Same as the other use of the word "fast". "Quickly" is the more natural adverb to use here. The raspberries are growing quickly. As the plants themselves do not go running around the fields. ;)
Raspberries grow quickly, how is this not acceptable? Also there is no need for "The" either here
'Raspberries grow quickly.' should be accepted.
I agree, so does my Finnish husband!
Definitely quickly, not fast.
"Fast" is also perfectly fine, but "quickly" is a bit better indeed.
Even though the word "fast" is sometimes used interchangeably with "quickly" in colloquial English, the more technically correct word choice would be "quickly" in this context.
[I have also reported that "quickly" should be allowed]
"Raspberries grow fast" should be accepted.
More correct English would be the raspberries are growing quickly.