let there be sweet potatoes: how to plant them

sweet-potatoesB ETWEEN A ROW OF CUTTING TULIPS AND ANOTHER OF ALLIUMS, on a mounded “ridge” of soil created for the purpose, the sweet potatoes were tucked in here a week ago. You have to love a seed or plant that comes in the mail complete with recipes: how optimistic, how confidence-inspiring. My box of “slips” included all the details on planting, sure, but also on making sweet-potato fries and sweet-potato pie, and I cannot wait. But there are probably just a few details to consider before I fire up the stove:

Unlike white potatoes, where you plant a “seed potato” whose eyes are starting to sprout, with sweet potatoes you start with bits of vine called slips. Glenn Drowns of Sand Hill Preservation Center in Iowa, who lists more than 100 sweet-potato varieties in his amazing catalog, explains the origin of the word slip:

“A slip is a single plant (with small roots) that is sprouted on the sweet potato root and then slipped off so that you may plant it in the garden to grow a sweet potato plant.”

sweet-potato-plantEach slip doesn’t look like much when it arrives—a piece of vine with some roots and maybe a leaf or two, usually a little pale and worse for the wear after days in transit. But it will quickly rebound if planted promptly according to some basic guidelines (that’s the above-ground bit of one a day or two after planting, above):

The more deep, loose soil you give the plants, the more easily roots (potatoes) will form, and apparently they will also be smoother if not expected to bump into to many obstacles when they grow. Hence the idea of creating a ridge (sort of an elongated hill), but a raised bed would be fine, too, or for that matter any well-cultivated area.

row-of-sweet-potatoesSpace the plants 12 inches apart within the row and rows 36 inches apart, because these things take off in wild, vining fashion. I don’t mind; both adjacent rows of cutting bulbs (the tulips, right, and the alliums, left, in the photo above) will soon go dormant, and since I don’t need to dig to plant or harvest the sweets, it works out well; the bulbs won’t be disturbed by this neighbor in between.

Gardeners in the north may want to pre-heat the soil by stretching black plastic over their rows, as in the audio-less video I happened on (below) from Johnny’s Selected Seed, piercing the plastic every 12 inches to insert a slip. I skipped the plastic; my one long recycled piece of it was called into duty elsewhere this year, so we shall see. [Update: I regretted skipping the plastic, as much as I loathe the stuff, because the vines rooted i along their stems and I got more small potatoes than large ones.]

Water each transplant in and firm the soil around it, and that’s about it…except one thing: If your slips arrive as mine did before the weather really settles, you’ll have to have some Reemay or an old sheet ready for protection. These are heat-lovers, not cold-hardy types.

In late summer, check the ridge by just digging in with your hand to see what’s formed, to judge readiness. Digging (as with white potatoes) is best done very carefully, to avoid piercing the roots; again here the ridge comes in handy, as you can basically “dig” by hand.

After digging, potatoes must be dried thoroughly to cure, and then stored at 55 to 60 degrees. With common varieties like ‘Beauregard,’ one that I am growing on my first major sweet-potato adventure, large potatoes up to 2 or more pounds are possible; other varieties vary widely in productivity, shape, size and even skin and flesh color. Just scan the list at Sand Hill to grasp the possibilities.

Want to try your hand at sweet potatoes? Longtime grower and mail-order source the Steele Plant Company in Tennessee is sold out for the season, as is Johnny’s Selected Seeds in Maine, but check in with Sand Hill to see if Glenn Drowns still has some of his “Season Closeout-General Assortment” specials left, the only thing he takes orders from after mid-May, and then ships late June into mid-July. You might get lucky. If not, order as soon as the catalogs arrive in early winter…to guarantee that homemade pie and sweet-potato fries in 2010.

  1. margaret anna says:

    Garden Friends,

    Just a little FYI, if you have outside lighting do not purchase low cost bulbs, they will often break off up inside of your fixture. I just replaced mine and was able to use needle nose pliers, to remove the broken glass. The outside garden lighting also takes up keep. Just thought you would want to know that.


  2. Sylvie, Rappahannock Cook & Kitchen Gardener says:

    I love sweet potatoes: good to eat, pretty to look at (especially with their morning-glory like flowers), and fairly care free. I am planting 50 slips this year, but I need to dig them out early so I have time to cure them. Otherwise, they don’t store well (spoken from experience!).

    It’s a great idea to plant them to spring bulbs that they can overrun. I’ll have to think about that for next year!

    1. margaret says:

      Welcome, Sylvie. Yes, the key to good storage is that curing, you are so right. It’s even true with winter squash, I think. Any damage to the skin or bruising or failure to let them dry properly and they deteriorate quickly. And a squishy sweet potato…well, not nice. See you soon again, I hope.

