At this time it is not yet necessary to clip the Box (buxus) topiary as such. However to maintain a way through the herb-garden, we do a partial clipping of these buxes. That is that for now, we only clip the edges on the sides where the pathway goes through. Yes, you may call me a lazy gardener. I call it pragmatic.
Usually we clip these plants to keep the shape. This should be done before there is too much growth as it will be harder to reshape the plant.
Clipping should be done in the growing season, from May and no later than the end of August. Part of the problem we saw this season could very well have been caused by a last clipping end of September.