Where can you find the fruits of the nightshade? (The Witcher 3: Wild Hunt)

I didn’t find either. Apparently after some task they will appear.
I understand you need to craft red mutagens?

yeah

Simak Shekoyan
you haven't completed the main plot yet?

Pepin3d
failed

I don’t want to spoil it, take a look, there’s like a hint
Spoiler advice to go through the main plot
and then you will not need this nightshade anymore

4 nightshade grows in Corvo Bianco, in the garden, more specifically in a greenhouse under a canopy

Nikotinoz_
heh, it is clear that the ATP
campaign does not grow anywhere else, although you still have to run around
and, uh, until you put some money on the garden in the estate?

upd: I checked the early preservation and it became clear that nothing was growing there before the dough was invested in Curva Bianca.