Vegetables grow rapidly nursed by pantomime character (6,9)

'vegetables' is the definition.
(button mushrooms might be classed as vegetables)

'grow rapidly nursed by pantomime character' is the wordplay.
'grow rapidly' becomes 'mushroom' (I've seen this before).
'nursed by' indicates putting letters inside.
'pantomime character' becomes 'buttons' (I've seen this before).
'mushroom' going within 'buttons' is 'BUTTON MUSHROOMS'.