Soil depth for Mother of Thyme
We're digging up our cruddy Reno dirt (sandy/rocky) and replacing it with topsoil in preparation for spreading ground covers. While we're doing four inches in most areas, there's a disagreement for the spot where Mother of Thyme is going (Thymus s. coccineum). I say we still do four inches, she she says only two inches is adequate.
Can anyone help settle this?
(Yes, I know, it sounds insignificant, but every inch adds up. This is a rare case where I'd be happy to be wrong.)