Pruning or deadheading the spent blossoms of weigela is not necessary to make it rebloom. It will continue to flower in waves all season long even if you never prune it. However, if you’re like a lot of people, you just can’t resist the urge to prune your shrubs. If that describes you, then head out with your hedge trimmers or clippers to prune your Sonic Bloom weigela right after it is finished blooming in spring. Trim it into the shape you desire, taking care not to remove more than 1/3 of the total plant.
Traditional weigelas set their flower buds on “old wood”, meaning last year’s branches. That means if you prune them in the fall, you’ll risk cutting off next spring’s flowers. Modern Sonic Bloom varieties carry an “insurance policy” in the form of summer flowers that bloom on “new wood”, meaning the new growth. So, even if you forget and prune them in the fall, you’ll still see the second round of flowers that start in midsummer and continue to frost.
In early spring, scratch some slow release plant food formulated for trees and shrubs into the soil around your weigelas. That will help them get off to a strong start.