Lilacs, such as these at Lewis & Clark Recreation Area, are signs of spring. We notice that the order and date in which plants appear throughout the season varies some year to year. Anchor points in the growing season have been studied to help in plant management such as the grape industry. More on phenology at http://www.yankton.net/river_city/article_3f755562-ae1a-11e2-952e-001a4bcf887a.html
Plant Exchange Blog 