The most common and most likely answer to this crossword clue is the 8 letter word WREATHED
I've seen this crossword clue in The Daily Telegraph
W
R
E
A
T
H
E
D
More clues leading to the result WREATHED
Buddy explains!

The straight part
We know that "festooned with flowers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case festooned with flowers = wreathed.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 WREATHED mean?
WREATHED verb- To place an entwined circle of flowers upon or around something.
- To wrap around something in a circle.
- To curl, writhe or spiral in the form of a wreath.
- To twist, curl or entwine something into a shape similar to a wreath.
- To form a wreathlike shape around something.
- To curl, writhe or spiral in the form of a wreath.
- To turn violently aside or around; to wrench.