I have three young lavender plants that I am planting around my mailbox. However when I started digging, about two inches below the surface in precisely the spot the first plant needs to be placed, is what appears to be a sawed off sign post. It's not very large so I'm wondering if I'd be able to plant the lavender over top of it if I gently spread the roots a bit? Would this harm the plant at all?

If planting over top is a no-go, what are my options? It seems very deeply seated and doesn't budge side to side at all.