I recently tried to put together a container garden of perennials on the south side of my home. The goal was to container a variety of decorative plants - to keep water away from foundation, reduce annual planting, and overwinter in our garage or 3 season porch. in the end, I am not pleased with it. I'm in Illinois, zone 5, a semi-urban area, with very little yard that is not heavily sloped. I am thinking of replacing the container with a raised bed. I have a 2 foot wide, 6-7 feet long area to convert. I am raising lavender, walkers low catmint, rosemary, April and may night salvia, dianthus, sun heuracha, and ornamental grasses. Pic is attached. Question: 1. How deep should I make the bed for these plants to yearly continue growth? I was thinking 24" or taller? 2. Will depth or material (wood versus metal) affect the overwintering? 3. can I use rock for drainage at the bottom of the bed, covered by a clay soil with dead grass lumps in it (that I dug from the perimeter of my yard and want to use to get rid of it lol, and for additional filler) followed by a good planting mix? 4. How to overwinter flowering perennials in a raised bed: do I cut back and cover with coir or design a hinged system or dome with heavy plastic/greenhouse plastic, or just cover with plywood? Thanks for any help!