In South Africa I grow supportive of the national drink? (6)
I believe the answer is:
protea
'in south africa i grow' is the definition.
(genus of South African plants)
'supportive of the national drink?' is the wordplay.
'supportive of' becomes 'pro' (as in being pro a person or cause).
'the national drink?' becomes 'tea' (iconic drink of England).
'pro'+'tea'='PROTEA'
(Other definitions for protea that I've seen before include "S. African shrub; to pear (anag.)" , "South African plant" , "Ascend" , "South African evergreen" , "South African shrub" .)