Idk. The body seems to adapt to radiation and some excess guardian genes may prevent malignant growth. Of course you cannot live through the gamma blast area, but surely the fallout zones may be manageable.
On the other hand chemistry is highly temperature sensitive and at some point proteins will just denature. Then again you cannot have rapid growth without water, as plants need evaporation to transport minerals and such from the soil into the plant. And what about phosphorus anyway? Soon most soils may be nothing but dirt. You cannot work around the phosphorus erosion. Once it's lost, it's lost. We better start recycling our feces and the dead now. You kinda need to harden all life, not just humans and crops.