Rhizomes are modified stems running underground horizontally. They strike new roots out of their nodes, down into the soil. They also shoot new stems up to the surface out of their nodes. This rhizome activity represents a form of plant reproduction. These underground plant parts also store nutrients.
The thuggish nature of much of the vegetation you will find on invasive plants lists, including Oriental bittersweet (Celastrus orbiculatus), is due to the vigor of the rhizomes of these aggressive plants. One reason why it is so difficult to eradicate an invasive plant that uses rhizomes to multiply is that, from a piece of rhizome left behind in the soil (after you have tried to dig the plant out, for instance), a new plant can emerge. Examples of aggressive weeds and/or invasive plants that spread out of control with the help of rhizomes include:
Thuggish Landscape Plants That Spread via Rhizomes
But it is not just totally undesirable plants that can spread via rhizomes. Some of the attractive plants that we use in landscaping share this quality with unattractive, weedy plants.
For example, despite their pretty little bell-shaped flowers, which are quite aromatic, many gardeners consider lily-of-the-valley plants (Convallaria majalis) problematic due to their invasive rhizomes. Golden hops vine (Humulus Summer Shandy) is another specimen whose beauty is marred by vigorous rhizomes that make the plant an ill-behaved member of its gardening community. There are numerous other examples, such as:
- Black bamboo (Phyllostachys nigra)
- Bugleweed (Ajuga reptans)
- Bunchberry (Cornus canadensis)
- Chinese lanterns (Physalis alkekengi)
- Border grass (Liriope spicata)
- Heavenly bamboo (Nandina domestica)
- Interrupted fern (Osmunda claytoniana)
- Papyrus (Cyparus papyrus)
- Plume poppy (Macleaya cordata)
- Tansy (Tanacetum vulgare)
- Wall germander (Teucrium chamaedrys)
- Virginia creeper (Parthenocissus quinquefolia)
- Yellow archangel (Lamium galeobdolon)
In each case, you will have to decide for yourself whether the beauty of a plant that spreads by rhizomes offsets its tendency to become a nuisance. Some gardeners put up with the invasive quality of bugleweed because they admire its pretty flowers or foliage, but others regard it as one of the worst plants to grow in the yard.
In the end, it may come down to how much control you need to have over exactly what is growing across each square foot of your property. If you are the type who can't stand to see a weed growing anywhere on the lawn, then you should avoid growing plants with rhizomes at all costs.
If you see "creeping" in a plant's common name or reptans or radicans in its Latin name, that is often a good indication that the plant uses rhizomes to store nutrients and to multiply without the use of seeds. It is also a possible red flag for gardeners who value low-maintenance landscaping and do not want to be saddled with rhizomatous plants that will be constantly popping up in spots where they are not wanted.
However, rhizomes are not always a bad thing. There are some well-behaved plants that have rhizomes, such as Tropicanna canna lilies (Canna Phasion). Some plants with rhizomes, such as German iris (Iris germanica), are so valued in the landscape that gardeners generally want them to multiply.
Also, sometimes you grow a plant specifically so that it will spread and fill in bare spots in problem areas where other plants will not grow well. A plant has to be tough to serve this purpose. So, while its ability to spread is regarded as thuggish in certain instances, that same ability may be a godsend in others.
The very name, "ground cover," is often used with the implied meaning that such a plant will spread out over a large area, thereby suppressing weed growth or fighting erosion on a slope. The rhizomes of the popular ground cover Pachysandra terminalis allow the plant to do just that.
Rhizomes vs. Roots, Stolons
Rhizomes and stolons (for example, grass stolons) are similar plant parts but distinguished from each other by the fact that stolons remain above-ground, while rhizomes do their spreading underground.
To distinguish rhizomes from roots, remember that rhizomes, unlike roots, are modified stems. As such, they bear nodes, from which brand-new plants can spring.