Sound of one planting tree (5)
I believe the answer is:
cedar
'tree' is the definition.
(cedar tree is a kind of tree)
'sound of one planting' is the wordplay.
'sound of' indicates a 'sounds like' (homophone) clue.
'one planting' becomes 'seeder' (machine that plants seeds).
'seeder' is a homophone of 'CEDAR'.
(Other definitions for cedar that I've seen before include "Great hardwood tree associated with Lebanon" , "may have needles?" , "representative of Lebanon?" , "Deodar" , "Tree (Lebanese?)" .)