Sweet potatoes left in the ground...?

Hello all,

Okay, I have read a lot about sweet potatoes here on Permies, mostly about what an excellent ground cover they make. I heartily concur! In past gardens I have happily made use of their potential to completely suppress all weeds in an area, while producing delicious tubers, and at the same time not interfering with other, taller growies intermixed with the sweet potatoes. For instance, several times I grew sweet potatoes, okra, and tomatillos together in one bed with good results.

But now I am reading about people using sweet potatoes as a soil improvement species. Makes sense: massive root structure that branches wide and deep and makes big fat chunks of starch just ready to decompose into little pockets of soft goodness throughout the soil. Excellent. I had not until know considered using sweet potatoes in this manner - as a ground cover and a clay-busting "crowbar" species simultaneously - and I am eager to give it a try!

So, my question is: if I plant sweet potatoes but do not harvest them, or harvest only a few near the surface and leave the rest in the ground, given my climate (zone 7B, upstate South Carolina, which means cold winters but still a very shallow frost line), what are the chances that all will rot in place vs the chances that some or all could sprout new sweet potato vines next year? I suppose that I would be happy with the results either way, but I would love to know what to expect if someone has any experience in this space...?

My secondary question: on a different thread in this forum, concerned with growing potatoes and sweet potatoes in a no-till system, another Permies poster once wrote something seeming to suggest that leaving unharvested potatoes (I think she meant white potatoes, not sweet potatoes) to rot in the ground increased the likelihood of a blight infestation. I asked her to clarify her comments in that thread, but never got a reply. Does anyone know about this? Could it apply to sweet potatoes as well? Is it anything to worry about in the first place?

Thanks! All comments are appreciated : )

I'm in Zone 8 and have had sweet potatoes grow back from tubers left in the ground over the winter. They are perennial in warm climates. If they freeze in the ground they will die and rot. Given your conditions I would guess that some might survive and regrow, but you won't know for sure unless you see it happen!

i have never grown sweet potatoes before (have some that sprouted last week potted up)..going to try..zone 4 here.

I have however often left a few white potatoes (or other color regular potatoes like red or blue) in the ground and they do grow new crops the following year..not perennial but the potato in the ground is actually the seed for the new crop.

Late Blight, p infestans, infects solanacia crops. Sweet potato would not be infected.

I've left sweet potato in the ground. Some will come back, some will rot. If you have enough sweet potatoes in the ground, consider sending a pig after them. The pig will tear it up much better and faster than the potatoes.

in your climate there is a slight chance they come back. If they do come back its not really a big deal unless you planned on using that area for something else.

no concern about pests or disease where you are. my biggest problems are the deer love the greens and the gophers love the tubers.

Okay, so it sounds like the consensus is that it depends on climate (doesn't it always!) and that I am probably somewhere right on the line between the rely-on-spontaneous-sweet-potatoes zone and the buried-rotten-tubers zone. Actually, some good mix of the two would probably be ideal for me. I will be sure to post back when I have first hand results to report.

@Ken - Excellent point. Actually, that is so obvious; why didn't I think of that? But for the sake of argument, then, let's forget about sweet potatoes and talk about leaving white potatoes in the ground (which do, as someone pointed out, come in a variety of colors, so Irish potatoes, Incan potatoes, whatever you want to call them ...Solanum tuberosum). Will that increase the likelihood of Late Blight? My reading online says yes. Anyone have any experience on this? How prevalent is potato blight in the southeast U.S. in 2012 anyway?

Phytophthora infestans is indigenous to all soils in the world. All that is needed for the organism to flourish is the right conditions: cool and damp. Part of the reason it is called Late Blight is that towards the end of the season, it tends to be cooler, giving the organism more chance to flourish. If potatoes are left in the ground and succumb to infection, they will turn to mush in a couple of days. If its cool enough, growth can be slowed, giving the organism a chance to over-winter inside the tuber. If that potato is able to grow, it can spread the disease. Spores are produced on the leaves in vast numbers and are spread by wind. In '09 I grew a dozen types of potatoes. The summer was cool and rained like hell. I first found Late Blight on a group of tomato plants. Within 10 days all the tomatoes (200+) and all the potatoes (300+) were laid waste. I was able to dig up a wheelbarrel load of potatoes from a side field. The main field was planted later and had not yet produced tubers bigger than marbles. Within a few days, those tubers I had dug up, washed, dried, and stored were starting to turn to mush. Shortly thereafter my path led me away from that farm-I can offer no follow up observations.

