What is air layering?
Air layering is a relatively fast and easy method of propagation you can use to create bonsai from larger trees and shrubs. In essence, air layering is way to grow roots on a part of the plant that otherwise wouldn't grow roots, like a branch or in the middle of the trunk. This technique is usually carried out in mid to late spring.
This method of propagation creates an identical copy of the 'parent' plant, much like when you take cuttings. It's particularly interesting if the parent plant has good characteristics, because these will be passed down to the new plant. This can be small foliage, short internodes, beautiful fall or spring colours, etc.
In nature, air layering can occur when a low hanging branch of a plant gets covered by soil. Some plants will take root and the new plant can then sustain itself.
Choosing the right spot
Here you can see an example of an air layer I did recently. The basic idea is to cut away a piece of bark and wrap it with spaghnum moss in order to promote root growth just above the place where you removed the strip of bark.
Here I'm trying to create a bonsai out of a Japanese maple, or Acer palmatum. This is a special variety called 'shishigashira'. It has curly foliage, bright green spring colours, deep red and orange fall colours.
It's very slow growing, but it produces beautiful bonsai if you're patient enough!
The first step in air layering is to determine which part of the parent plant you want to grow as a bonsai. Choose a part that has a nice characteristics for bonsai. In my case, I chose a straight branch, because I want to create a broom style bonsai.
Usually you could look for the following features:
- The branch you're going to layer will be the trunk of the new bonsai tree. Unless you're going for a broom style bonsai like I am, choose a branch with a lot of movement.
- The trunk line of the new tree should be broader at the base - where the roots will grow - and thinner towards the apex.
- Good branch placement
- The first branch of the new tree should be at aprox. 1/3 of the height of the new tree. Choose the area where you want roots accordingly!
2 to 3 year old branches will generally root easier than older (and bigger) branches, but this varies from species to species. For example, elms can be air layered off of branches (or trunks for that matter) that are 20 cm in diameter. On the other hand there are species that don't grow roots that easily and often end in failure. There are countless of sources on the internet where you can find information on propagation of different species. I recommend you do some research on the specific species you want to air layer before starting the process!
Air layering doesn't really require special tools or fancy equipment, but you will need the following:
- a very sharp knife
- isopropyl alcohol (optional)
- rooting hormone (optional)
- spaghnum moss
- plastic bag or cling wrap
Once you have decided where you want to make the air layer, you're ready to go!
How to air layer
First, remove any unnecessary branches from the spot where you want roots to grow. Then remove a ring of bark, all the way around the branch. It should look something like the branch pictured here. Make sure that the strip of bark that you cut away, is at least two times the width of the branch.
Roots will grow best at an internode. In older branches on maples, you can vaguely see a ring, sometimes with a couple of buds. This is an internode, from which new growth usually develops easily.
Make the cut just below this ring.
It's important to know that new roots will form above the cut.
After you've pealed away the bark, you can see a layer of green tissue. This is called the 'cambium' and it's responsible for new tissue growth. If it's exposed to air and light, it will create callous tissue or scars. If you leave this green layer in place, the plant will try to heal over the wound with callous. If this happens, new root won't form and the layer will fail. It's important scrape away the cambium layer before proceeding with the next step.
When you've scraped away all the green tissue from the cut site, you should only see white tissue. In order to make sure most of the cambium cells are gone, you can rub isopropyl alcohol on the cut site.
Air layering can be hit or miss sometimes. To improve your chances of success, you can add rooting hormones just above the cut. They usually come in the form of a gel or a powder. Either is fine, just make sure you apply it all the way around the branch.
Next you want to take a small plastic bag, or some cling film, and moist spaghnum moss. Note that the moss should be moist, but not dripping wet. So first submerge it in water and then squeeze out the excess.
Wrap the moss around the cut site and the area above it. Then wrap the plastic around the moss to hold it in place. Secure the plastic with aluminum wire at the bottom and up top, and make sure the moss is pressed firmly against the branch.
Two things to keep in mind:
- Make sure the moss not only covers the part of the branch where the bark was removed, but also about 5 cm of the branch above the cut point. Roots will emerge right above the cut!
- To improve the chances of success, the moss should be pressed tightly against the bark, but not so tight that roots won't be able to grow through the moss.
What kind of plastic you use, really doesn't matter that much. The purpose of the plastic is to hold the moist spaghnum moss in place, and prevent it from drying out. I've even used plastic containers with some success, although the moss tends to dry out quicker in open pots.
You can buy spaghnum moss online. I use the dried kind that is used in terrariums. Obviously, you'll have to rehydrate it before use.
You're basically done! The only thing you have to do now, is wait and make sure the moss doesn't dry out too much. I usually check it once every couple of days. If I notice a change in colour (from dark to light), I know the moss is getting dryer. I then open the plastic a little bit and add some water.
After 6 to 8 weeks, new roots should appear. Some species can take up a full growing season, or even a full year to sprout new roots. If you think something went wrong, open the bag and check if there is scar tissue. You can simply remove this, reattach the moss and plastic and start over.
Near the end of the growing season, the plastic bag should be full of roots. You can then cut the new plant from the donor and start nurturing it as a seperate, new plant. With vigorous plant, you can sometimes seperate it during the summer months.
In a couple of weeks, I'll do a follow-up of one my air layers and show you how you can safely remove it.
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