They share the rooting characteristics of true tubers. Depending on whom you ask, tuberous roots are either lumped in with tubers, or are a separate variety. Dahlias have tuberous roots, as do the sweet potatoes. Typically, tuberous roots have a pointed bud at the top and root more toward the bottom. The final version of bulbs is not a bulb or root at all.
Rhizomes are really thickened stems that run horizontally.
Rhizomes grow leaves and flowers from the top and, rather expectedly, roots from the bottom. Common rhizomes include the calla lilies, cannas and bearded irises. Most of us reading this newspaper reside in the third or fourth hardiness zones. It depends on the map you consult and to a lesser degree where Canada is located as you view the chart. Suffice it to say the optimum time to plant hardy bulbs is from mid-September into early October.