  3. Faith says:

    Well, I wish I’d seen this before. I’d never planted them and when I got mine, I figured it was all one thing and plunked the wad into the ground. Now that i look, it would appear I had actually purchased “one” group of slips. That would have been nice to be informed of in the catalog I’d ordered from. LOL


  4. Terra says:

    Now you are inspiring me to plant sweet potatoes, which I haven’t done yet.
    I am very pleased to have planted 2 blueberry bushes (Misty and O’Neal) this month. Isn’t it fun to keep adding new plants?

  5. Anna says:

    Harvesting last year’s sweet potatoes was the highlight of my gardening experience and I can’t wait to do it again this year…like digging for buried treasure, so fun. I recommend it for everyone!

  6. margaret says:

    @Faith: How long have they been in the ground? I’d be tempted to dig up and divide them into individual plants in the row if they are not more than a couple of weeks along.

  7. Susan says:

    Hi there-
    How do you keep the earwigs and slugs in check w/ all the mulch shown in the photo?? We did a light mulch and now are fighting WW3 w/ a banner hatch of earwigs!

    1. margaret says:

      I occasionally get an earwig in a pot here (and inadvertently bring it back inside in fall, oops), but no real issue outdoors at all. As you know, they love moist spots where they can hide by day (they do their troublemaking at night).

      I have read in bulletins like this one that you can trap them as you do slugs, with low cans (tuna type shape) with a little vegetable oil or vegetable oil with some bacon grease in it…or with rolled-up moist newspaper left overnight in the areas of the infestation, so that at daybreak they will crawl into it. You then have to go empty the traps, of course, drowning the earwigs in a bucket of water.

      One thing I will say about my mulching: I never put it up against the trunks of things, nor do I put it on super-thick (two inches perhaps?). I also manage to avoid issues with slugs for the most part.

  8. judy says:

    i have a question: how do i store sweet potatoe slips for next yr i bought the plants thru a nursery but want to save money by keeping some starts from my own plants but dont know how to store them for next yr………PLEASE HELP ME

    1. Margaret says:

      Welcome, Judy. I have never done it, but I guess I would try growing a sweet potato as a houseplant all winter. I will have to do some research, but frankly am just not sure. Good question!

  9. Karen says:

    This may be a bit late…. I just found your website and have started browsing the past entries. But sweet potato slips are easily started. Any time of the year you can “root” a sweet potato in water. I usually put one in a pretty but dark vase so the roots aren’t as obvious. The top of the vase should be just a bit smaller than the thickest part of the potato. Fill with water and sit the potato on the vase so that about half of it is submerged. Set this in a sunny window sill. Within days, roots will start to grow and shortly after that, the green vines will begin. Keep the water fresh and make sure the potato doesn’t start to rot. (If it does, pitch it and start over.) I usually keep one rooted in the kitchen window, just because it is a beautiful ivy type plant. But the leaves are edible and nutritious. Add them to soups or use them in place of spinach in many recipes. If you are starting slips for outdoor planting, start about 6 – 8 weeks before you want to plant. I have planted the whole potato before with good results, or “slip” the vines from the potato and plant them as you described above. Or if I were up north and concerned about a short growing season, I would keep the slips in water just long enough to encourage stronger root growth before planting to give them a head start. They are definitely heat loving plants.

    1. Margaret says:

      Welcome, Karen. This is great information, so helpful. Thank you. I am fascinated that sweet potato leaves are edible, and am going to harvest them when I do the tubers in an other week or two or three here, weather depending. And I will definitely grow some indoors as you say; I was going to do so in soil, like ahnging basket, but this sounds easier and more fun. See you soon again, I hope.

  10. Your blog is the best. It’s like reading a letter from a friend. I grow my own slips from a sweet potato plant, just like Karen. Sweet potatoes are fine if you can get one to grow. But they are treated to discourage sprouting in the grocery stores. So, if a store bought potato won’t grow, go to the Farmers Market or visit an organic farmer for starter sweet potatoes.

    After your first harvest, you can keep them going by using your own potato. Put a potato in a glass of water. I do this in late winter when it’s nice to see ANY garden plant grow. Keep slipping off starts from the Mother plant and keep them in a jar of water until it is time to plant put side.

    1. Margaret says:

      Welcome, Norman. In the cold zones (like here) we plant them as the weather starts to settle so that they don’t get touched by frost, so sometime on May. Mine arrived a little early in the mail, so I used a piece of floating row cover (Reemay fabric) to keep them protected at night at first. I don’t feed mine much since my soil is well-prepared with compost added each year, but you can get good results with the addition of a balanced formula (I’d use all-natural organic, not chemicals) or one slightly higher in the middle number, which is Phosphorus. You do NOT want a high dose of Nitrogen, fyi. Work some of the fertilizer in before or at planting time, then add the rest (scratched gently in beside the row) when the plants start to put on new growth, once they have adjusted to their planting.

