The conditions on Mars are very hostile towards plant life. The planet lacks water, fertile soil, and most nutrients necessary for plant growth.
While this could be fixed by bringing nutrient-rich soil from Earth, that process would be much more difficult and time-consuming than growing crops in nutrient-starved martian soil in the first place. In addition, any food produced by Martian plants would need to be supplemented with protein from animals since there are no martian animals native to the planet.
Given these conditions, planting strategies would need to be extremely careful when creating food sources on Mars. Humans would need to bring all their necessary resources with them when they settled on the new planet. In addition, they would need to remain vigilant about maintaining the environment needed for plant growth. This would require constant effort by human hands since no naturally occurring elements sustain martian plant life.