Park-keeper visiting old Yankee where fruit-trees grow (8)
I believe the answer is:
orangery
'where fruit-trees grow' is the definition.
'park-keeper visiting old yankee' is the wordplay.
'park keeper' becomes 'ranger' (I've seen this before).
'visiting' means one lot of letters goes inside another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'yankee' becomes 'y' (phonetic alphabet: alpha, bravo, charlie etc.).
'o'+'y'='oy'
'ranger' going into 'oy' is 'ORANGERY'.
(Other definitions for orangery that I've seen before include "Building for citrus growing" , "glasshouse" , "fruit source" , "fruit is grown here" , "Place for growing fruit in cool climates" .)