Podzol can generate even if there is a air gap to the dirt and also if there is another dirt block above it.

Steps to create:

1. make a 3 block tall pillar of dirt 
2. remove the bottom dirt block from the pillar
3. from the pillar skip 1 block in any direction and plant spruce saplings in a 2x2 space
4. bonemeal saplings to grow 2x2 spruce tree
5. podzol will generate on the 2nd dirt block even though there is a air gap and another dirt block ontop