Have you considered air layering?
If, like me, you have more years behind you than in front then the question of new material can be a tricky one. On the one hand you are probably not prepared to grow from seed due to the years involved (unless you want a very small tree, which is fine, if that is what you want) but on the other hand do you have a substantial pot of money to dedicate to buying mature trees?
I have one word for you……… ‘Air layer!’
Ok, I know it’s two, but who’s counting? and it is a great way to increase your collection.
So, “what is an air layer?” I hear you ask.
An air layer is:-
‘A method of propagating a plant by girdling or cutting away part of the stem or branch, packing the area with a moist medium such as sphagnum moss to stimulate root formation so that the stem or branch can be removed from the parent and grown as an independent plant’.
This is an excellent way of creating material virtually for free, just the cost of some sphagnum moss and a little time.
The other items needed most people will have lying around indoors or in their garage or shed. (Clear and black plastic bags/sheeting, cable ties or garden/bonsai wire).
I have performed a number of air layers over the last few years, some successful and some not so! Some species are easy and some are nigh on impossible! I will leave you to experiment for yourselves as that is half the fun, right?
Anyway, the subject chosen for this blog is a Japanese Maple or Acer Palmatum which as it happens is one of the most obliging of species when propagating in this fashion.
The first thing to consider when attempting an air layer is, ‘Is it a worthy piece of material?’
There is little to be gained in air layering a branch if it doesn’t have any redeeming features like decent taper or generous thickness etc. Air layering on most deciduous trees is generally straight forward and after 2 or 3 years to recover and gain strength in their new roots you can, if you so choose, cut all the branches off and regrow them. This is not an option with say a Juniper or Pine. If you cut all the green off either of these you can wave goodbye to them!
So back to my original statement.
It has to be a worth while piece of material.
The tree that was going to be the donor for this air layer was getting too tall for its current location in the garden. So rather than just pruning off the bit I didn’t want, I chose to air layer the entire top of the tree. This will a) allow me to regrow and train the top of the tree as I see fit and b) give me a new piece of material to train as a bonsai.
The current top of the tree splits into 4 main branches and one very small side branch low down on one of the other branches (fig.1). I decided to apply the air layer just below where the 4 main branches emerged from. My aim is to have the piece of material eventually trained into a multi trunk or clump style.
When attempting an air layer the time for starting is, like most things in bonsai, always debatable as to when is best. Some claim it is best to start before leaves are fully emerged and others say wait until the leaves have been out for a number of weeks and the cuticle has formed. I have only ever attempted them on deciduous trees after the leaves have emerged and been out for a few weeks. I have done them on Junipers in the past and I chose to apply them at the same time as the deciduous trees to keep things simple. You can make you own choice.
We had had a mild winter coupled with a very early spring due to warm temperatures from mid February. As a consequence all the trees in the garden were full of leaves by mid April. So by late April I had decided to make a start on the piece I wanted to air layer.
The first thing to do is get all the items you will need ready as the last thing you want to be doing is looking for items halfway through.
You will need the following:-
Sturdy clear plastic bag or sheeting
Black plastic bag or sheeting
Silver foil (optional)
Cable/zip ties or bonsai/garden wire
Sharp clean hobby/Stanley knife
Moist Sphagnum moss and rooting hormone
Alternatively, you can use specialised air layering balls or a plastic flower pot (this will need to be cut in half to allow it to encircle the trunk) instead of the clear plastic sheeting.
Ok! Got everything? Then we’re ready to go!
I started the process by removing any small branches that would be in the way of applying the air layer. After this, I used the hobby/Stanley knife to mark around the trunk circumference at the top and bottom of the area to be worked (fig.2).
The length of the air layer needs to be twice the width of the trunk diameter. If you don’t have enough of a gap or fail to remove all the bark/cambium the air layer is doomed to fail before you start. The tree will simply create callous tissue which could bridge the gap and just allow the tree to carry on as if nothing had happened.
The next step is to carefully remove all the bark within the top and bottom marks and completely girdle the trunk leaving the cambium layer exposed. This is the pale
yellow/green layer immediately under the bark which can be seen in fig.2 above. Following on from this, all the cambium layer must be removed. This is easily accomplished by scraping it off using the hobby/Stanley knife holding the blade at ninety degrees to the trunk and scraping it up and down within the exposed area. Try not to create any damage to the top line as this is where the new roots will emerge from and a clean cut will give the best chance of a good set of radial roots growing all around. You can see when the cambium has been removed as the layer underneath has a yellow/white colouration to it. The differences are subtle so make sure you are confident all the cambium is removed (fig.3).
Next, make up a paste of rooting hormone powder and apply it to the top cut making sure it is applied well all around the edge.
