When is the best time of the year to trim cedar hedges? Importantly, does choosing when to trim have any affect on encouraging growth in areas recovering from small bare spots?
It is best to prune cedar hedges more than once during the growing season, starting in the spring after the sap is running. This will prevent the plant from excessive dehydration. See here. To encourage growth in the bare spots, you can try cutting out all of the dead wood in the area. Cedars do not often sprout well from old wood, but if the bare spots are mostly superficial, the plants should flush out and fill the gaps.