So, what should we grow on Mars?

 We've got those pesky perchlorates, salty soil, and no helpful microbes. What will grow?

The first crops on Mars would be soil creators. And the key crop is...alfalfa.

Alfalfa is a fodder crop typically grown to feed livestock. What you do is grow alfalfa, then plow it back in and grow turnips, radishes and lettuces. It will grow in  simulated Martian regolith as long as we flush out the perchlorates (we need something which eats perchlorates, dang it).

Water on Mars will need to be desalinated.

Alfalfa could also be used to feed livestock, but only two major livestock species are feasible due to their size: Rabbits and guinea pigs. Sorry, Martian colonists, if you want meat you'll have to eat Thumper.

Other food crops could be grown hydroponically if we can get the water desalinated.