This is not how radiation works on vegetation.

First: The "Wasteland" from Fallout goes back to Black Isle, but on the other hand a lot of the first two games play in the desert. Still, Bethesda did not invent the "nuclear wasteland devoid of plants", but Bethesda chose to let their later parts play out in far more fertile lands.

Nukes do not sterilise a land for decades to come. This is simply not how the physics works.

Check out images, do a google image search, how the land around Tschernobyl and Pripyat look today: Overgrown. Very, very overgrown.

Nukes burn the forest, but stuff grows back very fast.

No, even though plants grow, it is not recommended to eat fruits from contaminated sites. ;)