A common question is when is the best time to prune Cercis. The answer really depends on what is wanting to be achieved. If a large plant requires heavy pruning to re-shape then to prune heavily in late winter is usually the best. The new growth comes away very vigorously in the spring and no damage is likely to occur. Of course by doing this, much of the flowering wood is probably going to be removed so reducing the flower display for that spring. To avoid this, the pruning can take place after flowering, but then the new growth will be later and too soft to give flowers the following spring, so either way pruning reduces flowering in the near future.
If pruning Cercis Forest Pansy, as it gives so few flowers anyway, it’s not a loss and late winter pruning can be an excellent way to give a new vigour to older plants and an improved shape.
For light regular pruning it is best to leave until early spring, just before the flowers and leaves open. There is often a little die-back with Cercis grown in cooler climates like the UK (especially following a cool wet summer like 2012) and if pruning is delayed until this period then any die back can be removed at the same time.
Whatever you choose we would suggest not pruning from mid-summer until late winter unless absolutely necessary.
Use sharp secateurs to make a clean cut,just above an outward facing bud.
Good luck and enjoy your Cercis.