Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
An inch is not really enough to hold the plant roots on any but the very smallest plants, and even these will develop better roots in deeper substrate.
I usually put enough substrate at the front to be a bit higher than the bottom rim (so that might be an inch or so) and slope it toward the back, with deeper mounds behind rocks or driftwood. These deeper mounds are more like 3-4" deep.