By now you've probably heard the big news from Mars. Phoenix has learned that the Martian soil is considerably more friendly to Earth plants than most scientists thought—somewhere around seawater or baking soda in alkalinity (alkalinity is a measure of how basic, as opposed to acidic, a substance is). The soil was also found to contain essential minerals such as magnesium, sodium, potassium, and chloride. It is unknown yet whether other chemicals such as nitrogen or sulfates are present, but tests will be conducted soon.
The funny thing is, everywhere I read about it they seem to use a different vegetable as an example of what might be able to grow in Martian soil: asparagus, green beens, turnips, etc. More acidic plants, like berries or tomatoes, would not grow in soil with similar composition to the soil found on Mars so far.
The presence of these elements and the lower-than-expected alkalinity are good news, but that doesn't necessarily mean that when we land a colony or research station on Mars the astronauts will be able to grow food. After all, soil composition for different regions of Earth can be radically different. One would expect the same on Mars.
Further analysis of the Martian soil should provide more information and could possibly give us some more surprises like this.