If you had an infestation last year, it would be prudent to plant this years crop in a different location. Take Late Blight seriously-if you don't you are asking for trouble.

@Ken - Wow... I wouldn't want to meet up with any P. infestans in a dark alley, that's for sure. Your situation could only have been worse if the blight had also killed your dog and raped your daughter. And don't read any sarcasm into that, either; it sounds like seriously scary stuff! I really didn't know that outbreaks in this country could be so bad. I will surely take your warning to heart.

Fortunately, I've already decided on a technique for growing potatoes that should lessen the likelihood of outbreak. I started a different thread previously about how to integrate potatoes and sweet potatoes into a no-till system. The consensus reached is that it's easier not to; just segregate them into their own beds devoid of any perennials and plan on tilling those areas only. Specifically, I think I'm going to try small, "sacrificial" raised beds. In the spring time, set up a 2' tall, 2'-3' diameter ring of fine hardware cloth in any open spot. Optionally, line the inside with weed blocker fabric (vertically, I mean). Fill it half way with a homemade light potting mix (soil, sand, compost, shredded leaves) and plant potatoes, radishes, fast growing herbs, and any fast growing beneficial weeds that you don't mind destroying. As potatoes grow and others are harvested, pile up mulch in successive layers. Depending on climate and weather, be prepared to irrigate. Come potato harvest, disassemble the ring and let it all collapse onto the ground to be sifted through for an easy harvest that should also ensure 0% missed spuds. Rebuild, rinse, repeat.

I hope that this should work well enough for my Irish potatoes. For sweet potatoes, I'd considered doing the same, but I'm now thinking I might instead use them as a permanent ground cover over large areas. I could count on harvesting a few tubers closest to the surface and not even worry about the rest; just call them soil improvement. If a small % of those spontaneously sprout new sweet potatoes the following year (which sounds like about what I might expect), so much the better.

Late Blight is what caused the Irish Potato Famine. Google it.
The outbreak in '09 devastated tomato and potato crops in 17 states in the northeast. It was nearly impossible to find a tomato at a farmer's market.

Brenda Groth wrote:i have never grown sweet potatoes before (have some that sprouted last week potted up)..going to try..zone 4 here.

I have however often left a few white potatoes (or other color regular potatoes like red or blue) in the ground and they do grow new crops the following year..not perennial but the potato in the ground is actually the seed for the new crop.

do you have a cold hardy variety?
please do let me know the results of your attempt, i am also in USDA zone 4...

I have grown sweet potatoes for many years in the sandy soil of central Florida. I have never replanted, I just leave any little ones I find while harvesting in the fall and a new crop comes back. I have only done this in a small garden space shared with many other vegetables. I grow lots of tomatoes, peppers, lettuce, etc. in the space with the sweet potatoes in the winter and let the sweet potatoes take over the bed in the summer when it is too hot to grow other things. I get lots of sweet potatoes and the soil is ready to plant my winter garden after I dig up the sweet potatoes.

What am I doing wrong? In south carolina I should be the sweet potatoe queen - but I'm the sweet potatoe vine queen. Granted, the voles get a lot of my tubers but mostly I just grow vines; in fertile soil, in sandy soil, whatever. I have tried letting the vines wander at will and I have tried putting a little soil over the top at intervals and I have tried just burying large quantities of the vines. Only one or two pathetically small sweet potatoes.

The one thing that I have not done is purposely fertilizing them as I have always heard that they don't like a lot of fertilizer. Any tips for me?

I've read that pinching off the vine tips can help promote tuber formation. Plus the vine tips are very nutritious and can be added to salads, stir-fried, etc.

