But most likely they would just melt the water ice that is already on the planet.
And they would bring the microbes with them. Actually we have no choice about bringing them.
A few packets of the correct microbes, some heat to melt the water ice and some earth worms.
Potatoes.
Now developing a sustainable cycle would be more difficult. A great deal more difficult if not impossible. But if you just want to grow a few plants it is not that hard.
Mars HAS water in the permafrost.
My OTHER kid, a geologist, was the first to analyze the photos from the Mars Orbiter and recognize that Mars had glaciers only a few million years ago.
Ironically, when Mars orbit changes over time, it warms up. That is when the permafrost outgases enough water to form glaciers. When Mars gets colder, the glaciers sublime away and the water is again locked up in permafrost.
My son was the FIRST to publish a paper on Martian glaciers, although the MSM did not pick up on it until NASA had a press conference.
If we sent the crabgrass that ALWAYS grows in my lawn, they would inundate the planet in less than a month.