How deep should a border be (i.e. under the surface)?

Question

Our neighbours had an oil spill last year. Most of the damage was at our side. Eventually the loss adjusters agreed to pay up, the garden (lawn) has been dug up and all contaminated soil removed, all is about to be reinstated. My question is: the lawn area is now going to be 30 cms topsoil and underneath is over one metre gravel/stone. We were intending to have a border at the lawn area. Is 30 cms adequate?

Answer 1

If you mean a plant border, that will likely not be deep enough for ornamental plants if there is gravel below. It will be fine for grass, but most most ornamental plants need about 1.5 times to double that in the ground - more if you are planning on using trees or shrubs.