Plant 150 more than necessary (6)
I believe the answer is:
clover
'plant' is the definition.
(clover is a kind of plant)
'150 more than necessary' is the wordplay.
I cannot really understand how this works, but
'150' could be 'cl' (Roman numerals) and 'cl' is found in the answer.
'more' could be 'over' (I've seen this before) and 'over' is found in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for clover that I've seen before include "Three-leaved wild plant" , "Wild three-leafed plant" , "A four-leaved one is considered lucky" , "Meadow plant" , "Trifolium" .)