The most common and most likely answer to this crossword clue is the 9 plus 7 letter word BOTANICAL GARDENS
I've seen this crossword clue in The Guardian
B
O
T
A
N
I
C
A
L
G
A
R
D
E
N
S
Buddy explains!
The straight part
We know that "Grounds/Grounds" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case grounds/grounds = botanical gardens.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.