Weigela require pruning to control their size. This isn't necessary of all weigela shrubs--only those you desire to keep a uniform appearance. Being that weigela is a flowering shrub, however, you must use care not to prune away the buds that produce next year's flowers. Pruning before the spring bloom removes any prospective blooms, but waiting too late in the fall means the buds have already formed. Timing is more important than technique if you want to keep your weigela shrubs attractive and flowering.
Inspect the plant in early spring before the flowers open. Prune off all dead and broken branches that didn't survive winter. Use sharp pruning shears. Trim right above the location of the leaf bud to encourage lateral branching.
Wait until the shrub stops producing new flowers before pruning it back. Avoid waiting much longer than that, as new buds begin appearing in late summer.
Trim back each branch no more than one-third of its length. Cut each branch at a 45-degree angle with your pruning shears, making sure to leave some live leaves on each branch.
Thin out areas that have become too dense. Cut off branches in the cluster with the least amount of leaves all the way to the main stem.
Complete pruning by shaping the plant evenly. Trim the outer branches to similar lengths to give the weigela a full, symmetrical appearance.