Beats unusual myth penned by gardeners (7)
I believe the answer is:
rhythms
'beats' is the definition.
(I know this)
'unusual myth penned by gardeners' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'myth' is 'ythm' which is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for rhythms that I've seen before include "Beats, cadences" , "Musical beats" .)