A number of evergreens in dry surroundings, initially (2,5)
I believe the answer is:
at first
'initially' is the definition.
(synonyms)
'a number of evergreens in dry surroundings' is the wordplay.
'number of evergreens' becomes 'firs' (fir is an evergreen tree).
'in dry' becomes 'tt' (abbreviation for teetotal. I am not sure about the 'in' bit.).
'surroundings' means one lot of letters goes inside another.
'firs' placed within 'tt' is 'tfirst'.
'a'+'tfirst'='AT FIRST'
(Other definitions for at first that I've seen before include "To begin with" , "In the beginning, to start with" , "Originally" , "In the beginning, initially" .)