[runholm]

"While Venus’s surface is awful, its upper atmosphere is surprisingly Earthlike. 55 kilometers up, a human could survive with an oxygen mask and a protective wetsuit; the air is room temperature and the pressure is similar to that on Earth mountains. You need the wetsuit, though, to protect you from the sulfuric acid."

https://what-if.xkcd.com/30/ (not quite a scientific source, so make what you want of it)

Maybe if your plants can deal with the acid you might be able to do it. (I am not a biologist, chemist or anything relevant to answer this question, this is just my best guess).

[sohkamyung]

Exploring the atmosphere of Venus has been considered. Here's an article on it [1]

[1] "NASA Study Proposes Airships, Cloud Cities for Venus Exploration" http://spectrum.ieee.org/aerospace/space-flight/nasa-study-p...

[mirimir]

Some bacteria would be OK with that.