This relatively unknown tuber is one of the main reasons that the Pilgrims survived in America. This was one of the main foods eaten at the first "Thanksgiving Feast". A staple crop for the countless tribes of the Eastern US, Hopniss (as it is sometimes called) is a nitrogen fixing protein rich (aprx. 23%) tuber of the legume family. It behaves much like Crosnes and Sunchokes in that when you harvest you will inevitably leave some in the ground, these will plant themselves for the spring. All you have to do is thin to the desired spacing once they sprout. Groundnuts like rich moist soil and something to climb on. The nitrogen nodules on these are MASSIVE. Its tubers grow in a chain like fashion for many feet in all directions. 1 tuber will turn into 12 -30 tubers.
The short vines host GORGEOUS pink and white flower clusters. The vines twine themselves up anything they can and host pinnate leaves that look like pointy pea leaves. They can form thick mats of leaves as the vines crawl in and amonst themselves.
Tubers: Tubers are best cooked over long periods of time to improved digestibility. They lend themselves well to being thrown into a roasting pan with a hunk of beef or chicken. Stews are a good use of them as well. You can slow roast them, mash them up with spices and then broil the mash to make a sort of refried bean.
In the wild they are used to growing very closely, so I tend to replicate that. From one tuber 2 -7 chains of tubers will extend out in all directions, I plant them closely to make them more densely fill the soil when I harvest. By growing them in mounds you restrict the reaches of the plant and encourage them to grow more densely. Planting at 4" - 8" spacing seems to lead to good results, the roots like to grow around things in the soil. Plant them 2" deep. If you do not plan to mulch then make sure that you leave enough room between them to enable you to keep the weeds back while their vines begin growing. Like more perennial veggies, I prefer to plant into raised mounds to improve the ease of harvest. I make a furrow atop a raised mound and drop them into the furrow at the desired spacing. I then place a bamboo stake next to each one and cover them all up. This also helps me know where they are when I weed the bed before the vines sprout.
The vines come up in late spring so make sure you have there location marked so that you can avoid hoeing the sprouts. I mulch very heavy and leave an unmulched area directly over the row I planted (at the apex of the mound); this way the only part that needs weeding is that small gap between mulch. I lay a drip line down this gap before the groundnuts start to sprout. Once the vines are a good six inches high I will do one last weeding and cover up the unmulched part of the row.
Use a spade fork to loosen the soil all around where the vine comes up from the ground. Then you can either gently lift up the whole plant with the fork and shake the dirt loose OR you can find the original tuber and follow all of the "root chains" with your hands as you gently lift them out of the soil.