The most common and most likely answer to this crossword clue is the 6 letter word SEEDER
I've seen this crossword clue in Financial Times
S
E
E
D
E
R
Buddy explains!

The straight part
We know that "garden tool" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case garden tool = seeder.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 SEEDER mean?
SEEDER noun- A device used to plant seeds; a seed drill
- An implement used to remove the seeds from fruit etc.
- A person who seeds clouds in order to make it rain
- (file sharing) A person connected to a peer-to-peer network who has a complete or partial copy of a given file and makes it available for downloading.
- A process that seeds a random number generator.