The drain hole may or may not be adequate, depending on the soil you choose. I think you'd be making a big mistake to use topsoil, even the best garden soil. Any soil that compacts readily will likely clog the drain hole, even with a large mesh screen over it, unless the container is raised so you can keep it cleared. Use a good quality container soil that drains well & holds good volumes of air. This might be a case where some sort of filler material is appropriate in the container bottom if you don't wish to use nearly a yard of soil. You might also check with any local nursery operations to see if they'll sell you some of their potting mix, or look around on this forum for suggestions on how to build your own container soil.

Al

Thanks, Al!