A rhizome, also known as rootstalk or more properly rootstock, is a horizontal stem of a plant from which a variety of plants can grow. These stems are known for their propensity to spread rapidly and are a frequent choice of landscapers because they can cover bare areas with lovely foliage and charming flowers over time. Not every one is grown for aesthetic purposes, however. Ginger, for example, grows from a rhizome.
Since the rhizome spreads rapidly, plants that grow from one are generally not well suited to planting in pots without replanting. The long root can easily grow too large for small pots, as in the case of bearded irises and some lilies. Gardeners, however, may want to start them in a pot and later transfer the plants to more ample space where they can proliferate.
Even when planted in an area with a great deal of space, the plant may have to be broken up after a few years, as it can become clogged, although not all require this. Ireland is known as the Emerald Isle due to its verdant proliferation of the shamrock or oxalis. Once shamrocks are planted, they do not generally need to be broken up and make wonderful fill in an empty garden space. They are tolerant of some cold weather and delight each year with dainty white blooms.
Gardeners frequently choose certain forms of rhizome because, unlike the plantings from most bulbs, they tend to have foliage year round. Certain tropical plants like orchids derive from them, and when the flowers are gone, the straight, green stalks remain to add interest to a garden.
Other flowers that can be grown from rootstock include calla lilies and cannas. Curcumas have dark pink flowers on relatively short stocks. Hedychium coccineum, once grown in the Himalayas, can grow up to 8 feet (2.44 m) tall and, when in bloom, the top eighth of the plant is composed of tiny bright orange flowers known for attracting butterflies. The butterfly ginger variety of the flower achieves the same height, but has gold to light orange blooms.
Another rhizome popular in landscaping for hedges is the bamboo, which requires virtually no attention once planted, though trimming may be necessary to affect the proper shape. Depending on the variety, bamboo can be quite tall or modestly sized, and tends to proliferate well.
The term rhizome is also used as a metaphor, to describe concepts or communities that seem to grow without any discernible mechanism. Carl Jung used the term to describe the universal unconscious, the presence of a set of shared images and their significance, that he felt existed in all people. The Internet and its rapidly spreading communities has also been described in this way because of its popularity and quick growth.