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| Pixabay: Anemones |
Bulb is defined as any plant that stores its complete life cycle in an underground storage structure. The primary purpose and function of bulbs is to store nutrient reserves to ensure the plants’ survival. Bulbs are usually perennials. They have a time for growing and flowering that is followed by a period of dormancy when they will die back to ground level at the end of the growing season.
There are five types of bulb storage structures: true bulbs, corms, tubers, tuberous roots and rhizomes. Fleshy roots can be added as another category for the purpose of showing the structures found in daylilies and peonies.
True Bulbs
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| Courtesy University of Illinois |
True Bulbs have five major parts and are often described as tunicate or non-tunicate based on their structure.
A tunicate bulb has a paper-like covering that protects it from drying and injury. Some examples include tulips, daffodils, hyacinths, onions and garlic. A non-tunicate bulb does not have the papery outer coating. Instead, it has outer scales that are succulent and separate, giving the bulb a scaly appearance. An example is lily.
Many plants such as daffodils form new bulbs around the original bulb. These bulbs, called offsets, develop from buds within the base of the mother bulb and produce new plants. When these bulbs become overcrowded, the flowers start to diminish in size. This is an indication that it is time to dig up and divide the bulbs in the Fall.
Corms
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| Courtesy University of Illinois |
A corm is a short, vertical, swollen underground plant stem that serves as a storage organ that some plants use to survive winter. Corms do not have visible storage rings when cut in half –and, this distinguishes it from a true bulb. Examples are gladiolus and crocus. When gladiolus corms are dug in the Fall, they should be separated into well-developed corms for storage until replanting in the Spring.
Tubers
Tubers differ from true bulbs and corms by not having a basal plant from which the roots develop nor a protective tunic covering. The roots store the nutrient reserves. Examples of plants that develop from tubers include caladiums, oxalis, anemones, and the potato.
Tuberous Roots
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| Courtesy University of Illinois |
The nutrient reserves are stored in the actual root instead of an enlarged stem.
An example would be dahlias. The dahlia reproduces from buds at the top end of the root or base of the stem. The tuberous root of a dahlia should not be divided before placing in storage in the fall. It should be divided into sections with an eye bearing portion of the stem left with each section at planting time in the Spring.
The tuberous-rooted begonia reproduces from buds on top of the round, flat tuber.
Rhizomes
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| Courtesy University of South Florida |
A rhizome is a modified, underground stem that is unique in that it grows horizontally through the soil. Examples include iris, canna, ginger, and bamboo. This type of rooting structure can be invasive on some plants. These should be divided in the Fall.
Fleshy Roots
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| Courtesy Pure Peonies |
They are enlarged, fleshy root tissue that acts as the primary storage tissue for nutrients. They lack nodes and internodes, and buds are present only at the crown or stem end of the root. Examples are peony and daylily. Both peonies and daylilies can be propagated by dividing. The root clumps of peonies should be divided in the fall leaving at least three crown buds with each clump.