Check with your local garden center but something like sulfur.
For major pruning, the best time is in early spring before the plant is ready to put out new growth, so it has the full growing season to fill out and for the new growth to mature.
When pruning azaleas to reduce height, particularly older plants, it is best to do the pruning in stages, to minimize the shock to the shrubfall.clubted Reading Time: 2 mins. Ensure a riot of flowers to enjoy next summer and put up your clippers after springtime. The ideal time to give your azaleas a trim is within a three-week period after they finish blooming in spring. This gives the azaleas plenty of time to make flower buds (which appear as pale, fuzzy buds curled tight on the tips of branches) for next shrubfall.clubted Reading Time: 2 mins.
You want to prune as soon after blooming as possible, and before the plants put on the flower buds for next year’s blooms. If you are trying to schedule azalea pruning on your calendar, prune in April.
If you cannot prune in April then do it in May. If you wait past May you will probably not get flowers next shrubfall.clubted Reading Time: 7 mins. Renew overgrown plants by cutting them back to within 6 to 12 inches of ground level. This practice results in abundant new growth by midsummer.
The best time to renew azaleas is before spring growth begins. This allows sufficient time for next year’s flower buds to form in midsummer, and for new growth to mature and harden off for winter. Dec 17, Rejuvenating pruning is done in winter and maintenance pruning in early spring, but there are times of the year when an azalea should not be pruned. Pruning after midsummer is. Jun 24, Immediately after blooming is the best time to cut back or trim azaleas.
Cutting back right after blooming gives the gardener a chance to get the dead blooms off of the plant and to shape up the shrub. If you wait and prune the azalea later in the year, there’s a chance that you could prune off next year’s blooms.