Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
It is almost impossible to plant without mixing, so I do not do layered substrates.
However, if dirt with gravel cap is your goal, then there will not be much mixing. Most of the gravel will get pushed sideways, especially if you move slowly when you are planting. Only a little will end up mixed with the dirt unless you are really careless and just shove the plants in any which way.