Special gear enthusiast brought to plant, having crossed yard (5,5)
I believe the answer is:
fancy dress
'special gear' is the definition.
'enthusiast brought to plant having crossed yard' is the wordplay.
'enthusiast' becomes 'fan' (fan is a kind of enthusiast).
'brought to' means one lot of letters go next to another.
'plant' becomes 'cress' (**).
'having crossed' is an insertion indicator.
'yard' becomes 'yd'.
'cress' placed around 'yd' is 'cydress'.
'fan'+'cydress'='FANCY DRESS'
(Other definitions for fancy dress that I've seen before include "Party costume" , "Themed party attire" , "Masquerade costume?" , "Frivolous party garb" .)