Then we need to apply the sphagnum moss around the entire area. There are two methods you can use to do this. The first is to cut a piece of sturdy clear plastic big enough to encircle the area with plenty of room to spare top and bottom. Wrap it around the trunk, with the join towards the top and secure it at the bottom with a cable/zip tie or piece of bonsai/garden wire. Do not attach it too tight or it will stop the flow of nutrients up from the roots. Next, begin filling the ‘bag’ with the moist sphagnum moss taking care not to knock off all the hormone paste around the top cut. Once the ‘bag’ is full you can apply wire or
a cable/zip tie around the top. Aim to have the air layer section in the middle of the sphagnum moss ‘bag’. The ‘bag’ must be completely filled with the moss which in turn must be in contact with the trunk of the tree. Again do not tighten the wire or cable/zip tie too tight or you will stop the flow of nutrients from the top of the tree. Once this is completed wrap the entire area in a piece of black plastic to ensure no light can enter. This is the ‘bag’ method.
The method I used is essentially the same but I have the air layering balls that were a gift so I am using them (fig.4).
Make sure the hole in the two half’s of the ball line up and are
not too tight around the trunk. I have had to enlarge mine a little to accommodate the four branches at the top. Fill each side of the ball with moist sphagnum moss and place around the trunk with the air layer area in the middle of the ball (fig.5). Secure the two halves with some sticky tape.
I then chose to wrap mine in silver foil to exclude the light and reflect some of the heat from the sun (fig.6). A piece of black bag as a covering will generate a lot more heat within the air layer than silver foil. As I have a south facing garden the last thing I wanted was to have it getting too hot and drying out.
The air layer is applied.
All that remains is to monitor it to ensure the moss doesn’t dry out. If you use the ‘bag’ method you can leave the top slightly loose to allow water to enter when it rains, or by watering can, if it has been too dry. But don’t forget to stab a few drainage holes in the bottom. The ball already has a small hole in the side to allow the addition of water when needed and I have found a big syringe is the perfect partner to do this.
A number of factors will determine how quickly roots will form some may be ready in 6-8 weeks and others may take 3-4 months or even longer. The best way is to keep your eye out for root formation whilst you monitor moisture levels. It will be very obvious when roots are starting to form as you will see them appearing in the moss. They look like white worms winding their way around!
Once the tree has made good progress in filling the bag/ball with roots it’s time to remove it. It can then be potted on to allow it to continue to grow and develop it’s own roots further.
The amount of roots shown in the picture is the minimum amount you should be looking for (fig.7). Some people may say there is insufficient roots. I was happy with this amount as I had intended to remove quite a lot of top growth after severing the branch. If you don’t intend to remove any top growth it would be prudent to wait for a few more roots to form or even fill the bag/ball completely.
Depending on how thick the branch that has been air layered is, will determine how you must remove it. Mine was of a thickness that I could remove it using sturdy garden loppers. You may need to use a saw. If you do need to remove it using a saw, then be careful not to damage the new root ball as it is very delicate at this stage. A battery operated reciprocating saw is a perfect partner for this process. If you don’t own one of these get a friend or family member to hold above and below the air layer to minimise the risk of damage.
Once you have removed the air layer from the parent tree you will need to pot it up in it’s own pot. The ideal pot for this is a pond basket. It has hundreds of tiny holes all around the sides which allow for an excellent exchange of air and free draining of moisture which is the perfect environment for our new root ball.
Exercise care when removing the clear plastic or air layering ball as the new roots are extremely delicate and will snap very easily.
Attach some guy wires to the sides of the pond basket and place a layer of your preferred bonsai substrate (free draining but moisture retentive and certainly not potting compost!) in the bottom of the pot. Then stand your air layer in the pot and fill all around with more substrate whilst holding the tree in place. Do not be tempted to poke substrate around the roots like you would usually do at re-potting. You will be guaranteed to damage the new roots! Once you have filled up the pond basket (ensuring all the new root ball is covered) you can attach the guy wires in the best manor to prevent the tree rocking in the pot (fig.8).
Give the pot a thorough watering until the water runs clear. This ensures any dust is removed. Then place in a bright but shaded part of the garden away from direct sunlight. Keep your eye on the moisture in the pot. Depending on ambient temperatures you may need to water more than once a day!
The last picture to show here is that after just two short weeks in a pond basket the air layer has already started pushing new roots out the bottom of the pot (fig.9).
This really does show what a perfect training pot pond baskets are.
I hope this blog is useful and that it gives you some inspiration to ‘have a go’ at air layering. It really is a very useful tool in the bonsai hobbyists armoury.