Weed producing trickle! (4)
I believe the answer is:
drip
I believe this is a double definition.
'weed' is the first definition.
(thesaurus)
'trickle' is the second definition.
('drip' can be a synonym of 'trickle')
'producing' is the link.
(Other definitions for drip that I've seen before include "Small drop; ineffectual person" , "Weak and pathetic person" , "Hospital equipment; weak person" , "Ineffectual type" , "Weed - seep" .)