Known for centuries in China, air layering allows the branch being cloned to be supported by the existing root system of the mother plant. The leaves and stems continue to grow, receiving water and nutrients from the roots, and new roots are formed at the same time.
To air-layer a clone:
The branch to be cloned should be at least 1/8" thick. If the branch is too thin, it may not be able to hold itself up after doing this procedure.
Pick an area directly below or around a node, same as if you were to clone normally. Remove the outer layer of tissue, the phloem, by either scraping it off or cutting it as follows:
Make two cuts around the stem, just deep enough to cut through the outer layer. Cut too deeply and you will damage the inner xylem, disrupting water/nutrient flow to the leaves and possibly killing the branch. A sterilized scalpel or razor blade is used to make clean cuts. Connect the two cuts with a single vertical cut at the same depth. If done correctly, the phloem (bark) should simply peel off.
The phloem can also simply be scraped off, but this method is more apt to cause damage to the xylem unless you know exactly how deeply to scrape.
The inner xylem brings water and nutrients from the roots to the leaves. The outer phloem normally carries carbohydrates from the leaves to the roots. Between these layers is another thin layer called the cambium. It is from this layer that the new roots will grow. The wound site is covered in rooting hormone, and is wrapped in your choice of growing medium.
In this case, rockwool cubes are used. Soil can also be used; simply wrap some plastic wrap around the wound site, making a round "pocket." Soil is packed into this pocket and taped closed. Small holes or slits are cut to allow the soil to be watered, and to allow airflow. If using rockwool, soak in 5.5 pH water prior to use. Cut the cube in half and just put the two halves together around the wound site. Secure with twist ties, string, etc.
The biggest challenge to using this technique is keeping the medium moist. If it dries out, the sensitive tissues will die and you'll just end up with a dying/dead branch on your plant. After a couple of weeks, some roots should be growing from the wound site and the branch can be cut below the medium and transplanted.
Edited by zpyro, 17 April 2009 - 06:45 PM.