The most common and most likely answer to this crossword clue is the 8 letter word LETTUCES
I've seen this crossword clue in The Daily Telegraph
L
E
T
T
U
C
E
S
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 = lettuces.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 LETTUCES mean?
LETTUCES noun- An edible plant, Lactuca sativa and its close relatives, having a head of green and/or purple leaves.
- The leaves of the lettuce plant, eaten as a vegetable; as a dish often mixed with other ingredients, dressing etc.
- United States paper currency; dollars.
- A strong yellow-green colour, like that of lettuce (also called lettuce green).