  11. Stephen Ahern says:

    Last year, my wife and I planted the sweet potatoes in raised round wire cages 2 feet high and 3 feet diameter. The inside of the cage is covered with “weed block” fabric. At the end of the growing season/harvest time, we open the cage and hand dig the sweets out (no digging with tools). The trouble we had last year, was a vole (field mouse) got into each of the cages and made tunnels through the dirt to the sweets and ate a hole in them, my wife was not happy. This year we are trying to grow them in a long cage made of 1/4 inch “hardware cloth” (wire screen with 1/4 inch openings) and we figure that the little monsters will not be able to get in this year. The cages are 2 feet high, two feet wide and 14 feet long, bottom is also closed with the same wire screen, Well actually it is in a corner of the garden and it is 8 feet long on one “arm” and 6 feet long on the other “arm” BUT still “one cage” sort of like an “L” shape. We fill the cage up to the 18 inch line and plant the slips (this year we purchased potted “slips”) one plant every square foot (so we should get in 28 slips). Then when the vines start growing over the top, we add the last 6 inches of soil to give the plants more room to grow tubers.

    To get some slips for the following year, you could just take the “ends of the vines” 6 inches or so; when you are harvesting the tubers, and place them in water; they will grow roots, keep changing the water (to keep them fresh); when the plants start to get really long, cut off 6 inches and put that it water, and keep them going all winter, until you are ready to plant them in the spring.

    1. Margaret says:

      Welcome, Stephen. Yes, I have had critters gnaw on the tubers sometimes, too…but I am hopeful for a good harvest this year. Fingers crossed. I may try keeping slips growing someday — thanks. See you soon again.

  12. Fla.Dirt Dog says:

    My sweetpotatos have been in the ground about 6 months. I dug one vine up and had about 12 small tubers on it.. In that length of time,I figured they would be bigger. Do I need to let them go a little longer? I’ve seen them small like that in the grocery store so I guess thats normal.How long do I have to let these little things cure?

    1. Margaret says:

      Welcome, Fla.Dirt Dog. You have a better climate for them than I do, but here they take about 100-110 days (I have read that they can take up to 140, depending on the variety, but my relatively short frost-free season wouldn’t be a good match for such a slow-to-harvest variety).

      A few things that I know of can affect the development of the underground roots, including too much Nitrogen fertilizer (which makes more green topgrowth than tubers — and can cause stringy-looking potatoes) and also too much water late in the growing (generally they like to be hot and dryish once the vines are in full force and have really spread out above-ground). Some sources even say no water the last several weeks or month before harvest (versus plenty while the plants are developing the first month or two).

      Overcrowding can also affect the outcome — spacing the slips too tightly at planting time.

      I’m interested that yours have been in 6 months — 3 or 4 is more typical. This Texas A&M factsheet answers lots of sweet potato questions, including how to cure them.

  13. Rachel says:

    I just found some slips at Walmart and I planted them with gladiolas. I figure even if I don’t get any tubers they will make a nice ground cover for the glads.

    1. Margaret says:

      Welcome, Rachel. Why not? As you say, they will be beautiful in the meantime. Mine are starting to perk up.

  14. Ohaider says:

    Can you please explain how to cut a sweet potato to get alot of slips without putting in water but planting in the soil directly?Thanks in advance

    1. Margaret says:

      Hi, Ohaider. I have not seen it done with cut-up sweet potatoes, but with whole ones put in a heated bed inside a greenhouse or some other heated propagation set-up so that the soil stays 75-80ish. This Purdue University pdf explains. You bury the whole potato, and keep it warm (in the north this requires the heating of the propagation bed) and eventually get the shoots. I have also seen the water tactic, partially submerging the whole potato in water.

  15. Danielle says:

    I notice that you recommend removing black plastic sheeting used to heat up soil elsewhere on the site. They don’t seem to be doing this in the video. Are sweet potatoes some kind of exception to the rule? I’m concerned about watering through the plastic.

    1. margaret says:

      Hi, Danielle. I hate the plastic, but for the sweets leaving it in place is better so they don’t root in all along the vines and make smaller potatoes as a result. Water will get in through the Xs or slits you use for planting.

  16. marcus peake says:

    all of your comments and replies have been helping me I have just recently harvested sweets over about a month I bought 3 tubors from the local store who ordered them in for me 2 have taken over the whole plot and one is still small I planted the whole tubor in each case many many sweet potatoes is the result some the size that I have never seen maybe in your lingo 3 to 4 pounds and now after all your imfo am looking forward to nxt year we only get a couple of weeks of frost driest state in the driest continent and these plants are 500 yards from the beach thankyou

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