The most common and most likely answer to this crossword clue is the 4 letter word KENT
I've seen this crossword clue in The Times
K
E
N
T
Buddy explains!

The straight part
We know that "English architect and landscape gardener" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case english architect and landscape gardener = kent.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 KENT mean?
KENT verb- To know, perceive or understand.
- To discover by sight; to catch sight of; to descry.
- A shepherd's staff.
- A pole or pike.
- To propel (a boat) using a pole.