Growing plants on Mars: Necessary or even possible?

So I have been reading The Martian by Andy Wier for the third or fourth time, and I have been thinking. For all the amazing scientific accuracies in the book, from nuclear powered baths to explosive water making, the one part that seems to be pushing it is Watney's potato farm. I get that he is a botanist and all but growing food with nothing but feces and red dust seems like a stretch. So let's look into the facts and science the sh*t out of this.

Growing conditions

Mars is a tough place, us resilient humans need tonnes of life support to even breathe on the red planet, so how would plants be able the spread their leaves. First of all the pressure, if a bowl of petunias randomly appeared on Mars its internal pressure compared to the near vacuum of mars would send scraps of petal and leaves flying everywhere in a small green explosion. So whatever greenhouse we build on Mars would have to be pressurized and hopefully protected against solar radiation that would rip apart our poor plants DNA. 

Next of all, light, all plants use a handy little process called photosynthesis to create glucose, but bonding all those atoms together requires energy, and on earth they get said energy from the sun. Mars is 50% further away from the sun compared to earth, but thanks to the inverse square law it receives 44% of the light. And this isn't accounting for the planet wide dust storms that Mars is frequent to, yet another problem faced in The Martian.

To counter this, researchers attempting to grow plants in MSS (Mars Soil Simulant) used LEDs to enhance growth in their crops, and reduce light as the limiting factor. One problem down, onto the next.

The Perchlorate problem

Apart from the environmental conditions on Mars, the soil (or regolith if you want to be fancy) poses some problems. One of these is the prevalence of heavy metals like calcium perchlorate, which has the nasty tendency to build up in our bodies and cause problems in the thyroid gland that controls metabolism, so yeah, you don't want this seasoning on your veggies. But we can turn this problem into a potential solution for the lack of oxygen but introducing certain microbes into the soil. These microbes ingest perchlorates and release oxygen, killing two birds with one stone, if there were any birds on mars.

Martian soil may have many nasty surprises for us, but in 2018 it had a far nicer surprise. Using its sampling drill and mass spectrometer, Curiosity detected semi-complex organic molecules on Mars. The same molecules that early plants broke down for energy before photosynthesis. This was a major event as it suggested that plant life might of survived in the distant past of Mars. It's also good news for Martin farmers as it solves the pesky sunlight problem.

But why?

Why go to all this effort for some fresh fruit and veg? The benefits are numerous and not just because once you have grown food in a new place you have technically colonised it. Sending things to Mars is expensive, around $2.78 million per kg, so if we can reduce the weight we send with our astronauts we can reduce cost and complexity. The benefits on your mind of eating fresh food are numerous and the developments made in this endeavor may benefit food production here on earth.  The main reason in the long term is to make our colonies self sufficient, the goal of the man spearheading our martian exploration, Elon Musk. And if he deems this important, I think we should too.