First wet chemistry results
from the Phoenix Lander shows that Martian soil is highly alkaline, and definitely interacted with liquid water at some point. The water isn't a surprise, but the alkalinity is - a lot of people thought that Martian soil would be highly acidic and, without being extensively modified, inimicable to plant life. Instead, according to the lead chemist,
in one of those quotes that the media loves, you might be able to grow asparagus in it. Yeah, but think of the shipping cost and the carbon footprint.
(Lunar soil, by the way, is suitable for marigolds