This year my spousal accessory unit and I have been engaged in a limited trial of upside down gardening. Three varieties of tomato plants (grape, celebrity, big boy) were planted in late May (late planting to be sure). 
The planters were sourced from a garden supply house, but 5 gallon buckets would have worked just as easily. We used hot house starts that made the start up extremely cheap, generic potting soil was used as the base. The total cost was about $30 and two hours labor.
An, a-frame was constructed that can be adapted to hold up to 9 plants. Currently the three plants occupy a space about 5X7 feet. In that same space you could easily grow 9 or more plants by using cross braces extending away from the center. Some of the easily seen benefits is the near absolute zero infestation of the plants by bugs, rabbits, or other varmints. The second great benefit is the zero need for weeding.
The plants have already produced way more vegetables than the total cost of producing the a-frame and buying the starts. If we had started with seeds the cost would have likely been even less. Another benefit is this is a do it and ignore it kind of gardening. Other than watering it fits into a hectic suburbanites schedule fairly easily.
We could have set up a rain-catch system and likely watered from that through most of the spring and early summer. I mention this to show that the most resource intensive portion of the project (water) could also be basically reclaimed water that would normally run off. I realize it is not zero impact (what was using that water before?), but it is a lot lower impact on my wallet. Water catch systems are simple and cheap. We didn’t set up a rain catch this year but may do so next year. The late summer in northern Indiana has had little rain, but even then the watering is easy and substantially less water is used than a normal garden plot may require.
In the picture you can see the bottom cross bars can be used to support potted plants that are shade tolerant. For our purposes though plants like tomatoes were our primary interest. Next year we plan adapting the plan slightly spanning out to 10 feet wide, adapting some tomato cages, and trying to grow squash and cucumbers upside down. Another plan is to try and mimic some of the air gardening methods used at Disney World though many of those appear to be energy intensive. Though, we would still like to create a pumpkin tree if possible.
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This is great info! I’ve never seen this in action and would love to do something similar in our community garden plot. Thanks!