Precious stone dug up in part of summertime garden (3)
I believe the answer is:
gem
'precious stone' is the definition.
(gem is a kind of precious stone)
'up in part of summertime garden' is the wordplay.
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'in part of' indicates a hidden word (I've seen 'in part' mean this).
'meg' can be found hidden inside 'summertime garden'.
'meg' back-to-front is 'GEM'.
'dug' is the link.
I am not very happy about this link. It may be part of another bit of the clue.
(Other definitions for gem that I've seen before include "Pleasant and cheerful (from German)" , "Half of 7 [SIGN OF THE ZODIAC]" , "Valued person; jewel" , "A jewel of an Orangeman" , "Emerald or sapphire, say" .)