In April and May, the heady perfume of blooming lilacs fills the air and lures visitors to the Louisa Clark Spencer Lilac Collection, just northeast of the Cranford Rose Garden. The collection features 150 specimens of these much-loved shrubs, including over 20 of the known lilac species and subspecies, and 130 cultivars. Their fragrant flowers range in seven colors: white, violet, bluish, lilac, pinkish, magenta, and purple as well as bi-color “sensations”, and they come in single and double forms.
Early lilacs, such as Syringa x hyacinthiflora 'Annabel', begin blooming in late April. Soon after, around the first week in May and peaking on Mother's Day, come the flowers of the common lilac, S. vulgaris. By Memorial Day, late-blooming lilacs such as S. reflexa, S. villosa, and S. x prestoniae are at their peak. The last to bloom, in the second week in June, are the spicy-scented tree lilacs S. reticulata and S. pekinensis, both with single white flowers and attractive cherrylike bark.
When Dr. C. Stuart Gager, BBG's first director, noted in the annual report for 1917 that World War I was "disrupting the Garden's acquisition of choice varieties," the collection already included more than 100 varieties of common lilac (Syringa vulgaris). Clearly, the wartime interruption was only temporary as the collection continued to grow. In 1981 and 1982 the collection underwent a major reorganization to highlight the plant’s contrasting color and species varieties. Today, the collection is called The Louisa Clark Spencer Lilac Collection in honor of the chairman of the board of the garden from 1977–1982.