[robocat]

There is a vast range of non-native eadible plants and animals that have now been introduced to every country.

That would make a huge difference compared with traditional indigenous societies. However farming does require steady state weather - which is unlikely after a nuclear war?

[XorNot]

There still isn't enough to sustain people on subsistence farming. And subsistence farming, is well, subsistence-level - it precludes specialization which means it precludes most of the advantages technology brings us today.

If you're ever in a civilizational collapse scenario, literally the most important thing you can do is rapidly restart the farm supply chain by whatever means necessary - anyone imagining building a fortress for themselves is building a tomb.

[PeterisP]

Subsistance farming for a limited number of people can be done by burying potatoes in the ground and digging them back up in the autumn. Well, it's a bit more to get a good yield, but not that much more, you can (and some places do) teach that to literal kindergartners in a single day. We can't sustain 7 billion of people this way, but if some catastrophe kills 99% of humanity, the availability of better cultivars makes subsistence farming for the remainder much easier than five hundred years ago.

[arethuza]

Subsistance farming based on potatoes is not without its risks:

https://en.wikipedia.org/wiki/Great_Famine_(Ireland)