The most common and most likely answer to this crossword clue is the 9 letter word HOTHOUSES
I've seen this crossword clue in The Daily Telegraph
H
O
T
H
O
U
S
E
S
Buddy explains!

The straight part
We know that "nurseries" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case nurseries = hothouses.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does HOTHOUSES mean?
HOTHOUSES noun- A heated greenhouse.
- An environment in which growth or development is encouraged naturally or artificially; a hotbed.
- A bagnio, or bathing house; a brothel.
- A heated room for drying greenware.
- A hot state in global climate.
- (of a child) To provide with an enriched environment with the aim of stimulating academic development.