The most common and most likely answer to this crossword clue is the 10 plus 5 letter word CAPABILITY BROWN
I've seen this crossword clue in The Daily Telegraph
C
A
P
A
B
I
L
I
T
Y
B
R
O
W
N
More clues leading to the result CAPABILITY BROWN
- 9 21 downer to limit PM’s inspiring skill
- Efficiency personified in tanned gardener
- Garden designer covering a part around one lake with variable colour
- 17 to surpass skill British possess
- Gardener’s headwear means forehead ultimately unseen
- International sportsman with skill getting bronze — he enhanced many grounds
- Gardener with top rating, one landed gentry ultimately toast
Buddy explains!
The straight part
We know that "he enhanced many grounds" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case he enhanced many grounds = capability brown.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.