I would like to start a vegetable garden. The problem is I've planted so many fruit trees in the ground that there's no more room for vegetables. The only way I can start my vegetable garden is to place it over the concrete in my back yard. The natural choice for gardening on hard land would be elevated planters:
But these elevated planters are just so darn small and darn expensive (~ $200). On the other hand, normal garden beds are usually much bigger and cheaper. I'm considering getting this behemoth:
The problem with garden beds is that they don't have a bottom. What precautions, if any, should I take with the bottom if I were to put this garden bed over my concrete? Will drainage be poor? Will I need to cover the bottom with something? Do vegetable roots not like hitting into the concrete?