep the sun from cooking it. It’s not sealed air-tight, but it’s pretty close.
Unfortunately, I was working from memory and should have looked up this post before getting started. I "remembered" reading that girdling was more-or-less optional, so I left the bark intact, but now that I re-read everything it sounds like girdling is recommended on older wood (this is last year’s growth, more than an inch in diameter). Should I go back and girdle it? If so, should the bark be removed near the top, middle, or bottom of the bottle? I also notice that Jon cut the top off his bottle so he could add water. Should I cut a hole in the top for the same purpose (or just stick a drip emitter through the side), and if so, do I need a drainage hole in the bottom as well? Any direction would be appreciated–thanks.