Clethra Not Blooming . They do bloom in deep shade there but grow tall and lanky. You may have pruned the tree at the wrong time (homeowners sometimes remove branches. What's Blooming? Eastern Sweet Pepperbush Wells Reserve from www.wellsreserve.org This native species, also called sweet pepperbush, flowers profusely for 4 to 6 weeks during july and august when few other plants are in bloom, and the flowers fill the garden with their spicy fragrance. If you aren’t watering your calla lilies enough or you’ve planted them in an area in your yard that doesn’t get enough natural water, they won’t bloom. Clethra alnifolia forma michauxii clethra alnifolia linnaeus, forma michauxii (courtois) zabel, in beissner et al., handb.