Pruning in March
If a periwinkle needs pruning, the best time to do this is in March. The greater and the lesser periwinkle can be treated in the same way, also with regard to pruning.
Plants and shrubs that grow very fast can become so large that they no longer fit in the space originally intended for them. Fortunately these plants can generally be pruned fairly drastically to keep them under control, and they will soon produce new shoots. It may be a good idea to trim regularly from them on to keep them in shape.
Cut back to just above the ground, although you should not take this too literally, as there must be enough of the plant left for it to regrow. To determine the pruning height, make sure you do not cut beyond where the plant begins to branch. This section must be left undisturbed. The more branches are retained, the bushier the shrub will be as it grows back. Leave some length on these branches, as the new growth will come from the dormant buds.