Potato bean, also known as hopniss, cinnamon vine, and Indian potato, is a nitrogen-fixing perennial in the Pea family that bears edible beans and large edible tubers with numerous health benefits. The vines grow quickly to 10 or more feet, and the maroon-and-cream-colored flowers shaped like pea blossoms reportedly smell of lilies. The fruits resemble a green bean measuring 2 to 5 inches long. Potato bean's native range is from Southern Canada to Florida and west to the border of Colorado. It is usually found in moist, humusy, sandy or gravelly soils in full or part sun. Provide it with its own space to grow in; this is a spreader that will grow into the roots of other plants. Some people recommend planting it alongside Jerusalem artichoke or elderberry, and others claim that the best spot for potato bean is a large container that will keep the tubers separate from everything around it. Tamara Dean's excellent article in Orion Magazine tells a highly informative story of the plant and of the scientists and foragers who have adored it, including Henry David Thoreau (https://orionmagazine.org/article/stalking-the-wild-groundnut/). The comments section is equally interesting and enlightening.
Plant tubers 2 to 3 inches deep in a moist area with at least 2 hours of sun. For best production, include sand for drainage, compost and mulch to control weed competition, and provide something for it to climb on. In its second or third year, several one-inch-thick tubers can be harvested from each plant. The tubers can be somewhat nutty, but they mostly resemble fine-textured potatoes.
Native habitats include marshes, wet thickets, stream banks and bottomland forests. Useful as a vertical accent or privacy screen. Use in containers or in edible or pollinator gardens.
Plant Characteristics:
Grows 10-16' tall.
Grows in full to part sun.
Prefers moist conditions and sandy or gravelly soils with some loam. Adapts to clay. Tolerates occasionally wet soils.
Compact racemes of five-petaled flowers arise from leaf axils June-August. Fruits are fleshy, dry pods with several seeds.
Egg-shaped, pinnately compound leaves have 5-7 leaflets up to 2 inches long. Medium green leaves have paler undersides that are occasionally hairy.
Wildlife Value:
Potato bean is a larval host plant for the silver-spotted skipper. Leafcutting bees and flies may pollinate the flowers. Mammals eat the fruits and roots.
Medicinal, Edible, and Other Uses:
The tubers are cooked and used in stews, soups, or fried like potatoes. Some current indigenous people recommend cooking the tubers for a long period of time. The tubers may be stored by boiling, peeling, and drying them, and the seeds may be cooked and eaten like peas during the summer.
The protein content of the tubers is 3 times higher than potatoes (15-30 mg/g), lacking only 2 amino acids (cysteine and methionine) from being a complete protein. A good source of omega-3 linolenic fatty acids, known for their anti-inflammatory effects. Approximately one-third of the fresh weight is carbohydrates, and the tubers are an excellent source of calcium and iron. In addition, consumption of the tubers has been shown in rat studies to lower blood pressure, cholesterol, and triglycerides, and the plant has a history of use by Native Americans for balancing hormones, due to the genistein and isoflavone content. Genistein-7-O-gentiobioside is a novel isoflavone found in potato bean that has been shown to have anti-carcinogenic function against colon, prostate, and breast cancer.
Caution: Raw tubers should not be consumed as they contain protease inhibitors that are denatured by cooking.