Last year, following Great Uncle Hamish’s principles (or rather, not following them), I hacked back an overgrown philadelphus, as described in this post. Recently I took up the secateurs again to do a bit more work on the same bush. Once you start pruning philadelphus, it is as well to continue from year to year, or else your good work goes for nothing as new shoots rapidly fill in the gaps you have made. Since it is yet another garden task to add to the list, it may be as well to leave your shrub alone unless it has outgrown its welcome or is looking constipated. But if you are going to prune it, soon after it has finished flowering is a good time to do it.
I started by cutting out weak new shoots from the middle of the bush, to make room for light and air to get in. Pruning usually has the effect of stimulating the shrub to produce new shoots from the base of the plant, and it is as well to leave these unless they are going to get in the way.
Some of the old wood I had shortened last summer had only produced feeble new growth. These I cut right back, being careful not to destroy any good growth higher up as I pulled the branches out.
There is plenty of new growth coming away from the wood I cut back last year. This will flower over the next two years.