First, let's define what kind of lilac. East Coast tree-type lilac. Not ceanothus -- prevelant & practical for Native American soap making. No full-fragrant & purple in nature.
So, what's the connection between lilac and poetry? Purple passages. A full fragrance which isn't cloying and evokes the finest of memories.
Where in San Francisco? The Arboretum, of course. Across from the native California section. Go quickly -- she's in bloom. Wander through thenative California section and take in the tightly curcled ceanothus bushes. Enjoy a fully purple day.