Air layering is a very productive form of propagation to get a compact miniature tree with a decent trunk and a nice spread of roots.
Trees to layer:
- elms- really good
- Japanese maples- really good
- crabapples – good
- melaleuca- good
- conifers- not easy, take longer to develop roots, up to 6 months
- you can add air layers to trees in your garden, eg pomegranate
Best time to air layer is spring onwards when the sap is flowing, however, anytime as long as the tree is actively growing.
Things to consider:
- consider the new trunk direction to determine where to apply and how the new roots will form from the base of the trunk (it is not necessary to do a horizontal cut)
- choose the widest point of the new trunk
- choose an interesting trunk line and perhaps some branches to aid in the design of the new tree
- not worth it on skinny trunks
APPLYING THE AIR LAYER
Cut some sphagnum moss (about a cup full) and soak it in weak Seasol solution for about 30 minutes.
Consider girth, taper and direction of the new root base and use a pencil use a pencil to mark the tree at your chosen spot. This line becomes the new nebari. Then mark a parallel line below, using the diameter of the trunk for the distance between the two lines. If this is too small the tree will heal over the wound.
Use a a sharp pocket knife, cut along both lines and then , from top to bottom, strip off the top layer of bark. Then scrape off all the soft wood (cambium layer) until you get to the heartwood (the dead central wood of the tree).
Use a clear plastic sheet, approximately 30 x 30cm, to make a cup/ funnel, overlap the plastic and use and use string to tightly tie under the wound (about 5cm). You can cut a plastic lunch bag down one side. (Although black plastic is heat attracting and stimulates roots, you can’t see the roots growing through it.) It must be an airtight knot to stop drying or flooding. You can also use a cable tie.
To promote root growth, apply hormone gel (Clonex- red for hardwood) to the top edge of the cut where the roots will grow using a cotton bud or paintbrush. Do not apply to all the wound. Tip: Add a wire to the top cut (#2.0) to produce flair. Twist and cut short.
Squeeze the sphagnum moss until damp, not wet. Pack it liberally into the funnel to cover the top cut. Do not pack the sphagnum moss too tightly because the roots need space to grow if the moss is wet and airless the roots will rot.
Wrap the plastic around, overlapping it to make it airtight and tie the bag off, tightly at the top. Since it is airtight, the condensation remains in the bag and you don’t need to water.
Put a black skirt that can be lifted over it to generate heat but wait until you see plenty of roots.
Let the tree grow freely as this energy will stimulate root growth.
NOTE: You can also cut a plastic pot in half and cut he base to fit around the tree girth and tie together with wire. Add soil unto the wound, then add sphagnum moss around the wound and past the top cut and add another 2cm of soil. Water regularly as with your other plants. This works well for conifers.
CARE OF LAYER
Don’t trim the tree as the top feeds the air layer producing energy to stimulate root growth.
The aim is to develop roots all around the trunk. If using a pot, rotate the 180 degrees every three weeks. If layering a garden tree there may be less roots on the shaded side but these should develop within a year.
Remember that the tree may use the water in the bag or there could be evaporation so check for dryness. Up to 10 weeks should be fine. Note you should be able to see condensation in the bag.
REMOVAL
Wait until you can see vigorous root growth as these sustain the need tree.
Firstly trim the top branches. You can cut back quite hard so the new root system doesn’t have to struggle to sustain the tree. You may also consider cutting off the layer as it is easier to work with.
Open the bag, remove the string ties and gently unwrap/ remove the plastic.
Gently tease out the roots. Remove the moss, being very careful not to damage the new roots which will be tender and fragile. Don’t try to remove all the moss… it is OK to leave if the roots are tight. Lift the skirt of roots and use a saw to cut as close as possible to the underside of the new tree. Be extra careful. you can now flip the tree upside down and use branch concave cutters to trim the old trunk shorter. Leave 1cm in case of die back.
NEW TREE
Tease out the roots gently, trying to spread them horizontally, to form the new nebari and root ball. Place the air layer in a black plastic pot of soil. Don’t push down too hard as this will damage the roots. Add more soil above the roots and then sphagnum moss to retain moisture.
As you water, the soil will eventually filter down into the roots and they will strengthen. String tie the tree to the pot for stability for the first few months.
Trim the remaining branches to reduce stress and return to the bench in full sun. No special after care is required.
Note: If you air layer below the bottom branch the tree below may die. Air layer between branches.