Herbaceous plants can be easily identified because they have non-woody stems. Their above-ground growth largely or totally dies back in winter in the temperate zone, but they may have underground plant parts (roots, bulbs, etc.) that survive.
What Are Herbaceous Plants?
Herbaceous plants are plants with flexible, green stems with little to zero woody parts.
Technically, all annual plants are herbaceous, because an annual is a non-woody plant. Annuals take it a step further and die altogether at the end of their lone growing season, both above the ground and below it. However, perennials can also be considered herbaceous. An example of a herbaceous stem would be a peony, which is a perennial. The tree-like banana plant, also a perennial, is known as the largest herbaceous plant.
Biennials, likewise, lack woody stems, therefore they can also be characterized as herbaceous. However, biennials such as foxglove (Digitalis) and silver dollar plant (Lunaria) maintain live, low-growing foliage above-ground during the winter (known as "basal leaves"). The question of whether a plant is herbaceous or not truly hinges on the presence or absence of woody stems, not on winter die-back.
Herbaceous Plants That Are Perennials
For Northerners, "perennials" and "herbaceous perennials" are almost synonymous. These are non-woody plants that die back to around ground level once cold temperatures return and survive the winter because of their underground plant parts. This group includes some of the most cherished plants in the landscape. The following shortlist mentions several examples of herbaceous perennial plants:
- Columbine (Aquilegia)
- Garden phlox (Phlox paniculata)
- Giant fleece flower (Persicaria polymorpha)
- Hardy mums (Chrysanthemum)
- Larkspur (Delphinium)
- Leopard plant (Ligularia)
- Mayapple (Podophyllum peltatum)
- Montauk daisies (Nipponanthemum nipponicum)
- Moon cactus (Gymnocalycium mihanovichii)
- Oriental poppies (Papaver orientale)
- Peonies (Paeonia lactiflora)
- Rodgers flower (Rodgersia)
- Society garlic (Tulbaghia violacea)
- Stonecrop (Sedum)
Even under the general classification, "herbaceous perennial," there are a number of sub-classes, based on how a plant stores nutrients underground during the winter (nutrients upon which it will draw when the weather warms up enough for it to produce vegetation once again). Everybody immediately thinks of the "roots" that survive underground during winter, but some perennials have other kinds of specialized plant parts that patiently wait out the winter below the surface.
For example, there are spring bulb plants that store nutrients in a bulb, then burst upon the scene in early springtime with a show of leaves, stems, and blooms. Daffodil flowers (Narcissus) are a well-known example. Other plants, such as dahlia flowers, differ in two ways from the spring bulbs:
- Their plant part that holds nutrients underground is classified as a "tuber," which resembles a bulb.
- Tubers are from tropical countries and they need to be overwintered indoors. They can then be brought back outdoors when warmer temperatures return; they do not bloom until summer.
Still, other herbaceous plants have "corms" to act as underground nutrition reservoirs. The enormous snake lily (Amorphophallus konjac) emerges from a corm in spring when its famously unpleasant smell begins to attract the type of bugs that feed on animal carcasses.
Even some weeds are known as herbaceous perennials. An example is Japanese knotweed (Polygonum cuspidatum), which uses underground rhizomes to store its plant food. Eradicating these persistent types of weeds typically requires more effort than getting rid of annual weeds.
Herbaceous Plants in a Northern Winter Landscape
Annuals are dead by the time winter arrives, and the basal leaves of biennials do not stand tall enough to be able to poke their heads out through the snow cover in the North. Herbaceous perennials may die back to ground level, but that does not mean that they necessarily disappear. Some turn brown and hang around (if you let them). Sometimes, their above-ground growth remains attractive, despite being dead.
If there is no evidence of disease, you can refrain from cutting down herbaceous plants until spring comes. In fact, leaving the above-ground vegetation may even afford a bit of insulation to help the plant survive winter.
Here are some herbaceous perennials you may choose not to cut back in the fall so you can take advantage of their display and offerings in the winter landscape:
- Joe-pye weed (Eupatorium; adds architectural interest)
- Coneflowers (Echinacea; wild birds eat the seeds)
- Maiden grass (Miscanthus; the straw color its leaves assume in winter is pretty)
However, remember to supplement herbaceous plants in your winter landscape design with evergreen trees and shrubs, since the latter can offer more winter interest in the landscape.