Bulbs are among the most interesting, most beautiful and easiest to grow of all flower varieties. Tulip bulbs were once so prized in Holland that it led to one of the best known financial bubbles in history, and even today, tulips are a leading export from that part of the world.
Even though bulbs are not quite so highly prized today as they were in 17th century Holland, they are still loved for their scents, their colors and their shapes, and gardeners love the fact that most bulbs are hardy and easy to grow.
Many of the most popular varieties of flowers are actually grown from bulbs, including tulips, crocuses, daffodils, irises, lilies, daylilies, dahlias and snowdrops.
One thing all bulb based plants have in common is that they grow from structures located under the ground. These underground structures provide the nutrients and energy the plants need to grow.
Even though bulb based plants are collectively known as “bulbs’, there are actually five distinct types of bulb plants – the true bulb, the corm, the tuber, the rhizome and the tuberous root. This article will provide examples of each type.
The True Bulb
The true bulb is in reality an underground stem base containing an embryonic plant. The embryonic plant contained within the steam base already contains the leaves, stems and flower buds, all ready to burst forth once optimal growing conditions are provided. This setup allows the plant to lie dormant during adverse conditions, and thus to survive droughts and other environmental challenges.
The embryonic plant contained within the stem base is surrounded by scales (modified leaves that overlap in a manner reminiscent of reptile or fish scales). At the bottom of the bulb is a basal plate; this basal plate holds the scales together and produces the roots of the plant.
Examples of true bulbs are such popular flower varieties as daffodils, tulips and lilies. True bulb varieties of plants are susceptible to dryness and must be handled carefully. When properly cared for, however, individual bulbs can live for many years without being planted.
A corm, like a true bulb, also contains a stem base, but the tissue of the base is solid, and it lacks the scales seen in true bulbs. The roots grow from a basal plate which is located at the bottom of the corm, and the growth point is located at the top of the corm.
Popular types of corms include gladiolas and crocus. Each corm lasts for a single season, and as the corm shrinks away after blooming, a new corm forms on top of it. In addition, small increases, called cormels, are produced around the base of the corm’s basal plate.
Like corm and true bulbs, a tuber is actually an underground stem base. Unlike corms and a true bulbs, however, the tuber does not contain a basal plate. Instead, the roots of the tuber grow from both the base and from the sides. A tuber will have multiple growth points spread out over its top surface.
The rhizome is actually a thickened stem that grows either partly or completely underneath the ground. The largest growth point on a rhizome is located at one end, and additional growth points are located along the sides. The most well known rhizome is the bearded iris.
Unlike other types of bulbs, which are actually specially adapted stems, the tuberous root is not a true root. Instead, fibrous roots designed to absorb nutrients and water grow from the sides and the tip of the tuberous root. Most tuberous roots grow in a cluster, and swollen tuberous parts radiate out from a centralized point. The growth points of a tuberous root are found on the bases of the old stems and not on the roots themselves. Dahlias and daylilies are the best known examples of tuberous roots.