Answer: There's really no explanation for the branches to fail to produce flowers. Flowers form on the previous year's growth rather than new growth, so prune as soon as the flowers have faded. Pruning encourages lots of new growth, which should flower next winter. As your plant matures, you can cut back about a third of the stems that are more than four years old to within four inches of the ground. Best wishes with your forsythia!
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