The most common and most likely answer to this crossword clue is the 3 letter word CRU
I've seen this crossword clue in The Times
C
R
U
More clues leading to the result CRU
Buddy explains!

The straight part
We know that "vineyard" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case vineyard = cru.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 CRU mean?
CRU noun- A vineyard or group of vineyards in France, especially one having a high reputation.