The true yams (Dioscorea species) vs. Sweet Potatoes (Ipomea species) have for many centuries been staples for people in subtropical and tropical regions of the world. They are extremely undemanding as regards moisture and soil (though do even better when given some care), their upright vines grab fences vs. sprawl and thus take up little space in the garden, and their tasty tubers are more nutritious than the potatoes that don't thrive in summer in subtropical areas. Another advantage is that the tubers are left in the ground until needed....they never get woody. I once let a Caribbean yam ( name' ) grow for 5 years until its vines killed a few beloved climbing rose...when I finally got the tuber out of the ground, it weighed 65 pounds!!! I took a 35 pound chunk to a meditation group to share with members, and a woman from Puerto Rico was delighted to take home a huge chunk. She told us it is a staple there, and she gave me the name of a recipe to look up...a seafood and yam stew. I made a batch....yummy!
Like the air potato (Dioscorea bulbifera) it has the potential to become invasive due to the numerous aerial tubers that form on the vines each fall. Just be sure to gather them to save for planting or to feed to goats or pigs or cattle. These ancient crops can do much to make a mild climate urban farmer self sufficient in very nutritious high-carb tubers that when cooked taste a lot like an Idaho potato. They are UNrelated to Sweet Potatoes and so are NOT sweet nor do they bear edible leaves.
The photos are of what is likely African Yellow Yam (Dioscorea cayenensis) that a few years ago my friend Tim and I found while trying to harvest Chinese White Yams growing on the north bank of the Hillsborough River in Sulphur Springs. Bear in mind that the large tuber in the photo had already yielded several big chunks for meals in the days preceding my taking the photo yesterday.....when right out of the ground it easily weighed 20 lbs. Even better, it was the size of the aerial tuber in my hand when I planted it two years ago! The vines die back in fall, frost or no frost, signalling ideal harvest time. But the tubers can be dug up and savored year round, making them ideal for food self sufficiency gardeners like me.
When raw, they are slimier than okra when sliced, but baking, boiling or frying turns this protein rich plant mucilage into a starchy dish that can be compared to a baked Idaho potato. My favorite way to serve them to me and friends is to brown thick slices, slowly and covered (the steam helps to cook the mucilage) in coconut oil and roasted sesame oil with garlic and sea salt. I just use a sharp chef's knife I dumpster dived to cut the coarse rind off of each slice before cooking. I grow several kinds of yam, and cooked this way, they have been a real hit at potlucks or served to friends over for dinner for years now.
In one photo you will see my hand behind one end that has lots of roots on it...in another photo you will see it severed. True yams are self replicating "food machines"....save that severed end, like it dry in the shade a few days, replant about 6 inches deep, and in two years you will have a giant tuber all over again!
The easiest way to grow a true yam is to buy a name' from the Hispanic veggies section at your grocery store and plant it at the base of a sunny chain link fence. Even if you never dig it up to eat, the vines are lovely each summer and many visitors here ask me what the beautiful vines are. I will attach a photo of vines of my Filipino Purple Yam "Ube" (Dioscorea alata var. violacea ) to give you an idea of the true yams lush graceful beauty.
Sure they are not native here, but neither are we....and we need to eat! Just take steps to insure the aerial tubers do not invade native forests etc. as part of responsible urban farming, and treat yourself and your family to tons of tasty tubers!