If you have not trimmed your azaleas yet this year, you definitely should before it’s too late! Azaleas need to be trimmed in early to mid June- At the absolute latest early July. Trimming any later can affect the blooming cycle for next year. Azaleas only bloom one time a year and if you want to enjoy their beauty next year.. Hurry before it’s too late! If you have any large or leggy azaleas, these can be trimmed back to about a third of their height. Over time, the shrub will begin to have new growth.