Plant of the Week: Sweet Potato

Sweet Potato (Ipomoea batatas)  Photo Credit

As Thanksgiving draws near, I have begun to think about holiday meal favorites and for my family, sweet potatoes are must haves with the Thanksgiving turkey dinner.  Now, I don't know about you, but for years I have been confused about the difference between sweet potatoes and yams.  I thought this would be a great time to investigate sweet potatoes a little deeper and help clear the confusion surrounding this sweet Thanksgiving favorite.

So, do you know?  Are sweet potatoes and yams the same thing?  The answer is no... and yes.  Ah, more confusion!

Let's look at the 'no' answer first.  Botanically, sweet potatoes come from the same family as morning glories (Convolvulaceae) and originated in the tropics of Central/South America while yams belong to the monocot (grasses are the best example of monocots) family of Dioscoreaceae and originated in Africa.  Our sweet potato (yam) is a soft fruit that is yellow/orange in color and very small compared to the firm fruit of the African yam that averages 5 - 11 lbs but can weigh as much as 55lb!

Obviously they are very different both as plants and fruit, so why is there a 'yes' answer to my question?  In order to distinguish a distinct variety of sweet potato that is grown in the southern US, the common name yam was given to it and that name has stuck.  Reality is, with very infrequent exception (at least in my area) all fruit labeled 'yams' are  really sweet potatoes.  The USDA now requires all yam (sweet potatoes) to be labeled with both names to eliminate confusion... so if you are confused check store labeling.

Sweet potatoes are planted from vine slips (or cuttings) and not from seed.  They do not tolerate frost or cold soils so should be planted only after all chance of frost has past.  Plant the slips in full sun and well drained soil 12-18 inches apart.  Keep them well watered for best production, but the roots will develop rot which will destroy both the root and the 'fruit' if they sit in saturated soil. 

Recent short season varieties (90 day maturity) have expanded their range to include us northern gardeners, but keeping the soil temperature high enough to get a productive harvest (about 75F) can still be a challenge.  Northern gardeners may want to consider planting in mounds or raised beds to raise soil temperatures and protect plants in a tunnel or cloche during the cool start and end of the growing season. 

Vines will remain green until the plant is killed by frost, but harvest the tubers before frost to protect the tuber. Let harvested potatoes dry a couple of hours in the shade before storing.  Dirt can be gently brushed off the tuber but do not wash until you are ready to use them.

I hope I have cleared some of the confusion surrounding sweet potatoes and yams, and also given you a new plant to think about trying during our next gardening season! :)

Happy Gardening! :)