@Jeanine - Hmmmmm... That's a tough one. Truth is that I only have a couple of years growing sweet potatoes beneath my own belt, from my days urban community gardening at my old residence in northern Virginia, but I can't say that I've ever had that problem. I would start with maybe half a dozen sprouted whole sweet potatoes, spaced evenly down a 12' x 3' raised bed that had been tilled and amended with lots of leaf mold and a little bit of organic fertilizer prior to planting; mulch with a good bit of straw; and wait until the first signs of frost before harvesting all at once. That's it. And every time I planted them, I got plenty of spuds for my trouble. You are certainly correct that you live in a suitable climate for growing sweet potatoes. I assume your comments about piling soil on top of vines here and there reference a method for forcing the plants to put down more roots? I've not heard of that before; I just let my vines go where they wanted to go. But you said you've tried that as well... And you don't think it is a deficiency in your soil texture or fertility...

This probably isn't much help, but about the only useful thing I can think of to suggest is this: are you sure you dug thoroughly enough at harvest time? In my own experience, as described above, come harvest time I would dig up the plants and get a few spuds. Then dig deeper and get a few more. Then dig left, right, etc. The point is that each season I ended up basically double digging the entire raised bed, every square inch of it, and down to a depth deeper than I'd tilled in the spring to start with. But no matter how sure I was that I'd found the last spud, if I kept digging more I would invariably turn up another. They really go down deep and hide in the corners far from the crown of their vines.

Like I said, probably no help to you, but it's all I can think of to suggest.

I thought I would also add for those who don't know, the greens are also edible

Matthew - thanks for the tip - it is very possible that I have never dug down deep enough - I know I have never dug as deep as you are talking about.

@Jeanine - They definitely don't just hang around near the surface right below the crown of the plant, as Irish potatoes sometimes do. At least, not the variety of sweet potatoes I've planted before ...which variety I couldn't tell you what it was, unfortunately. Use a good turning fork, in addition to a shovel, to work through the soil and find the spuds. You'll damage fewer that way.

Since sweet potato vines form roots (and eventually tubers) wherever they make contact with the soil, one thing you can do if you are only getting a few small potatoes is to lift the vine mat off the soil every couple of weeks to break up any adventitious roots that are forming. This forces the plant to store all of its surplus energy (i.e. tubers) into the main roots rather than scatter it over a myriad of adventitious roots forming under the vine mat.

@Mike - That's very interesting. I hadn't thought about that. I notice that sounds like exactly the opposite of what Jeanine has tried in the past. Perhaps she will get better results your way!

I have at least one volunteer sweet potato coming up from last year. I have already planted a few slips, so I can't wait to see how they compare. I'm in central Ky. The volunteer came up next to and old hugel bed, and I heavy mulch everything with wood chips.

I am somewhat of a conoisseur of sweet potatoes, and have basically been eating them most every day in their storage season for many years. I often say that if I had to be turned loose in the Southeast and I could only take one cultivated plant with me, that would be it.
My hunch is that they are native to a region with well-drained soils and the climate broken up into rainy and dry seasons. The vines grow out in the moister part of the year and the tubers preserve the plant through the dry. So I think that soil drainage and moisture are key to perennializing them as well as cold. In a sandy soil with a relatively dry winter, such as in southern Florida, it would be much more likely, and perchance possible on sandier sites in a dryish winter further north. But I've always been on clayey soil when I lived in GA and hardly ever saw a volunteer. And bear in mind they are not just frost-tender, but "ultra tender", comparable to, or moreso than things like eggplant, peppers, or melons. Anything below 55 or so and the plants quit growing and below 50, they will droop....especially new ones just planted (This is one big secret to growing them, especially further north....don't rush it!) Even stored below 55 or so, the tubers go bad much more quickly. (I usually keep mine right in the house.....my slogan is "my food security is 200# of sweet potatoes under the bed!") So you can imagine their chances left in a cold wet clay through a wet Georgia winter!
The other thing is that they are perennial by nature, with sprouts coming up from the same tuber year after year. Roots form above the tuber from the sprout directly, and this is how they are usually propagated, by breaking these off and planting them, but they will also form elsewhere on the tuber, and if you plant the same tuber year after year, it will just go on getting bigger and bigger! I've heard of people growing 50 pounders that way! (Not worth much for eating purposes though.....I usually find the biggest ones to be the most fibrous!). So for people who DO have luck with getting them to perennialize, one challenge would be to force them to grow at least some new tubers. The vines do root at nodes if they touch damp ground, but tubers might not grow there while the vine is maintaining a good connection with the original root.....so some judicious pruning and layering would help with this. Incidentally many varieties will root easily from vine cuttings....I sometimes keep them through the winter this way, as house plants in hanging baskets....and then clip up the plant into a bunch of cuttings in the spring. The varieties that do this tend not to be the ones to sprout readily from the tubers....usually I keep the small ones for planting and put the best of these in pots, or perhaps a warm coldframe, in the spring to sprout. Either way, keep them warm!
And yes....eat the greens! They cook up bland and soft, comparable to spinach or chard. And keeping the vine tips pruned helps curb rampant growth where it might be unwelcome, and a moderate amount doesn't seem to harm the crop of roots....

