By Gardener Jack Many shrubs and small plants can be propagated by cuttings but others, particularly trees, are resistant to rooting in the ground. The answer in many cases is to use an old technique that originated in India called gootee and employ modern materials to help us. Gootee used a special clay soil to surround a wounded limb and bound it with coconut coir matting. A length of rope or cloth led from a water reservoir - usually a section of bamboo cane that was hung in the tree - and was wrapped around the coconut coir matting to keep it moist. Today we can use plastic wrap, aluminum foil, and sphagnum moss to make an air layer. These make the process far easier. The principal of air layering is quite simple. If a limb becomes traumatised it will attempt to put out roots. All plants take in water, and the nutrients contained in water, through their roots and distribute it throughout the plant from the top. This is why the top growth of a plant is the first to show stress in a drought situation. The moisture is carried to all parts of the plant through several thin layers of tissue that lie below the bark. When you scratch a tree with your thumbnail you will reveal the green layer of tissue. Scratch harder and you will instantly come to the core of the tree. This layer that provides nutrients to the tree is very thin, only a fraction of an inch thick, and reminds us that even a mighty tree is strangely vulnerable. Were we to remove the bark and tissue just below a growth node on a tree limb we would prevent moisture and nutrients from travelling any further. The area around the growth node will swell somewhat and if a moist growing medium is placed around it, roots will develop in time. In practical terms, the most important aspect of making an air layer is ensuring the limb is truly isolated and no green matter exists between the growth node and the lower part of the limb. With a sharp knife, girdle the limb a quarter of an inch below the growth node and then two inches below that. Remove all of the bark and green layer by scraping with the knife until everything is pure white. At this point you can leave everything for a few days, even weeks. Stage two is to apply a growth medium. The most commonly used medium is sphagnum moss (NOT peat moss). Once it is soaked it will hold moisture for a long time. Squeeze it well before applying as it does not have to be sopping wet. Bind the sphagnum moss to the wounded area using plastic kitchen wrap or aluminium foil, squeezing to remove as much air as possible. If you use plastic wrap you will need to cover it with towelling or a piece of an old T-shirt to protect it from the sun. Roots grow best in the dark. You can do the same with aluminium foil to stop it getting too hot or you can loosely wrap another layer of foil around the original. Foil can be twisted into place but plastic wrap may need ties at the top and bottom to keep it in place. Every two weeks or so you can open the top of the package to check that the sphagnum moss is still slightly damp. If it needs moisture it is best to apply water with a mist sprayer. Allow at least three months before you check for root growth. Allow at least six months before you separate the limb from the rest of the tree and transplant it. Besides providing moisture, roots anchor trees into the ground. Your new roots will not be strong enough to provide support so the new tree will have to be staked firmly. Alternatively you can put the new tree into a 5-gallon container of potting soil and surround it with a cylindrical tomato cage. Plastic ribbon can be used to anchor the tree, tying it to the frame on one side, once around the tree, then tying on the other side. Do this at two or three points and your new tree will not move when buffeted by winds. A plant produce from an air layer will not develop taproots so be mindful to keep it compact as it grows to adulthood. gardenerjack@coralwave.com