If you haven’t done so yet, please read part one of this article at the above link.
Now that you have a basic understanding of what a layer is and why it works the way it does, let’s get to actually producing one.
creating an air layer on a maple with a terrible base
To create our air layer we need to prepare a few things first.
You’ll need a sharp knife to score and peel the bark. I like to use a retractable heavy duty utility knife, similar to what you would use to cut boxes or carpet. It is razor sharp so scores and carves wood quite nicely, is durable, and retracts easily for portability.
Thick clear plastic of some sort. I prefer not to use plastic cling or saran wrap as it is somewhat thin and not that durable. A good alternative is a zip-loc freezer bag, preferably gallon size. The bag can be separated at the side and bottom to create a perfect size, durable sheet to wrap your tree or branch with. It’s clear as well which provides for easy observation of any new root formation without having to remove the plastic.
Wire or string to wrap the plastic. A rubber band works nicely and creates a tight seal as long as you have an easy way to move the band over the layer. If not, wire would be my second choice. Using a thin wire and twisting it at both ends of your layer will enable you to quickly remove it when adding water to keep the layer from drying out and then re-twisting to close. If the layer is created and sealed correctly, water should not have to be added, but during hot, summer months sometimes this is unavoidable.
Sphagnum moss. This type of moss is easily purchased at any garden supply store and sold dried in bags. The moss should be soaked in water for several hours before use to make sure there is plenty of moisture available for your layer. Remember that when wet, the moss will become quite compact so you should make sure to prepare more than you think you will need.
Rooting hormone. This is optional, and if you don’t already have it available, it is perfectly fine to continue without it. When cutting into the bark, the rooting hormone is brushed at the cut in order to come into contact with the cambium that has been exposed. If you remember from part one, the cambium is responsible for producing adventitious roots, and exposing it to the rooting hormone only serves to speed up the process. The air layer, if properly created, will still succeed without the rooting hormone.
That’s all you need. Our first example specimen we will produce an air layer from is Liquidambar styraciflua, more commonly known as sweetgum.
beautiful sweetgums in autumn
The humble sweetgum is one of the most common trees in North America. It is a vigorously growing species that can reach heights of 80 to 120 feet (24 to 36 m) and displays beautiful red, orange, and yellow foliage during the fall. Although producing rather large maple-like leaves and long internodes when left to their own devices, with proper pruning and training both can be reduced resulting in a beautiful bonsai that gives a truly stunning multicolored autumn display every year. If considering the sweetgum for bonsai, keep in mind it is strongly apically dominant, which means the top will have to be judicially pruned in order to keep the lower branches from weakening and dieing off.
When picking a good candidate for an air layer from a branch in the field, I look for a few different things. The first and most important thing you will need to succeed is a good amount of foliage at what will eventually be the apex, or top of your tree. Remember from part one I pointed out that the energy and sugars created by the leaves during photosynthesis will be what drives the new root growth of your air layer. Without this foliage, there will be nothing to produce your roots. So it follows that the best time to create a layer for a deciduous tree will be when growth is strongest and foliage is most plentiful, usually during the early to mid summer.
our chosen branch with strong foliage growth
Besides foliage, keep in mind the style of tree you would like to cultivate. Formal and informal upright, cascade, etc. These styles will determine the type of branch to layer from the host tree. In the case of this particular sweetgum, I would like to choose a branch with slight movement that will ultimately result in an informal upright.
Taper, or a gradual decrease in diameter from base to apex, is important to consider as well. Although in most cases, the exterior end of the branch will be chopped once separated from the tree, the better taper you have to start with, the more natural the tree will appear once potted.
the smaller branch on the left will ultimately be the apex of the tree
And lastly, a currently growing leader branch will speed things along when it comes to taper. If you can select your limb so that a smaller branch is currently growing at what will be the apex of your final tree, then chopping back to this branch once properly rooted will give a much greater impression of tapering growth.
the bark is scored deep enough to pass through the cambium and phloem
Once a branch is chosen, use your knife to score the bark completely encircling the branch so that you will have a some idea of where the bark should be removed. Remember to make the score deep enough to pass through not only the outer bark, but phloem and cambium as well. If you recall from part one, this must be done to ensure that what the foliage produces is not returned to the main tree, but instead is focused on growing your new root structure. It is recommended to remove a section of the bark at least 1.5 to 2 times the diameter of your branch. This will give you enough distance so that the bark is unable to bridge the gap and repair itself. If it does this, your air layer will fail.
notice the reddish phloem that has been removed as well as outer bark
Next, use your knife to remove the outer bark from around the branch, as well as the slightly softer phloem until you start to approach the xylem or sapwood of the tree. Be careful not to damage the xylem too much, as this will be transporting water to your layer from the tree. You will know when you have come to the xylem as this wood is much harder and has a slightly glossy appearance.
rooting hormone powder applied
If you are using rooting hormone, dampen the cut you’ve made and apply it liberally to the bark, especially making sure to cover the area at the cut where the cambium has been exposed. The vascular cambium will usually be a lighter green in color. The phloem thickness can differ greatly depending on the species of tree.
tie the plastic securely at one end
fill the bag with the sphagnum moss
Next securely tie off one end of your bag or plastic sheeting above your cut and begin to fill it with the damp sphagnum moss. Pack as much moss as you can into the plastic as this will be your growing medium for the next few months. In this layer I started to run out of moss as I was somewhat under prepared and didn’t bring enough. What I have should be sufficient though as long as I don’t allow it to dry out.
secure the other end of the plastic to finish the job
Tie off the other end after you finish filling the plastic. Make sure both ends of the plastic are tight up against the wood as you need to preserve as much moisture as possible. After everything is secure you are done. Check the bag periodically to make sure the moss is still damp. The good thing about using a clear plastic instead of other materials is that it’s easy to monitor not only when roots have started to form, but moisture levels as well. If the moss starts to lighten color or you begin to see condensation lessen against the walls of the plastic, unwind the wire on one end and dampen the moss.
In Part 3 of this series, I’d like to show you a few more examples as well as some other things to look for and some to avoid when creating an air layer.