It's of growing potential (4)
I believe the answer is:
corm
'potential' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for corm that I've seen before include "Underground part of iris, crocus, etc" , "Underground feature of crocus, gladiolus etc." , "Underground bulb-shaped stem" , "should eventually flower" , "Underground part of, eg, cyclamen" .)