With gorgeous hydrangea cultivars flooding nurseries and garden centers, it can be challenging to choose just one (or a few!). Magnificent blooms in rich colors entice, yet their allure can lead you to purchase hydrangeas that will not thrive in your garden. Don’t let this happen. Instead, join Jen Kettell at the Arnold Arboretum of Harvard University on April 19 at 6 pm for a lively discussion on the species behind the hot trade names—especially their inherent growth characteristics—and learn how to match appropriate plants to your site conditions. She’ll suggest which species are drought-tolerant or benefit pollinators and demonstrate pruning to maximize flowering and other essential growing tips. Jen will focus on hydrangeas that are hardy in Zones 5-7. Class includes an indoor lecture and walk to a demonstration in the Leventritt Shrub and Vine Garden. Fee $25 Arboretum member, $35 nonmember. Register at http://my.arboretum.harvard.edu or call 617-384-5209.  Image from http://www.whiteflowerfarm.com.