Primarily horticultural border? (5)
I believe the answer is:
hedge
'primarily horticultural border?' is the definition.
'hedge' can be an answer for 'border?' (I have seen 'Border of vegetation ' mean 'hedge' so perhaps 'border' could also mean 'hedge'). I'm not sure about the 'primarily horticultural' bit.
'primarily horticultural border?' is the wordplay.
'primarily' suggests taking the first letters.
'border?' becomes 'edge' (border is a kind of edge).
The first letter of 'horticultural' is 'h'.
'h'+'edge'='HEDGE'
Can you help me to learn more?
(Other definitions for hedge that I've seen before include "Shrubby boundary" , "appear non-committal in statement" , "sort of fund" , "Barrier of shrubs or bushes" , "Growing division" .)