The most common and most likely answer to this crossword clue is the 14 letter word GREEN-FINGERED
I've seen this crossword clue in The Times
G
R
E
E
N
-
F
I
N
G
E
R
E
D
More clues leading to the result GREEN-FINGERED
Buddy explains!

The straight part
We know that "Like good gardener'" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case like good gardener' = green-fingered.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.