An air layer can be taken from most trees in the UK once the first spring flush of growth has hardened off.  This is usually around mid May and you should notice the leaves will have lost their delicate feel and will have a stronger color.  At this time the leaf is in full ‘solar panel’ mode – it is converting energy back into the tree through photo synthesis.  All of these sugars are sent back to the roots to rebuild the energy store needed for future seasonal growth.

The air layer process relies on the ability of the tree to produce new root growth from the exposed cambium at the point we have removed the bark from the trunk / branch.  There is some ‘biology ‘ behind all of this so I will try to clarify exactly what is required to increase your chances of success.  Have a look through the next few images to help you understand why and what you are ‘removing’ when we ring bark the tree for the air layer.

As you can see, there are a number of different layers made up within the trunk or branch of a tree.  When we carry out an air layer we need to ensure we remove the following:

• Bark
• Phloem
• Cambium

The aim is to remove a sufficient band of material that ensures the tree will not be able to bridge the gap between the upper and lower cuts.  If we can do this then what should happen is the site of the upper cut will start to produce new root growth from the exposed cambium – in an attempt to repair the damage.  Normally I will remove an amount equivalent to the thickness of the branch…and a little bit more.

Once that cut is made then there is no means for the growth above the site to transport energy/sugar back to the roots – it can however still obtain water via the sapwood.  This means that if you do the air layer below the lowest branch you will have no means of keeping the roots alive.  Hence a ‘limited’ period exists to get sufficient new roots to maintain the existing growth above your cut site.  Clearly, if you are taking the air layer from a branch then their is no risk of compromising the health of the rest of the tree.  It is not unusual to take numerous air-layers off the same tree.  I have certainly done that with my cherry and maples.

There is a lot more detail on this subject; which includes the water transport system from the roots, but in essence, it is important to recognise why certain things are done and why there are time constraints. The aim is to take the air layer off in early autumn to give enough time for young roots to establish and harden before the winter.

I have selected a point above the ugly swelling and then cut away at an angle to try and establish a wider base for roots to propogate from.  It is vital that this upper cut is done with a sharp knife and ‘cleanly’.  You are trying to avoid any ripping or tearing to maximise the ability of this exposed cambium to produce new roots.  You can dust the cut and above it with rooting hormone to assist some trees with this process.

I use pre soaked sphagnum moss as the growing medium that I pack around the cut site.  You can use plastic as a wrap around the moss but I have had more success using an old plastic nursery pot with the centre cut out.  I ensure that the top of the cut sits in the centre of the pot – this should be the best place for balance of water and oxygen.  I use wire to secure the pot at top and bottom which allows an easy method to check for root growth later in the year.  I pack the pot full of moss and then soil and water it.  The rest is up to nature…

I will keep the soil moist and the tree in a shaded wind free spot until I am ready to separate the air layer.  I am aiming for mid August so I will loosen off the wire and check progress sometime in late July.

If the layer has taken then I will cut the trunk beneath the container and try to ‘slip pot’ the seperated tree into a larger plant pot – without disturbing the root mass.

I have included an image of the maple (above left) showing the original lower half of the tree.  Hopefully you can see the shape that the shorter bonsai will take once the air layer is removed.  If things don’t go well then at least I will still have a better bonsai to work with next year…