Clue: Mounting a stage that is wide, making a bloomer (7)
Answer: WEIGELA
Explanation: Definition: a bloomer

[*mounting*] **<=(A **+ **LEG** ("stage") + **I.E**. (id east, so "that is") + **W** (wide, in cricket))
 

 
*Weigela is a flowering shrub with white, pink or purple flowers.