Your sweet potato questions: Answered!

Last week, I asked y’all to share your questions about growing sweet potatoes. And, you did! Thank you! Now, let’s see if I can answer them all for you.

[Note: If you are just joining us, you might also want to check out my posts about last year's sweet potato harvest and starting your own sweet potato plants from store-bought tubers.]

Some of you asked for more details about growing your own sweet potato slips:

Is it easy to find organic sweet potatoes to start growing? The S.P. one finds in the store do they have to be labeled “organic” if they are?

Yes, look for sweet potatoes that are labeled “organic.” Non-organic sweets are often treated with a sprout-supressing chemical, and we want these sweets to sprout! As for ease of finding them, it all depends on where you live and what sort of stores you have. Around here (rural northern Virginia) organic sweets are pretty easy to come by. Most every grocery store sells them.

One thing to keep in mind: Avoid organic sweets that are shrink-wrapped in plastic. Sweet potato roots are alive, and I suspect that plastic wrapping might suffocate them.

I just read another article that said to bury whole sweet potatoes in few inches of soil in containers indoors and wait for them to sprout. I started some in water last night, but I’m just curious whether you’ve tried this method and if one method is better than the other.

I haven’t tried starting sweet potatoes in soil or moist sand, but I know that’s what some people do. The most important thing is to be sure your sprouting sweet potatoes have ready access to moisture.

Is it too late this year to start this? How long until I can harvest?

Depending on where you live, you probably still have time to start some sweet potatoes this year. It takes about 4 weeks to grow your slips. Then, once you transplant them outside, they will want another 100-140 days to produce harvestable tubers. If you wait until right before your first frost, you will guarantee that you harvest the biggest tubers possible.

I got the organic sweet potatoes and did as you said in the blog, however my dish and the 2 halves have started to grow mold. I pulled it out from the direct sunlight but am wondering what I should do differently to grow slips not mold???

I tried this method, but the mother sweet potato turned to mush within 4-5 days. It was a firm sweet potato when I cut it half and put it in the water. Do you have any suggestions or thoughts?

I am so sorry to hear this! I’ve never had trouble starting sweets this way, but that doesn’t mean it’ll work every time for every person. I’m wondering if you may have started with an unhealthy tuber. Sweet potato tubers are alive, which means they need to stay warm and be able to breathe. I know some stores sell their organic sweets in plastic wrap. I wonder if that suffocates the tuber? Also, if the tuber was ever stored below 50°F, that could certainly injure or kill the root. Either way, if you start with a not-alive sweet potato, it definitely won’t grow.

I hope you tried again!

You said container (with cut potatoes) needs to be set near a window….does it need to receive lots of sunshine at this phrase? The window in my kitchen faces east, and I am planning to place the container at a shelf next to the window….would it work? Or do I need to place the container on the bank of the window?

The tubers don’t need sunlight at all. It’s the growing slips that want light. Indirect light will certainly work, but the slips will grow faster and larger if you can give them direct, full light.

I have my cut SPs sitting next to my window right now (day three) in an east facing window which is facing a covered patio so no direct sunlight. I am in the high desert in CA and daytime temps are around 80-90, night temps in the high 40s to low 50s. I have a greenhouse that gets direct sun most of the day and am wondering if I should put them in there to sprout or is that too much sun and heat for them right now?

I’ve always started my sweets at about 70°F, because that’s roughly the temperature of my kitchen (and, somehow, sweet potato slips always end up being a kitchen counter project). So, I’m not totally sure how they’d do with temperatures in the 90s. But, sweet potatoes are a tropical vine, native to Central or South America. That makes me suspect your sweets will do just fine in the greenhouse. Just be sure they stay nice and moist!

How many plants come from a half a sweet potato? 

A single healthy sweet potato will often produce a dozen or more slips. So, a half a potato should give you at least 6 slips, and I wouldn’t be surprised if you ended up with more than that. Healthy sweet potatoes are very enthusiastic about producing slips.

What size container would be good for the slips?

