A home gardener can propagate a new cherry tree using the branch from an old tree. This process is called air layering and involves wounding a branch, then sprouting roots from the wound while it is still attached to the parent tree. The branch can then be severed and will grow independently. It will be an exact genetic copy of the variety of cherry tree the branch came from and will produce the same type of fruit. This is a cheap and simple way to increase the number of trees producing your favourite type of cherries.
Select the branch you want to use to grow a new cherry tree. It should be about half an inch in diameter 12 to 18 inches down from the growing tip.
Cut a ring of bark from the branch about 12 to 18 inches from the tip in a space between nodes. The ring should be about twice as wide as the branch is in diameter. Start with two parallel scores around the branch at the desired width, then peel away the bark from inside the ring. Make sure to cut all the way around the branch so no bark is left connecting the main part of the branch to the tip. Use a sharp clean knife for this. New razor blades work well and are disposable.
Scrape away the thin sappy layer within the ring with the edge of the blade. This is the layer that transports nutrients and water around the cherry tree. It lies just under the bark on top of the hardwood.
Dust rooting compound onto the wound with a small paintbrush. Rooting compounds contain root growth hormones and usually some kind of anti-fungal agent. They are available in most garden centres in powder form. Liquid form will also work, but it is harder to apply.
Wrap a handful or two of damp sphagnum moss around the wound. Make sure it is in full contact with the branch. The wound needs to be completely covered with about an inch-thick layer of moss on all sides. Thicker branches may need a little more moss.
Wrap the damp ball of moss with clear plastic. Any type of clear plastic will work. Cling wrap for food storage, bubble wrap or even a grocery bag cut in half will be fine as long as you can see through it.
Tie off the top and bottom of the plastic-wrapped moss ball with twist ties just above and just below the wound. This holds the moss firmly against the branch and keeps the moisture inside.
Wrap the plastic in aluminium foil to block the sun. Direct sun can overheat the moss ball.
Check the moss ball after a week or two to see if roots are forming inside the plastic bag. Be sure to replace the foil if it needs more time. The branch is ready to cut from the parent when the roots have reached the plastic and are starting to curl around in the moss.
Cut the branch right below the wound with pruning shears.
Remove the plastic and moss from the severed branch. The wound should have a mass of roots growing from it. Now the new cherry tree can be potted in a small container of commercial potting mix. It needs to be placed in a shady, protected area for a season or two to grow out before it can be planted into the landscape. Keep the soil slightly moist but not wet.
The best time to air layer cherries trees is in early summer to midsummer when the new growth from spring is becoming established. This also gives the new tree the rest of the growing season to develop roots. Poke a hole in the top of the bag to add water to the moss if needed and a hole in the bottom so excess water will drain out. The moss should remain slightly damp and not be allowed to dry out.
The new tree may not have the same types of roots as the old tree. The upper part of many cherry trees is grafted to the roots of a different variety of cherry right at the ground level when young. The top produces the desired variety of fruit and the root stock is adapted to local soil types and climate conditions. This means that the new tree created by air layering will have the same types of roots as the upper part of the tree normally would have, had it not been grafted. This may make the new tree less adaptable or less vigorous, but not necessarily unsuccessful, compared to the old tree. If the roots are not very well developed when the branch is severed from the cherry tree, place a clear plastic bag over the entire grow-out pot and newly planted tree, making a mini-greenhouse to hold in humidity. After a week or two, acclimate it to the atmosphere by poking larger and larger holes in the bag every day for several days in a row until you remove the bag entirely.