Come out in the garden, mate (3)
I believe the answer is:
bud
'mate' is the definition.
(shortly for buddy)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for bud that I've seen before include "It will eventually become a leaf or flower" , "Opening flower" , "Friend" , "Tight flower" , "China to America?" .)