I guess a hydrogen nuclear bomb (fusion) could be called a super nuke.

Look, in our world a salted nuclear weapon (dirty bomb) would make the land immediately around ground zero uninhabitable for at worst 120 year. The most common salting materials are cobalt and strontium, with effects lasting from around 20 years and 90 years respectively. in our world, general fallout would only be a hazard for a few weeks except in non-ground zero hot spots, where the danger could last for a few months.

In our world, jumping from a tall building in a suit of power armor would leave you as a puddle of goo inside the boots, even if the suit remained intact (which it wouldn't).

The Fallout universe does not follow the principles of science like our universe does. It follows the principles of SCIENCE!

But the real reason that all the vegetation in the Fallout series is brown is artistic. Browns make the wasteland seem more desolate than greens would. But cheer up. There are mods that turn the wasteland green. If you play on a PC you can use them now, If you are a console player you will be able to use them soon.