Growing source of a bit of a smell, possibly? (4)
I believe the answer is:
elms
If this is the answer, I'm afraid I cannot explain it.
Can you help me to learn more?
(Other definitions for elms that I've seen before include "Deciduous trees with rough serrated leaves" , "Trees (of late, prone to disease)" , "Trees sound like Cockney steering devices" , "rugged feature of country churchyard" , "may have many leaves" .)