In the winter, a fig tree appears dormant because it has shed its leaves and isn’t receiving any energy from the sun. We may  think that the whole tree is dormant but this is actually not true.  After we harvest the figs in the fall, sugars made in the leaves were transferrred to the shoots, trunk and roots for storage. A large porton of these storage compounds are stored in the roots. The roots use this abundance of energy for growth when the conditions for growth are favorable.  In other words, the roots remain mostly active and grow during winter months whenever soil temperatures are at least 40°F. The potted fig tree in a garage has warmer soil temperature than a fig tree growing in the ground. Therefore, we can do air layer from the potted fig tree during dormancy, we do not girdle the branch because the energy storage in the roots will transfer to the air layering for it to take roots and remember to use a fresh potting soil in a bag method by Leon Edmond. By keeping the soil in the pot slightly moist and the only way for the tree to absorb nutrients and moisture from the air layering soil is sending its energies there to make roots . Good luck to those who do air layers from a potted fig tree during dormancy.

This is the link to that thread:

http://figs4funforum.websitetoolbox.com/post/can-i-do-an-air-layer-in-the-winter-or-does-it-have-to-be-6550718

Best,
Tam