1) Earth microbes and soil organisms (worms) can live in hydrated martian soil. (https://news.nationalgeographic.com/2017/11/mars-soil-earthw...)
2) Food plants can grow in martian soil that has had said organisms added to it.(https://www.nasa.gov/feature/farming-in-martian-gardens)
3) The water to hydrate the soil is already on Mars.(this article)
4) We can build an artificial magnetosphere[1] to protect an area from solar radiation.
So one trip to Mars that can land a small (< 100kW) power plant, organic amendments, tools, and material for a pressurized green house will be able to create a 'farm' on Mars. That is pretty neat.
[1] They designed it for spacecraft propulsion but it has the effect of a shield if installed in a ground station. http://earthweb.ess.washington.edu/space/M2P2/theory.html