euphorbia characias black pearl

somerset steve

Morning everyone! I love my euphorbias but the black pearl has some stems where the leaves are turning yellow and falling off and other stems which are not affected. Is this just part of its natural growth process or is there something wrong? All the gorgeous flower heads are in a good state its just the leaves starting to drop from the lowest foliage of some stems upwards. I'm wondering if some of the stems should have been cut off to give the plant a refresh? I know it can get to several feet in some cases and am eager to keep it under control.