Judy Hsiao, of California, is an experienced grower of many trees as well as an avid bonsai grower. She did an air layer of a Ficus burtt-davyi in the spring of 2009 in the usual manner by removing the bark. She got too busy to finish the layer and did not get to put moss around the layer and then cover it with plastic. She just forgot about the girdled Ficus. In July the roots started showing at the girdled area. Through Ausgust the weather remained warm and humid and watering was done as usual.
"I also placed a ceramic disc that I made two  more years ago after I started doing ceramics. I have done this before by using half inch pine wood, cut two inch by two inch and drilling some holes in the wood. I have used the wood board with pines by spreading their roots over the board as well as securing the tree down to the board. Prior to using the board I would often use a broken piece of ceramic to place under the roots. PS, as you can see the ceramic I made is not flat but has a center a dome. This process with wood or ceramics allows the tree to develop a nice flat root base."

Comments:

Judy, has shown us that doing an air layer in a two step process works quite well. On other varieties of trees that are debarked roots will not form in the air but a callus will form. This "layer" can be cut off below the callus and roots much more easily than a cutting for some difficult to root materials.

The second trick of using a flat material of some sort beneath the roots helps the tree to form a good, flat root base.

Thanks to Judy for her sharing her ideas.

Bottom of tree after the top was removed

Ficus top with roots - ceramic disc on the table.

Ficus burtt-davyi roots spread evenly over the disc

Ficus planted with support sticks and note the fig fruits!