Large planter and wicked beds
I am building some 14' x 4' planters out of cinder blocks. My wife and I are getting on in years and it is difficult to work low down. I have decided to build them about three feet off the ground. This presents both problems and opportunities. I now have a large space under the six inch soil bed ( I'm using the square-foot gardening method which calls for very little soil ) that is empty space. I would like to fill this space with captured rain water from the roof. Thinking it over, it struck me that I could use the water directly to water the plants via some sort of wicked bed design.
My questions are:
*) How can I do this and
*) is this a good idea?
I frequently see small pots or planters that are "self-watering", but never a larger flower bed or planter. Is there some reason people don't do this? What are the down sides to this technique?