3' tall planter, false bottom drainage
I want to build some planters (for perennials, not veg) along my back fence that are around 3' high. I will also have some that are 2' in front of the taller ones. Probably about a foot wide, and they will span about 35'. Because of the pressure that amount of soil would cause, as well as cost, I want to build a false bottom in them. This would make the actual bed about 12" deep, but look like it is 3'. I a few questions regarding this.
1. is 12" a good depth for these kinds of plants? Would you suggest deeper/more shallow?
2. Drainage. What do I do? If I drill holes, how many? Wont the soil fall thru it? If I drill holes, line with weed barrier and then soil, will that be good?
3. Given the shallow nature of this planter, I should be able to build one giant, long planter, correct?
My house is very modern with clean lines, hence the design of these planters.