Questions on: Sweet Potatoes

Ron Smith, Horticulturist, NDSU Extension Service

Q: Are blackie and margarite sweet potatoes edible? I harvested some nice ones when I pulled out my vines. I appreciate all your columns on horticulture. (e-mail reference)

A: Thank you for the compliment on the column! As far as edibility, I don't know. I know the potatoes are not toxic, but they may not have the flavor you desire. Give them a try and let me know.

Q: I recently emptied my outdoor pots. To my surprise, I found that my chartreuse sweet potato vines had produced huge tubers! This is the first time this has happened to me. I’m thinking about dusting them, packing them in moss and putting them in the cooler at 34 to 36 degrees. If they do survive until next spring, how do I start new plants? Do you cut them up the same as a regular potato? I appreciate the help! I always enjoy your column, too. I was especially interested in the recent tree selection information. (Mercer, N.D.)

A: Before placing tubers in storage, they need to be cured for 10 days at 80 to 85 degrees or between 65 and 70 degrees for two to three weeks. The tubers should be covered to keep the humidity elevated. After curing, store the tubers at 55 to 60 degrees. Chill injury will result if the temperature is below 50 degrees. To keep the humidity high around the tubers, they should be covered with or put in a burlap sack that is moistened periodically. This is entirely different from the way white potatoes are stored. As for planting sweet potatoes, that is entirely different as well. You need to place them in hot beds about a month before the temperatures stay above 60 degrees at night. Cover the potatoes with damp sand and keep the beds at 75 to 80 degrees. This will cause slips to form, which are then removed and planted. I'm glad that you are a faithful reader and that the information is useful to you. Thank you!

Q: What is the difference between a yam and a sweet potato? While I was growing up, we always had a sweet potato vine. We put it in water and let it grow. Now all I can find in the grocery store are yams. I have one in water suspended with toothpicks, but it is only growing roots. It looks like it has eyes, so I’m hoping it might do something. Do grocery stores in Fargo or Moorhead sell sweet potatoes? (New Rockford, N.D.)

A: Yams and sweet potato questions often come up around Thanksgiving, but not around Valentine's Day! There is a big difference between the two. Supermarket outlets sell sweet potatoes 98 percent of the time. To end any further controversy (hopefully!), what the supermarkets are calling "yams" are, in most cases, sweet potatoes. Why? Because they have the taste most Americans want and are used to, as well as the texture of the flesh. Sweet potatoes are grown in the U.S., mostly in the South. Yams are imported from the tropical regions. Frankly, most of us would find the yam an unappealing object to gag down without a lot of doctoring first. It should be no surprise that the sweet potato produces roots because that is what it is! Even though supermarkets are not using the correct term, botanically speaking, when they refer to sweet potatoes as yams, they are forgiven because they are attempting to cash in on our lack of distinction between the two very different plants! To check out the differences between these two species, go to

Q: My boss grew sweet potatoes and now wants to know how to keep them until next year to plant in the garden. Some say to start them around Christmas and then plant them outside in the spring. Is it possible to store them like potatoes then cut them up and plant them in the spring? Will they dry out if you store them in a cool dry place? (E-mail reference)

A: Sweet potatoes are more difficult to store than the typical white or Irish potato. They should be handled as little as possible to prevent damage and brought into storage and curing immediately after harvesting. They can be cured by holding the temperature at 85 F and 90 to 95 percent relative humidity for four to seven days. Curing helps heal cuts and other injuries during harvesting and handling. If these conditions cannot be followed, then curing will take longer and the possibility of decay and disease will develop. For storage and holding, the temperature should be reduced to 55 or 60 F. That is usually accomplished by venting with outside air. The humidity should be kept at the 85 to 90 percent level. Under these conditions, must cultivars will keep for four to seven months. Expect a weight loss of 2 to 6 percent during curing and storage. I’m a non expert in this matter so all of the above information was pulled from USDA Agriculture Handbook 66 and other sources.

Q: Someone gave me a sweet potato vine that lost most of its leaves since being in the house. Can I make cuttings from the ends of the vine or should I just cut the vine back to the tuber and see what happens ? (E-mail reference)

A: Cut the vine back to the tuber and see what happens. Given a sufficient period of time, the plant may develop new shoots and produce an attractive vine for you. If not, check to see that the tuber has not rotted.

Q: Regarding the person in Jud who has a sweet potato that is growing, have you ever planted just the sweet potato? I have, and all that it does is make a very nice plant. There is nothing below ground. That plant should be cut into 6-inch pieces and rooted in moist soil or water. Right now is a good time to do this as they will have nice roots by Memorial Day when it is time to put them out.

A: How I love getting tips to pass on to other readers from practicing gardeners. There is no way I can grow everything, so when a gap exists, it is nice to know there is anecdotal information available on certain cultural practices that have succeeded with people like yourself. Thank you!

Q: If the person with the sweetpotato planting will take cuttings about 3 or 4 inches long and put them in water they will root in a couple days. Then plant them in hills in the garden like any other young plant after all possibilities of frost are past. Sweetpotatoes like mounds of soil. I start my sweetpotatoes like this all the time. Sweetpotato plants are quite expensive to buy so I've learned to make my own. This might be the only plant that roots faster then quack grass. (Gwinner, N.D.)

A: That's quite a reputation, to be faster rooting than quackgrass! Thanks for the information. All the readers will appreciate knowing of your sure-fire technique.

Q: I am spraying potatoes with Sevin but do not seem to be getting the job done. Do you have a better suggestion? (E-mail reference)

A: Try Neem, by Schultz or any other company marketing this product. It is a botanical that is not harmful to beneficial insects. Most likely the beetle has built resistance to the insecticide Sevin.

