You can air-layer the top off of a small plant, or a branch off of a larger tree.
You will need a few basic supplies. This was done using a 1.5 liter water bottle, a clothes pin, duct tape, a grafting kife or other sharp knife, rooting media (I used 100% compost), and water.
Cut the top off of the water bottle, cut some drain holes in the bottom, slit the bottle from top to bottom, and make a hole large enough to go around the branch to be air-layered.
Well, I finally got smart. I was cutting the top of the bottle, splitting the side, and cutting a hole to fit around the branch in the bottom. But the bottom of the water bottles was very hard and tough to cut towards the center. So, I finally realized that I could saw off the neck of the bottle, which left a hole of the right size, and then cut the bottom off where the plastic was thinner. Voila! Faster, easier.
Girdle the branch as follows. Make two cuts about 1" apart all the way around the branch. Girdling helps to initiate rooting at the desired location because it interrupts the flow of nutrients from the leaves to the roots.
Poor pix, but you can see the latex sap dripping from the cuts.
Peel off the bark between the two cuts.
Bark completely removed.
I used the clothes pin to hold the bottle at the right place on the branch. It has enough tension in the spring to stay tight, and rests nicely on the bark at the bottom of the cut.
Wrap the bottle around the branch and let it rest on the clothes pin.
Tape the bottle together. Fill it with rooting media and water it well. You may need to add water from time to time. I added a little water every few days.
If in a sunny place, cover the bottle with aluminum foil to reduce heating of the rooting media.
After the branch is well rooted, cut it off below the bottle.
Close up of root area.
You should have an abundance of roots. This branch is used to getting water flowing up from a large rootball, and will now be surviving on a smaller rootball until it has time to develop additional roots.
View from the bottom where the branch was cut from the tree.
View of the roots, after carefully removing the bottle. The roots are tender and fragile, so use extreme care when removing the bottle.
Pot up the branch, and place it in shade and high humidity for a couple weeks till the root mass increases and the plant is stabilzed with the roots and leaves are in balance. In this example, the roots were starting to grow out of the drain holes of a 5 gallon pot in about 5-6 weeks.
Air layering can be used on many other plants, as well. Figs naturally root easily. Others are more difficult and take much longer. That makes water control in the rooting media more critical. There are many other ways to air-layer which can be easily found on the internet.
The original plant will reflush with new growth, often while the air-layer is rooting. This is also a way to "prune" a tree shorter and produce an extra plant in the process.