I have pruned sambucus nigra many times, mainly in the autumn, but can be done in the spring, either way they always seem to do well, sometimes these can get really big and in the right place can look good if left to get really large, good for sceening and creating privacy, but in a smaller area then you can be quite brutal and keep it at a manageable height. julien

If you prune it yearly you won't get flower, as it flowers on second year (and older) wood. I prune mine for the first few years, to ensure I get some strong new growth, then start making a framework of strong growth which I leave to mature and flower. Phil J