It all depends on how many slips you want. A single sweet potato will generally give you about 12 slips, and will fit nicely in a large bowl. If you want more slips, I’d suggest starting them in a casserole dish. But, really, any watertight container with a flat bottom will work.

Once the slips are ready to be transplanted, you can either plant them directly into the garden (assuming the timing / temperatures are right) or pot them up to a four-inch pot (or larger, if you like). They can’t stay in a four-inch pot for too long, but a few weeks will be fine. Then, just move the outdoors to their forever homes.

Others asked about how to plant the slips into the garden, and what sort of care the growing plants would want:

How many slips do you plant in those bushel baskets?

I’d suggest just one slip per bushel basket. I did plant several baskets with two slips last year, but didn’t notice any real difference in the harvest. So, if you want to maximize your harvest, it seems worth it to plant only one sweet potato in each basket.

Any tips on how to care for them once they’re planted outside? How much water do they need? Should they be planted in a super sunny spot, or part shade? I love this, and want to start some today!

Sweet potatoes want full sun. They will do ok in part-shade, but they will probably produce less than full-sun plants (this is what I noticed in my garden last summer). As for care, sweets are pretty undemanding. They want loose soil that has been amended with compost (so, no different than most garden plants), and then shouldn’t need any more “food” for the rest of the season. Only fertilize if the plants look unhealthy; too much nitrogen can result in beautiful, leafy plants and teeny, tiny tubers. Watering needs follow the same pattern — these are not thirsty plants, and can handle moderate drought. The only times to really worry about water is when you first transplant your slips, and when the plants begin forming tubers (about 60 or so days after you transplant the slips).

Temperature is another story, however. Sweet potatoes won’t tolerate cold. It’s best to resist transplanting them into the garden until after nighttime temperatures are reliably at 50°F or higher. Temperatures below 50°F can chill and damage the plants.

In Hawaii, we have purple sweet potatoes. They’re a beautiful violet color on the inside, and a little dryer than regular sweet potatoes. Have you ever seen one?

Two people asked about purple sweet potatoes and/or purple-leaved sweet potatoes. I’m not familiar with either, but there are an incredible number of sweet potato varieties out there. If you want to try growing a more unusual variety, I suggest looking into nurseries and seed catalogs that specialize in heirloom or rare plants. You will need to start with purchased slips at first, but you can grow your own slips from saved tubers in future years.

[Note: I'm sticking with my store-bought sweets this year, but am hoping to experiment with some heirloom varieties next year. So, if anyone knows of a wonderful and obscure sweet potato variety, please let us know what it is and where you found it. Thank you!]

Do sweet potatoes grow in South Florida?

Any chance these sweet potatoes can make it in the heat of Tucson, AZ???

I live in Western WA (across the Sound from Seattle) and it’s pretty cold here. I think our average temp for summer is in the 60′s. It’s May 3 and it was barely 40 degrees this morning. Should I even bother trying these? We have a short summer and it doesn’t get very hot.

Sweet potatoes love heat, so I imagine Florida and Arizona would both work fine. As for cooler regions, you can still grow sweets, but you may need to help them along. Mother Earth News has a terrific summary of ways to coax along sweet potatoes in cooler regions: Grow Sweet Potatoes — Even in the North. Gardeners in short-summer regions might also want to select sweet potato varieties that mature in 100 days or less, such as Georgia Jet or Beauregard.

Can you train vining sweet potatoes up string /trellis to shade a window?? Double duty is needed on the West side of our home…

Honestly, I’m not sure… Sweet potato vines do not grab onto things like beans or peas or cucumbers do. So, if you grew them on a trellis, you’d need to tie or train them. And, some varieties produce relatively short vines. So, maybe not the best choice for your trellis spot. Why not try some tomatoes or pole beans at the window, and then grow the sweets where they can ramble on the ground?

I have a container patio. Can I grow them there? What size container? Do they need or would they benefit from a trellis?

I was under the impression that s.p. needed lots of room but if I can grow them in a bushel basket then great! Could you please let me know the size of the basket you are using? How many did you put in there?

