Growing Plants in Martian Soil
Since the air is not what we are used to, any human visitors to Mars would probably have to live for long periods in their landing craft, returning to the orbiter to replenish oxygen, food and water supplies on an almost daily basis. The initial landing site, or base, would take some time to build and the orbiter would provide safe haven for the astronauts as they begin their stay on Mars. But what of plant life? Seeds have already been sent into space to be germinated and the experiment was successful. It can be done! With the right equipment, the Martian water could be made useable for both humans and plants. As the water works and greenhouses are constructed, the hydroponic gardening could begin aboard the orbiter. Sturdy greenhouses to protect the crops from ultra violet rays and Martian weather fronts might take some time to build. During the building, the seeds would grow and be seedlings when first placed into the greenhouse.
Discovery Channel* seems to think that asparagus would be a good crop for the Martian soil, considering its levels of alkalinity. The soil is far less acidic than was originally expected according to the BBC. Other crops that require alkaline soil might also do quite well (the astronauts would get really tired of a straight asparagus diet!). Some of the soil samples appear to contain perchlorate, which is highly oxidizing, while other samples don't show it. So the astronauts on Mars would have a supply of food and water, depending either on the location of their planting or the additives they bring to improve the Martian soil.
The MECA (the Microscopy, Electrochemical and Conductivity Analyzer) from the Phoenix spacecraft, has found significant amounts of perchlorate in the Martian soil. This could be a huge problem for farming. Asparagus, beans, broccoli and other vegetables that should do well in the elevated alkaline soil would not survive being planted if perchlorate is present. This may or may not be a problem, because as the Earth has some areas that are better for growing one crop and areas that are better for another (due to their chemical make-up), Mars could well be the same. It is possible to use additives and fertilizers to counteract some harmful elements and NASA has yet to determine how much the perchlorate would actually affect a farming operation.