They're used to water certain flowers (5)
I believe the answer is:
roses
'flowers' is the definition.
(rose is a type of flower)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for roses that I've seen before include "Occupants of bed" , "Beautiful flowers, seen annually in Tralee" , "Fragrant flowers" , "chocolates" , "Flowers for watering cans?" .)