Good shower needed for corn (5)
I believe the answer is:
grain
'corn' is the definition.
(I've seen this before)
'good shower needed' is the wordplay.
'good' becomes 'g' (abbreviation).
'shower' becomes 'rain' (synonyms).
'needed' is a charade indicator (letters next to each other).
'g'+'rain'='GRAIN'
'for' acts as a link.
(Other definitions for grain that I've seen before include "Cereal seed" , "Small hard seed of corn etc" , "Character" , "Cereal crops" , "little salty bit" .)