Mixed up marl I needed for plant (7)
I believe the answer is:
primula
'for plant' is the definition.
(primula is a kind of plant)
'mixed up marl i' is the wordplay.
'mixed' is an anagram indicator.
'up'+'marl'+'i'='upmarli'
'upmarli' with letters rearranged gives 'PRIMULA'.
'needed' is the link.
(Other definitions for primula that I've seen before include "Plant such as cowslip" , "Cowslip, perhaps" , "Spring flower" , "Cowslip genus" , "Polyanthus" .)