Dedicated volunteers have been tracking the phenology of cloned and common lilacs since the 1950s. The observations have been invaluable in documenting plant responses to changing spring conditions. This information has been used along with historical weather data across the country to capture the timing of Spring Indices, such as leaf-out and flowering that primarily vary with temperature.

At the Gardens we are monitoring 29 individual Syringa vulgaris, the common lilac, including 25 S. vulgaris varieties. Monitoring all of the varieties in one location provides the opportunity to determine how phenology varies among the varieties.

In 2013 we also planted two cloned lilacs (Syringa x chinensis 'Red Rothomagnesis') which we received from the USA National Phenology Network (USA-NPN). Data collected from these and other cloned lilacs allow phenological comparisons across the country without genetic variation contributing to differences in timing.