just about to start with my own sweet potatoes. this is just the thread I was looking for. thanks to all who have posted such great information and suggestions! what a resource this is!

@Jeanine

Try a shorter-season variety. We've grown more tropical types (like, from the Caribbean) and had them fail to make many tubers despite luxuriant growth. Look up cultivars for further north and see if it helps.

@Matthew

I grew them in zone 6b/7a outside of Nashville. Some of them often came back from the ground the next year, though they were planted in a mulched garden (though only a couple of inches deep). Pretty good for a tropical root.

@David - That is encouraging for sure!

@Alder - Lot's of good info. Thanks for joining the discussion : ) In my case, I am interested in perennializing sweet potatoes strictly as a ground cover, maybe with some leaf harvest thrown in to boot for my kitchen and/or my critters. Though I understand that sweet potato leaf is a major crop in parts of Africa, Asia, and India, I think yours is the first 1st-hand report of the eating quality of the leaves I've read. Again, thanks. As I mentioned above, if I can indeed get them to perennialize, I will also grow a few as annuals in separate, specialized beds for a root harvest.

Great discussion! I'm in the middle of sweet potato planting and just came in to refresh my knowledge. I'm in my third season of gardening and am also a sweet potato fanatic - eat one daily for nutrition, fiber and to ward off the cravings

My soil is friable clay coated with a mix of weeds and bermuda grass (if that makes any sense - it was worked by original owners as a garden so it's not super hard and sticky like the red stuff 2 feet down in my yard. But it doesn't seem to have much organic matter or worms). My first year I ordered Beauregard slips from Sow True Seed in Asheville, turned over the soil one spade depth, hilled it up and stuck the slips in. The foliage proceeded to take over the garden (wonderful!) and when ready to harvest I found HUGE mounds of sweet potatoes directly under the plant. It was like a bunch of bananas, so tight and close to each other, in many cases I had to just lift the whole thing en masse - not an easy task. The potatoes varied in size from small to larger than grocery store size (the largest as big as my size 10 shoe - lol). I guess ignorance is bliss, but sadly they didn't overwinter very well, or more likely I didn't store them properly.
Last year I forgot to order slips and was distracted by other things.

So what I'm wondering, because I'd like to perennialize this batch, is whether I'll be able to harvest the potatoes without damaging the whole root system. I didn't know that they're supposed to grow scattered about - lol! And in order to get the potatoes to spread out a bit should I double dig this time - I don't know how deep I need to break up this clay - especially since it was mentioned that sweet potatoes are valuable for that very purpose. I've ordered the same slips this year because they were so delicious!

If you really want roots scattered all over, try putting some soil or heavy wet mulch over the vines here and there. But most people (including me) who want a convenient yield of roots want them not to do this, but to form a clump of roots under where the original cutting is planted, as you describe. That way you don't have to dig up the entire area to find all the roots. Given your location I doubt you'll have many roots successfully overwintering.....for the best chances choose a sandy spot and mulch them heavily....perhaps including a piece of plastic to keep off the excess wet? Seems to me just as easy to store the roots indoors....

