One may strain to improve it (3)
I believe the answer is:
tea
'one may' is the definition.
The definition and answer can be both plants as well as being singular nouns.
Maybe you can see a link between them that I don't see?
'strain to improve it' is the wordplay.
I cannot quite understand how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is present in the answer.
The remaining letters 'ea' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for tea that I've seen before include "Cha" , "Evening meal - eat up" , "Plantation product" , "Refresher course" , "Infused beverage" .)