Right after daffodils, tulips and hyacinths have spent their last flowers, many homeowners mow the plants down. That’s a bad idea if you want them to keep flowering year after year. Spring-flowering bulbs need to photosynthesize and produce food in order for the bulbs to enlarge and set the stage for the following year. For that, leaves are needed. “The plants are collecting the groceries for next year’s flower,” said David Trinklein, horticulture specialist for University of Missouri Extension. “The longer we can encourage spring-flowering bulbs to photosynthesize, the better the flowering performance will be next year.” Some homeowners don’t mow them down but tie them up into little columns. “You might as well cut them off because only the outer leaves will get sun and the light will be at a very poor angle. Therefore, photosynthesis will be minimal, at best,” Trinklein said. The foliage of springflowering bulbs eventually will turn yellow and die back naturally, he said. These…