Thanks Alder - very interesting. So clustered roots is normal and preferable for the edible harvest - check. I personally don't want them scattered I just wondered why the difference. As for overwintering them in sandy soil - ha! All I have is clay. However I'm intrigued by the idea of overwintering them inside. So are you suggesting transplanting the already harvested plants into pots and taking them in?

Or just take clippings of the vine and start rooting them inside over the winter? But that would be 6 months before xplanting to the outside garden, then I'll be scared of the "invasion of the body snatchers" pods! Oh, duuh, you mean keep the sweet potatoes under the bed until late winter and then cut them up and grow slips.

At any rate, I forgot to mention in my first post that I'm liking your "under the bed" storage idea - it's otherwise wasted space and like you said, I'll be comforted with sweet dreams by the thought of my rich bounty underneath my mattress :beerchug

Usually I try to keep some of the smaller ones....sound and undamaged....for planting in pots or perhaps in a warm coldframe in the spring to sprout. You don't want to cut them, like white potatoes, and when the sprouts come up a couple of inches, you pull them carefully, perhaps holding the potato (which is set just under the surface) with your other hand, and the sprouts will break free of the potato. There will usually be some roots coming directly from the stem of the sprouts. Set these out in the garden and keep them wet for the first few days till they take. The other way is to take cuttings of the vines in the early fall, setting them one node down in damp soil and let them grow out all winter as house plants---they look nice draped in a hanging basket in a sunny spot (but watch out for spider mites!). Then in the spring cut these up into two-three node sections and start up a bunch of cuttings this way for planting. As I said above, usually I do a few each way, because sometimes one way will work and the other won't.....
I suppose you could plant the whole small potatoes, like white potatoes, but the danger with this is that it might just end up growing larger, rather than more in number. The older and larger the potato is, the more likely it will by pithy or fibrous or otherwise less than the best....

The reason behind putting the potatoes under the bed is that the most common mistake in storing them is to have them too cold. 55 minimum, and warmer is OK. So no cold cellar or root cellar or anywhere you would put white potatoes, apples, cabbage and such like. Somewhere "inside" the space you are keeping heated for yourself through the winter is better. Incidentally, the same is true for winter squash and pumpkins. All of these should keep well into spring if cured and stored properly....

@Susan - Congratulations on your initial, very successful year. Alder is exactly right, of course: if you are primarily interested in a root harvest, then you should be happy that yours were growing so tightly concentrated beneath the original plant. How convenient! In my own past experience, that wasn't so much the case: the more I dug, the more I found sweet potatoes hiding in all corners at all depths. But there could be your answer: harvest only the most convenient and obvious roots nearer the surface around your original plant, assume that there are more scattered further afield, and see if they reappear on their own early next summer. If you don't see sweet potato vines by a certain date the second year, then assume that any left in the ground have rotted over the winter (all the better for your soil!), and plant new slips. If you save a few of your own sweet potatoes over winter for growing new slips, fine. If you buy new slips instead, fine too; they're not expensive. In the past, I grew slips by taking whole sweet potatoes, laying them out on top of a couple inches of straw, covering them with a couple more inches of straw, and watering them occasionally during the very late spring. By early summer, as the first vines poked through the straw, I just buried the whole sprouted sweet potatoes in my garden. This produced vigorous plants and large harvests in my own case. But of course, you could pick off the new slips and plant them individually, as Alder described above.

In this scenario, you wont be doing any more digging than what was necessary during your fall harvest, at least not until your drop-dead date has passed the following summer and you go to plant new slips of your own. Before that, you don't want to disturb anything just in case your prior years root system has gone perennial and is preparing to break surface again, which from my perspective is the ideal outcome. Worth a few year's experiments, at least, to see if it is possible in your climate. The ideal goal of perennialized sweet potatoes is ideally suited to a no-till system (which is best approach anyway, in my opinion).

