American groundnut (Apios americana) is the North American equivalent to the South American potato. Unlike common potatoes, American groundnut is a perennial flowering vine which produces numerous tubers along its root system. The entire plant is edible though the tubers are highly valued by foragers and wild food enthusiasts for their nutty, slightly sweet flavor.
American groundnut plants grow wild from Eastern Canada down to Florida and as far west as Colorado. The plant has a long history with Indigenous communities who call it by various common names including potato bean, vine potato, and hopniss.
Benefits of American Groundnut
American groundnuts are part of the legume family (Fabaceae), so their roots form a symbiotic relationship with nitrogen-fixing soil microbes. As a result, the tubers have roughly three times the amount of protein as common potatoes and “fertilize” the soil over time. The tubers also contain significant amounts of healthy fatty acids, iron, and calcium.
Despite hopniss’ nutritional value and its status as a staple crop to Indigenous communities and early settlers, American groundnut has been pretty much neglected and isn’t cultivated outside of niche permaculture communities.
Interestingly, the only place where American groundnuts is farmed for commercial purposes is Japan. They are similar to an East Asian plant called hodoimo (Apios fortunei). No one really knows how or why American groundnuts were brought over to Japan, but it has become popular in some areas for its reported health benefits.
How to Grow American Groundnut
They can’t be found in the grocery store and it can be difficult to find seeds or tubers at conventional plant retailers. Some native plant sellers sell tubers which can be planted in the fall so plants start growing in spring. There are ‘improved’ varieties with larger tubers being sold online, which are remnants from research during the 1980s at Louisiana State University (LSU). Plants can also be started by planting beans in springtime.
You might be able to ask a local forager or permaculturist if they have any plants or know where to find them in the wild for a source or tubers or seeds.
If you can find a wild plant you can gently dig up the string of tubers and separate each one. Try not to pull on the underground woody vine as it’s brittle and you’ll lose track of the tubers if it snaps.
To plant the tubers, simply place them about 2 inches (5 centimeters) deep and water deeply. They need to be close to the soil surface to sprout and should be about two feet apart. After about two weeks the tubers will produce a shoot and will need a structure to climb on, similar to peas. They are hardy in zones 4 to 9.
Hopniss prefers moist, well-drained rich soil. They’re not particular about soil pH and can grow in full sun or part shade. The plants prefer to be consistently moist so it’s best to use a few inches of mulch to prevent the soil from drying out.
After they establish, the plant needs very little care. American groundnut vines grow quickly in ideal conditions, reaching heights of over ten feet before the plant dies back to the ground before winter. They can grow over other plants or trees and spread around the garden if left to their own devices, so it’s best to grow them over a structure and give them their own space. The vines produce showy pinkish brown or purple flowers which add spring interest and attract native pollinators.
How to Harvest American Groundnut
The tubers can theoretically be harvested at any time, though it’s recommended to wait two years after planting so that the tubers are large enough to peel. The longer the tubers are kept in the soil, the larger they get, and some say they get stringy or woody when they’re left in the ground for over three years. To harvest, find the base of the vine and dig around it to find the string of tubers. Small tubers can be left in the soil for next year’s harvest.
The best time to harvest is in the fall after the first frost. When the weather cools, the plants will die back and move the sugars from their leaves and stems into the tubers, making them taste sweeter. You can also leave tubers in the ground and harvest them in the spring after the ground thaws but before they produce new leaves.
The beans can be harvested like peas in the summer and fall.
How to Eat American Groundnut
As mentioned previously, American groundnut is a type of legume, and legumes contain anti-nutrients that need to be degraded through soaking or cooking. The plant isn’t toxic, but for best results you should only consume the cooked tubers and beans. Many people have tried to eat raw tubers and were rewarded with stomach problems.
Another issue to consider is the skin – unlike the skin of a potato, groundnut skins are thicker and rougher, and contain latex. So, the skins should be peeled off before cooking for the best texture and flavor.
The peeled tubers can be boiled, mashed, roasted, fried – you can try them in any recipe that calls for potatoes, including potato-based dips like skordalia. Hopniss tends to be denser than common potatoes so cooking times are slightly longer (about 30 minutes, or until you can stick a fork through). They should be eaten warm for the best consistency.
Hopniss tubers can also be dehydrated and then ground up into a flour which can then be used as a substitute for baked goods that use bean flour or to thicken stews and gravies.
The beans can be cooked like peas, simply boiled until tender. They can be used in place of peas, beans or lentils in recipes that call for any of them.
Among the perennial vegetables that will grow well in cold climates, American groundnut is one of the most versatile and practical for cooking.
Other Perennial Vegetables
Here is an article that discusses several other perennial vegetables, 10 Perennial Vegetables for Colder Climates.
Written by: Marika Li