At home, its contents may well be growing (7)
I believe the answer is:
planter
'at' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for planter that I've seen before include "Sowing machine" , "Settler or colonizer" , "Decorative pot" .)