Today, I received an interesting comment from Anne WALKER on my former posting :
Different aspects of rooftop gardening (Google Alert / Salt Lake Tribune) July 13, 2007
” If a garden can be grown on a roof top, how about on the parking lot of an old abandoned strip mall. It is late in the season to start a garden, but we just received funding. We also have donated space in a building located in a strip mall. There is a fenced in area that I’d like to create a few raised beds and perhaps apply lasagne gardening in the beds. What do we do about drainage? How do we keep the soil and water from running out under the beds. Do we line with plastic? Help!!! This is a late summer youth project, funded in part from Community Block Grant and State arts funds.”
Here is my reply to her :
Thanks for contacting me and congratulations for your nice ideas.
Raised bed gardening offers a lot of opportunities to embellish our environment or to grow plants in any “difficult” place.
Let us first consider the outside parking lot (or is it inside ?). I see no problem to install raised beds there. Would a bit of water running out be a problem ? Then, I recommend to make the beds a bit higher (1-2 feet), to line the bottom up with a strong plastic sheet forming a shallow reservoir, to fill the bottom part of that reservoir (2-4 inches) with granules of expanded clay (also used in hydroponics) and to cover these granules with a good potting mix to which I would add some water stocking polymers or, even better, a soil conditioner like TerraCottem (see <http://www.terracottem.com>).
About the raised beds inside the building : see above, as I cannot foresee any problems with water.
Let me now make another suggestion !
Why don’t you construct a raised bed and fill it up with containers (each of them perforated at its bottom for drainage). I am thinking at the classical plastic flower pots, but also at PET bottles or even big plastic party cups (use your imagination).
The raised bed should be constructed like the one described above : with plastic lining at the bottom, but without clay granules. The containers (pots, bottles or cups) can be put directly on the plastic sheet (in the so-called reservoir) and filled with a good potting mix (mixed with water stocking soil conditioner), then seeded or planted. Now all the containers are covered (mulched) with a thin layer of potting mix, so that one cannot see the containers anymore (only a nice layer of soil under which the containers are hidden). When watering such a raised bed, most of the water will be running into the containers and stocked in the polymers. A surplus of water, running through the containers or through the open spaces between the containers, will run into the plastic sheet reservoir and only a minimum will be kept for a short time on that plastic sheet (from where it will be gradually absorbed by the potting mix in the perforated containers).
I can imagine that after a while one would have to add a thin supplementary mulching layer of potting soil, for the soil will slide partly down into the open spaces between the individual containers.
I never did this before, but I can imagine that this would be quite successful. Worth trying, I think !
Please keep me informed and possibly send me some photos of your realization. I will gladly publish them on my blog.