What does the cryptic crossword clue "Gardener needs these, otherwise eg ferns reign? (5,7)" mean?

The wordplay uses an anagram. anagram of EG + FERNS + REIGN? = GREENFINGERS The answer is GREENFINGERS.

Gardener needs these, otherwise eg ferns reign? (5,7)

Daily Mail Cryptic #16902 | 10 Down | 2022-08-15 flower