One effective method of gardening in a spot with subpar soil is to build a raised bed, and as these videos show, they can also be built from scraps, and in a way that allows the garden beds to water themselves.
Trying to grow food in a spot with low quality soil is a fairly common gardening challenge, especially in backyards of new constructed homes, where any topsoil has been scraped off before the construction begins. These yards are often compacted from all of the heavy equipment and building activity, with little to no soil fertility or biological activity, which can be quite frustrating, even for seasoned gardeners.
In other places, such as urban areas, there is a very real possibility of soil contamination from a variety of sources, which is usually not visible to the naked eye, and which could lead to either poor growing conditions or health hazards from eating the plants grown there.
In both of those cases, raised garden beds are a great way to get around the limitations imposed by the soil issues, and can yield greater soil fertility and bigger harvests, along with allaying health concerns from polluted soils. Raised garden beds offer some other advantages as well, in that they are often easier to work with for people that have a hard time getting down to ground level, can keep invasive weeds or grass out of garden beds, may extend the growing season (the soil warms up earlier in the spring, and can be easily covered as fall approaches), make for a neater and easier to maintain garden, and can also address other soil conditions such as lack of good drainage.
To take the raised garden bed concept one step further, it's possible to build them as wicking beds, which will greatly reduce the amount of time it takes to water them (virtually eliminating one regular garden chore), as well as reduce water consumption in the garden beds by as much as 50%. There are commercial raised wicking beds, self-watering containers, and container gardens on the market, which are convenient for those who want instant gratification, but for those of us on a strict budget, building a DIY wicking raised garden bed can be affordable and fairly simple to do.
The folks over at Food is Free have a helpful (and humorous) video guide to building your own raised wicking beds from mostly scavenged materials, which is well within the abilities and resources of even the most DIY-challenged person. Here's the concept:
The materials used for this DIY wicking raised garden bed project include old shipping pallets (a common urban waste resource), corrugated plastic political signs (probably the best use of these yard propaganda items I've seen in a long time), and crushed glass (often available from local landfills, but if not, pea gravel could be used instead), some pieces of PVC tubing, and a tarp.
Here's the DIY guide, complete with ukelele:
It's important to note that you should always steer clear of pallets that have been treated with methyl bromide or other fumigants that may transfer to the soil (here are two good primers on what to look for). If you are concerned about the possibility of potential leaching from the tarp or other materials, you could invest in a pond liner instead, replace the PVC drainage pipe with irrigation line or bamboo, and use scavenged boards to line the interior of the raised beds instead of the political signs (simply to keep the soil from spilling out of any gaps in the sides).
For another great resource on wicking beds, Verge Permaculture has a pretty comprehensive DIY article that can help guide your efforts.