Plant one on each side (5)
I believe the answer is:
onion
'plant one' is the definition.
The definition and answer can be both plants as well as being singular nouns.
Maybe there's a link between them I don't understand?
'on each side' is the wordplay.
'on' says to put letters next to each other.
'each' becomes 'oni' (I am not sure about this - if you are sure you should believe this answer much more).
'side' becomes 'on' (I've seen this in other clues).
'oni' put next to 'on' is 'ONION'.
Can you help me to learn more?
(Other definitions for onion that I've seen before include "Bulb used in cooking" , "Aromatic flavourful versatile vegetable" , "Tear-jerking bulb" , "Tear-inducing edible bulb" , "Bulb used as a vegetable" .)