Northern Catalpa (Catalpa speciosa): A Complete Guide No these aren't giant tree green beans, but instead the seed pod of the northern catalpa. These bean like pods can grow to be 20" long and contain numerous 1" long seeds. #haverfordcollegearboretum # No these aren't giant tree green beans, but instead the seed pod of the northern catalpa. These bean like pods can grow to be 20" long and contain numerous 1" long seeds. #haverfordcollegearboretum # While catalpa trees are not generally considered highly toxic, some parts of the tree, particularly the roots, are known to be poisonous according to the USDA Plants Database. The leaves and seed best 10+ vape tricks for Beginners