If you are willing to foot the expense, these tile blocks can be purchased at garden centers and home improvement stores. Rocks work just as well and also look beautiful and more natural and are much less expensive. I suggest using rocks, which you can buy or find yourself. You will also need a strip of plastic equal to the length of the border of your garden. The plastic is optional, but it eliminates weeds and it will save you a lot of time and backaches.
Cactus soil is also another necessity.
You will need enough to fill your garden to the top of the wall. You will have to wait until after construction of your garden to see how much soil you will need. You can purchase cactus soil at your local gardening center or home improvement store. If you cannot find any cactus soil, you can make your own by thoroughly mixing two parts potting soil, two parts sand and one part gravel. The first step in building your garden is to cover the edge of the grass with the strip of plastic.