Jack Alexander, Plant Propagator for the Arnold Arboretum, presents a single session class at the Dana Greenhouses in Jamaica Plain on Saturday, March 13, from 9 am – 1 pm.  There’s nothing more satisfying to a gardener than growing plants from seeds. From annuals and perennials to trees and shrubs, success can be achieved if you understand what triggers germination. Expert propagator Jack Alexander will share techniques and tips for starting various types of plants from seeds. This workshop is for beginners and those who have been frustrated in past attempts to transform seed to seedling. Students will leave class with a selection of seeds raring to grow. Aftercare will be necessary. Fee $45 Arnold Arboretum member, $55 nonmember. To register, log on to www.arboretum.harvard.edu.