The most common and most likely answer to this crossword clue is the 7 letter word CAPABLY
C
A
P
A
B
L
Y
Buddy explains!
The straight part
We know that "How Lancelot Brown landscaped his gardens?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case how lancelot brown landscaped his gardens? = capably.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 CAPABLY mean?
CAPABLY adverb- In a capable manner.