On the house is a strange flowering plant (7)
I believe the answer is:
freesia
'flowering plant' is the definition.
(type of flower)
'on the house is a strange' is the wordplay.
'on the house' becomes 'free' (something on the house is given away free).
'strange' is an anagram indicator.
'is'+'a'='isa'
'isa' with letters rearranged gives 'sia'.
'free'+'sia'='FREESIA'
(Other definitions for freesia that I've seen before include "Fragrant-flowered plant; faeries (anag.)" , "bloomer" , "See fair for fragrant flowers" , "Highly scented flower" , "Scented South African plant" .)