rhizome [ rahy-zohm ] noun: a modified plant stem growing horizontally at or just below the surface that sends out roots and shoots from its nodes
Those of us who garden are probably most familiar with a rhizome as one of those brown knobby things irises grow out of. The mind of a cook might turn to ginger, which my neighbor thought this gardener was offering him when she recently thinned her irises. Irises are an example of a plant that thrives best if its rhizome is close to the surface with the top part exposed. True roots absorb nutrients from the soil and do not have nodes. Rhizomes store some nutrients that then fuel the growth of roots and shoots.
Another example of a rhizomatous plant is Polygonatum odoratum ‘Variegatum’ (fragrant Solomon’s seal), which spreads and multiplies happily a couple of inches under the soil. But not all rhizomes are chubby in the way of irises and Solomon’s seals. Some, such as bermudagrass, are more fibrous. It, like many rhizomatous plants, has a “thuggish nature” according to a University of Arkansas source. Bamboo is another one that has invaded many a yard. In fact, some of the world’s most noxious agricultural weeds–purple and yellow nutsedges–sprout from tubers that form along creeping rhizomes. Most ferns also grow from rhizomes. Those with vertical rhizomes form rosette-like clumps, but those with creeping rhizomes form frond clusters scattered along the stem and can spread easily in the right environment forming complex underground networks. To prevent future problems, understand how a plant spreads before placing it in the ground.
Rhizomatous spread is a desirable feature in many turf grasses, according to the University of Minnesota, and can be useful in the cultivation of cool weather lawns. That spreading tendency can also be useful in other settings. Panicum virgatum (switchgrass), for example, is recommended as a native ornamental grass in MGNV’s Tried and True Native Plant Selections for the Mid-Atlantic Region. But beyond its beauty, consider that from its rhizomes, it puts out strong, deep (up to 10 feet) root systems that are critical in erosion control.