Mistake 4. The most serious mistake. The shelf is flat. Those planting baskets look unsightly. What I should have done is made the shelf less deep then dug out a planting channel which could be filled with soil after the liner is installed then place an inch of gravel over the top to stop the soil escaping.

After a change of plan it was not necessary to step the sides like this as I raised the edge about a foot or two from the original edge. But, I made the same mistake again.