Actually that isn't true Martyr. Even with all the radiation plants would still grow, as well as animals. Of course they wouldn't be edible because of the radiation that they would absorb, if you look at how many nukes were set off in Bikini Atoll and the plants and animals there still thriving. While some plants and animals may die off, many more will survive and thrive filling in the wholes left in the ecosystem to long as a major keyplant/animal isn't lost. Though of course this matters little, as we are talking real life with that bit and not Fallout Science that dictates life in Fallout. Of course there are living plants in the original Fallout's so it really was just Bethesda's decision to make the Capitol Wasteland as bleak as possible.
That's what I'm doing. I don't use real world science to describe Fallout's world. I'm stating what has happened in game. Also, it is true there are living plants, but aside from Shady Sands, who got their crops from a G.E.C.K. most of the plant life is inedible, being weeds or other inedible plantlife that simply exists. As for animals, what I'm saying is true, it's basically been explained that the black rain DID happen, and that those animals and people outside when it happened died from the toxisity of it.
Also, I never said that plant life DOESNT exist, I stated, quite clearly, that the plant life that DOES exist is hard pressed to exist in it's own corner let alone expand into the world. It's why I hope Harold's seeds spreading across D.C. is canon so we can see it revive with plant life.