Both varieties of lilacs are blooming. Helen hasn't bloomed in years. She was relocated in the fall (2017). Maybe that did the trick. Allen has always been a steady and reliable bloomer. Neither are ever pruned or fertilized much. Both are in the same size pot and are located close to each other. Their growing conditions are the same. Why is Helen so shy to bloom?
The Old Farmer's Almanac offers some good points for growing lilacs successfully. Maybe I should consider starting some cuttings of Helen and see if I have success. It is impossible to have too many lilacs.