Q: We have planted some sweet potatoes and now something is eating the leaves. would you have any guess on what kind of bug that would do that? (E-mail reference, Morris, Minn.)

A: It could be flea beetles, or even slugs. Look for evidence of some kind--slime trails from slugs; little black bugs at the base of the plant. You can try spraying with Sevin dust to see if that controls the feeding.

Q: I have been wondering whether you planted sweet potatoes and if so what were your results. After your columns about sweet potatoes many people here tried them and reported that they had good results but that the potatoes got so large. I planted 14 plants and got 57 pounds. I know Gurney's Seed & Nursery is pleased with you as they sold a lot of plants to this area.

I also read that your radishes do not produce seed. I had some blooming at the time so I left them in the garden to see what they would do. They produced seed and for the past three weeks we have been harvesting the most wonderful radishes that have grown from the seeds. They are much better than spring radishes as the cool weather agrees with them.

As you can see, I like a gardening challenge. I am trying northern hardy peach trees at the present time. I will protect them like I do my roses. I hope to let you know in a couple of years that I have wonderful peaches. (e-mail)

A: Well, I'm glad to hear that everyone's sweet potatoes did so well. Mine produced lots of vine and enough sweet potato meat for one meal -- that's it! Of course they were under water for days a couple of times. This doesn't help crop production much!

Good luck with your peach experiment. I tried and failed -- the deer ate the whole two trees!

Q: Following is information for the reader who had some questions about sweet potatoes. Planting instructions: About one week before planting, mound soil in a row, cover this with black plastic and secure the edges down. Plant out the plants after danger of frost. When planting, cut a slash in the plastic and plant about 18 inches apart. Water the plants when planting and again a couple times in the following days.

You can now ignore them until frost, when it is time to dig them. They need to be laid to dry and cure in the sun and warm temperatures, so I usually dig mine around Sept. 12. When digging, be careful of skinning them as they keep better when they are blemish free.

Before frost, I cut a couple lengths of foliage and plant them in the house. I thus have a nice plant in the house for the winter, and I cut the plant up in the spring and root the pieces in moist soil to plant out again. A tuber that is sprouting can also be put in moist soil to produce cuttings. All the sweet potatoes need are sun and some 80° days. I have grown some that weigh over 3 pounds. (Berlin, N.D.)

A: Wow! Thank you for such good, detailed information about sweet potatoes. I think the largest sweet potato I grew was more like 3 ounces, not 3 pounds.

So, yes, I'll try them again, as the ones purchased in the store just don't measure up. Thanks for writing.

Q: This is in response to the reader who asked about sweet potatoes. A good variety to grow is the Georgia Jet. I start my plants in the house after Christmas, but I would not advise planting them outside until early June. I think you should try planting them again, and I am thinking about trying it commercially. (Fullerton, N.D.)

A: Good hearing from you. Yes, I'll give them a try again to satisfy my own craving for them. Let me know if you try them commercially. Wouldn't it be a kick to have N.D. producing Yankee Sweet Potatoes? Thanks for writing.

Q: A good supplier for sweet potatoes is Gurney's out of South Dakota, (605) 665-1671. Good varieties to try are the Georgia Jet or Jewell. They have given me 2-3 pound sweet potatoes. I think you should try growing one of these varieties and you will have good luck. (Groton, S.D.)

A: Thank you! I read your letter just before lunch and it has my stomach growling. Perhaps I could enjoy some "sweet potato pie" like I used to have when living in Georgia many years ago.

I am going to try them again. They're a good source of antioxidants.

Q: I would like to plant sweet potatoes and am wondering where the best place is to find seed for this and which variety would work the best? I would like to grow one that has a long storage period and a good flavor with reasonable production rate. (Williston, N.D., e-mail)

A: Sweet potato information is something you are going to have to pretty much fetch for yourself. I have no data that I can relate back to you. I grew some about 12 years ago in my own garden, and got lots of vine, but only pips for potatoes! They are a day length and temperature controlled crop. Long days, which we have in the spring and early summer promote vine growth, and short days induce root development and flowering.

I'm afraid you'll be frustrated with the results if we have typical Northern Plains summer weather. They like it constantly warm or hot to do well. Georgia, Texas and Arizona are all good producers of this delicious crop when I lived there. There are probably some cultivars that are more adapted to our seasons, but I just don't know what they are. Sorry!

Q. I live in the Fargo-Moorhead area and get seed catalogs from Gurneys and Fields. According to them, I should be able to grow sweet potatoes here. What are your thoughts on this?

Also, last year people gave me some seeds they had been given from Page Seed Company, Green, N.Y.; Michael-Leonard, Grant Park, Ill.; and Excel Seed, Chattanooga, Tenn. The Excel seeds are sold here dirt cheap. I had carrot and beet seeds. I planted extended rows with these seeds, and at harvest time you couldn't tell the difference. I buy either NK or Burpee, but that is a lot of difference from 10 cents a pack to $1.29 or more. Can you comment on this? Thank you. (Moorhead, Minn.)

A. Yes, you can grow sweet potatoes in Fargo. I have done it. Holland's in Moorhead handles varieties that would produce well in our area.

Packet seed prices are based on a number of factors. (1) Method of distribution—direct mail order, or through an in-store rack. (2) Whether or not the companies have a national advertising budget. (3) The fancier the packet, the higher the cost and fewer seeds, usually.

By law, all seed companies must meet certain purity and germination standards. When that minimum is met, differences between the companies on the same variety all but disappear!

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