The most common and most likely answer to this crossword clue is the 4 letter word ADAM
I've seen this crossword clue in The Times
A
D
A
M
More clues leading to the result ADAM
- A mother? He didn’t have one!
- Water, or where to buy something to hold it?
- Fellow US attorney visiting a medium
- Notice alpha male is first man
- What’s designed to hold back architect of Scottish nationality
- First person to make precocious girl lose head?
- First male attorney to stand up in the morning
- God's first son on Jesus' first morning?
- First man, first male to forsake brothel-keeper
- Check on a Scottish architect
Buddy explains!
The straight part
We know that "expelled gardener" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case expelled gardener = adam.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.