As for your disappointing storage results, Alder is of course correct on that point too: sweet potatoes, like winter squash, appreciate warm dry storage at room temperature or just below. But there is another consideration, as well. During the fall harvest season, there is a delicate dance to be danced. You want to wait as late as possible so that your vines grow the biggest possible tubers. But, if you wait until there is significant, visible frost-kill of the vines, the sweet potatoes you dig will be compromised. They will look and taste fine when first harvested, but their long-term storage potential is reduced. At least, so I have read.

@Alder - You wrote "All of these should keep well into spring if cured and stored properly..." I know what you mean about curing winter squash: after harvesting, they are left sitting in the sun for some extra days (up to a week?) before storage, so that their skins harden. Do you do the same with sweet potatoes? I didn't know that. Inquiring minds want to know...

Thanks guys - you're so helpful! And I found this which really helped me understand the growth habit of the sweet potato.

http://www.soilandhealth.org/01aglibrary/010137veg.roots/010137ch25.html

Scary almost! I see they can go 4 feet down - have fun digging Jeanine - lol! This year I'm going to pay more attention to the structure of my roots and see if there's more down under from the cluster at the plant.

It makes sense now, that the plant propagates thru the root buds on the tuber, not from the upper root system (barely made it thru Biology 101 here). It's possible I missed some tubers but here in "Almost Zone 8" I've noticed that semi-tropicals like Lantana will overwinter one year and not the next. It doesn't seem like we have much of a frost line here but I guess I shouldn't count on this plant coming back on its own so I like both of your ideas for propagation. I'm going to try both, leaving a few in the ground and starting slips next winter. And like you said Matthew, even if I have to buy slips again it's worth it if I get at about $15 worth of edibles for a $1 slip (based on my first harvest). You can't beat that for a return on investment!

Happy planting ya'll!

If you don't till and have a great diversity of soil organisms, you shouldn't have a problem with plant diseases like blight. Hypothetically, its just too hard for disease organisms to gain a foothold, because there is so much competition from bacteria, other fungi, protozoa, nematodes, etc.

Also, my wife picks the leaves of sweet potato and uses them in soups and other cooking.

Mathew,

Here in South Carolina and looking to try some perennial sweet potatoes next year. My gardening partner has some at her place and I'll see if she would leave some in the ground.
We'll see!
-Nate

@Nate - Excellent. I will look forward to hearing her results, if you can convince her to do so. Where in SC are you?

I just harvested about 6 sweet potatoes. What an amazing plant. It muscles through the hard-packed soil. This thread has been helpful, because now I started loosening the vines that had started to take hold in the garden. Hopefully it will lead to more potatoes at the root of each plant.

I'm interested in eating the leaves. Do you eat the leaves after you've harvested or can I eat them as the potato continues to grow? I'm concerned about taking away the plants ability to absorb sun/photosynthesize by plucking the leaves. BUT, I do have a ton of vines, so it shouldn't hurt to pick some, right?

OH, I just reread the thread and this part in particular....

And yes....eat the greens! They cook up bland and soft, comparable to spinach or chard. And keeping the vine tips pruned helps curb rampant growth where it might be unwelcome, and a moderate amount doesn't seem to harm the crop of roots....

Thanks, Alder!!

Hi Lisa here in Mount Pleasant, SC (near Charleston). Stumbled on this thread when i started planting sweet potatoes last year and had a great harvest, and am now hoping to salvage whatever is left in the ground over the winter.

I have been putting pinestraw, mulch (cotton burr, compost, etc) on top of where the plants/vines were and also some plastic on extremely cold nights.

just today i found 3 potatoes fairly close to the surface that i missed, and they look pretty good. I went ahead and dug them up and they are outside "sunning" as i type this. I will bring them in this evening where they will remain until i eat them It is supposed to go back down to like 28 tomorrow night, so i will put the plastic back down out there, but i was so pleasantly surprised to find these babies today (and still looking good).

Maybe one "burnt" (with cold) little spot on one. I don't know what they will look like or taste like when i eat them, but i'm a happy camper and am trying my best to "over-winter" them.

just wanted to say hello and will hopefully have a good report when the cold weather is all over with around here!!

Cheers,
Lisa