Absolutely! I love how sweet potatoes look in containers, and it makes the harvest super easy. Last year, I grew sweet potatoes in bushel baskets, but any large container would work. I think you’d want to allow at least 18 x 18 x 18 inches (or thereabouts) for each plant. So, one plant in a bushel basket. But, several plants in a whiskey barrel.

Do you add additional soil as the vine grows to increase the depth for potato growth? I was successful with fingerling and red potatoes last year using haybale method would this work too for sweets?

Great question! Quick answer: no need to bury the sweets. Sweet potatoes and potato potatoes are not related, and grow differently. Regular potatoes (like your fingerlings) produce roots are each buried leaf node, which is why we cover them as they grow. Sweet potatoes will also produce roots at leaf nodes, but my understanding is that those secondary roots don’t produce large tubers.

As for the haybale method… Did you use haybales to create a raised bed for your potatoes? If that’s the case, then I imagine it would would great for sweets too.

Can they be companion planted near tomatoes? I have a very limited garden space.

My trusty Vegetable Gardener’s Bible says that sweet potatoes are good companions for marigolds, and bad companions for beets, carrots and potatoes. Makes sense, since those plants would be competing for underground growing space. No mention of tomatoes. And, likewise, the tomato entry makes no mention of sweet potatoes. So, perhaps it’s worth a shot?

My only concern would be that you will be harvesting those sweet potatoes by digging up the soil near your tomatoes. Now, that might not be an issue, since sweet potatoes aren’t harvested until right before the first frost. But, it’s something to think about…

Or, you could put a container of sweet potatoes at the base of your tomato plant. No risk of harming the tomatoes when harvest time rolls around, because your sweet potatoes will all be in the container, and not in the ground.

Also, if space is an issue, you might try one of the more compact sweet potato varieties. Bush Porto Rico, for example.

And, a few of you are already thinking ahead to harvest time!

From each plant, how many potatoes can I expect? I am excited to try this and look forward to your responses as well as future posts on the topic!

Last year, my healthiest plant gave me five large tubers and several smaller ones. All the other plants (which were partly shaded in the afternoons) gave me about 3-4 big tubers and several smaller ones. I’m thinking my harvest would have been larger if I’d started the sweets earlier (I didn’t get them going until late June last year, because I was literally creating the garden as I was planting it). So, I think 3-5 tubers from each plant is reasonable, and you might do MUCH better than that.

Do you have to crop the top and let them set for 2 weeks like in a garden and all that jazz?

Sweet potatoes do need to cure before storage, yes. And, although you can eat them right away, they actually taste better after a couple months of storage. So, curing is an important step. Curing is simple: the roots want to be kept at about 80-90 degrees for a few days after you’ve dug them up. This causes the tuber to form a thick skin, which helps ensure the tuber will store nicely for many months.

I haven’t perfected my curing technique yet, so I’d love to hear how others do this. I’ll be experimenting with this when the time comes. In the meantime, if you want to learn more, I suggest checking out the Mother Earth News article, which explains the how and why of curing and storage.

I read somewhere that after the sweet potatoes are harvested, you must store them in a cold cellar for several months. Any comment about this?

Well, yes and no. I’ve read that sweet potatoes become sweeter with storage, and I definitely found that with my sweets last year. But, a root cellar isn’t necessary. In fact, a root cellar might make them pout. These are tropical plants, and they don’t like to be below 50°F, or thereabouts. I just stored mine in an open bin on the kitchen counter. I still have one or two left from last fall’s harvest.

 Finally, here’s some advice that one reader shared:

“…a little trick that is used in planting sweets is to dig a trench and fill with a mixture of sand and potting mix or some compost then mound up the remaining dirt so that there is a ridge and then plant on top and the sweets have a material to expand in. Works great. I have just planted mine, and I live in eastern Kansas.”

Anything else you’d like to know that’s not already here? Just ask! And, please, if you have tips of your own to share, please post them in the comments section. Thank you!

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Tagged as: container gardening, faq, frugal, growing guide, sweet potatoes