Air layers are meant to force adventitious roots to grow so the part of the plant above the new roots can be separated from the mother plant, not to force shoots to grow. If one wants shoots to grow cut a notch in the vine/stem immediately above a node.
The growth regulator, auxin, is synthesized primarily in the apex (tip) of stems and branches. Two of its main functions are to suppress lateral breaks (side branching along the stem or branch) and to promote root formation or root branching. Auxin's flow in the plant is 'polar' meaning it only flows downward toward the roots. To force a branch to grow where we want it, stopping the flow of auxin is instrumental because it allows the 'dormant' buds at the node BELOW the notch to be activated. If we are truly air layering and trying to produce roots below a node, the notch needs to be below the node. It's purpose is to stop the downward flow of auxin and photosynthate (the plant's true food) so they accumulate in the tissues above the notch, which stimulates root formation. Air layers typically require the wound site to be surrounded by a grow medium to support root growth.
The trees below are hackberry and there is an air layer established on one of the trees. It is filled with gritty mix and gets watered regularly along with the trees in the tub.
Here, the air layer has been separated after 3 months and is growing on it's new root system.
There are several ways of preparing air layers for rooting. Cutting flaps in the periderm (skin or bark) or making a ring cut around the stem are the most common. Tourniquets are commonly used as well.
flaps:
ringed:
This Japanese maple was layered off of it's old root system via the tourniquet method. The roots you see are the new roots, the old root system has been sawed off. You can still see the tourniquet wire attached below the new roots.
Al
