What does the cryptic crossword clue "Should a vegetable grower know his well? (6)" mean?

The definition is "Should a vegetable grower know his well?". The wordplay uses a cryptic definition. Cryptic definition The answer is ONIONS.

Should a vegetable grower know his well? (6)

Independent Cryptic #11843 | 8 Down | 2024-09-24 flower