The most common and most likely answer to this crossword clue is the 8 letter word HONESTLY
I've seen this crossword clue in The Guardian
H
O
N
E
S
T
L
Y
More clues leading to the result HONESTLY
- Home in sacred surroundings? Well, really!
- Saint, fifty, in love — well!
- Straight home in divine surroundings
- Pious in retreat? On the contrary, in truth
- Really religious nursing home
- Plant encircles lake? No kidding!
- Genuinely pious keeping comfortable home
- Perfect life initially occupying dirty home — really?
- Really sharpens ends of tool facing yard
- Fairly religious assuming sanctuary
Buddy explains!

The straight part
We know that "Plant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case plant = honestly.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 HONESTLY mean?
HONESTLY adverb- (manner) In an honest manner.
- Frankly, to be honest.
- Used to express exasperation, dismay, etc.