Should planter be "self-contained" or open at the bottom?
I want to build a cement block planter down one side of my driveway. So it would be about 2 feet high by 1.5 feet depth (inside measurement) by 40 feet long. On the house side, it would spread out to a big square planter next to the house that is around 6 feet on each side. This part of the planter would be about 4 feet high.
So kind of like this:
______________________________| | (This part would be 4ft high by 6ft by 6ft.)
This part about 2ft high by 1.5ft depth)
Should I leave the bottom of the planter "open" to the dirt (currently grass) below the planter? Or should I put plastic around the entire inside of the planter so it is completely self-contained and isolated from the dirt under the planter?
Also, how should I "fill" the planter? Should I just put regular dirt into it? Or rocks at the bottom, then some sand, and then planting dirt on top? Will the cement blocks "leech" out the water from the dirt?
I live in a warm climate (a Mediteranean island) and will have plants that don't need much water. I'll probably have an olive tree or small palm tree in the middle of the square part, and then small shrubs and bushes around it and down the driveway side. There will be a simple drip irrigation system on a timer to provide the water.
Thanks for any advice!