Hello Gardeners, I’m Amanda McNulty with Clemson Extension and Making It Grow . Elderberry stems are semi-woody, the interior is filled with pith. The late John Fairey, renowned botany professor at Clemson, told his students that this pith was collected and used to pack delicate scientific instruments and by repairmen to hold tiny parts of watches, back in the day when people actually fixed mechanically-run timepieces. Mason bees and other insects, however, have long used them as places