The most common and most likely answer to this crossword clue is the 6 letter word OXLIPS
I've seen this crossword clue in The Times
O
X
L
I
P
S
More clues leading to the result OXLIPS
Buddy explains!

The straight part
We know that "plants" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case plants = oxlips.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 OXLIPS mean?
OXLIPS noun- The plant Primula elatior, similar to cowslip but with larger, pale yellow flowers.