Just the plant to border part of the canal (7)
I believe the answer is:
hemlock
'just the plant' is the definition.
I can't judge whether this definition defines the answer.
'border part of the canal' is the wordplay.
'border' becomes 'hem' (I've seen this before).
'part of the canal' becomes 'lock' ('lock' is part of 'canal').
'hem'+'lock'='HEMLOCK'
'to' is the link.
Can you help me to learn more?
(Other definitions for hemlock that I've seen before include "Poisonous drug" , "Poison killing Socrates" , "Highly poisonous relative of parsley" , "Poisonous weed" , "Socratic poison" .)