Unorthodox types of bonsai spreading across border (9)
I believe the answer is:
bohemians
'unorthodox types' is the definition.
(unorthodox or eccentric people)
'bonsai spreading across border' is the wordplay.
'spreading' indicates anagramming the letters.
'across' means one lot of letters goes inside another.
'border' becomes 'hem' (I've seen this before).
'bonsai' with letters rearranged gives 'boians'.
'boians' enclosing 'hem' is 'BOHEMIANS'.
'of' acts as a link.
(Other definitions for bohemians that I've seen before include "Some Czechs" , "Unconventional people" .)