Getting to Mars on chemical rockets is not that bad, especially if you can accept a launch window every 15 years. Getting people to and back from low Mars orbit with chemical rockets on a more flexible schedule takes a lot more fuel. It’s clearly viable, but for that kind of DeltaV across such a long trip, solar powered Ion thrusters have several significant advantages.

As to growing food, for on a single mission it’s not that critical, but if you’re sending several missions to Mars unused supplies from one mission can be used on the next mission. Further, the difference between survival and comfort adds up to a lot of food.

You can go every 26 month. If you can produce fuel on Mars going back is way easier then going from Earth to Mars. You don't go from Mars Orbit, you take of from the surface directly to earth where you aerobrake. No Orbit operation on Mars needed.

> It’s clearly viable, but for that kind of DeltaV across such a long trip, solar powered Ion thrusters have several significant advantages.

Not really. The only potential use for ion thrusters is for cargo transport that is not time depended. If you do that you need to figure out how to do the landing, so the complexity is just higher. The thrust is just to low compared to a few powerful chemical engines. If you can refuel in earth orbit for cheap you are gone be way better off with chemical.

If you move on from chemical, nuclear thermal is by far the best option.

Food is really not the problem. The mass of food needed for humans is pretty small. Clearly you want to produce food on Mars eventually but its not a priority for the first 5 to 10 years. Refuel on Mars is by far the biggest mass saver.

Individual ion engines have been built up to 1.1 lbf for 100kw. Over 2 weeks that’s 9.8m/s * 60 * 60 * 24 * 14/ mass that’s 1.2 km/s for a 10,000 lb spacecraft. And nothing says you can’t use more for a larger spacecraft.

For comparison the ISS’s solar panels are over a decade old and still generate 240kW in direct sunlight. So, you could easily reuse those panels for multiple trips, though power output is cut in half near Mars.

Cheap Mars launch windows are every 26 months, not 15 years.

Cheap is relative, Earth years and Mars years don’t evenly divide, so the 26 month cycle is fairly good but not optimal if your willing to wait.