Okinawan Purple Sweet Potatoes are a lovely and delicious cultivar, featuring a creamy, beige skin encasing gorgeous purple-magenta flesh. Full of the antioxidant anthocyanin, they’re also high polyphenols, vitamin C, and soluble fiber. These sweet potatoes are easy for the backyard gardener to grow in the U.S. climate.
Hello, Blue Zones fans from the new Netflix series, welcome — I’m watching, too! I’m an avid follower of all things Blue Zones, and I hope you’ll find the information here about Okinawan Sweet Potatoes helpful.
In the U.S., they’re harvested Sept/Oct, but will probably be difficult to find anywhere but specialty stores and farmers’ markets. If you want to grow them in your backyard garden next year, you should be able to find slips — the starter plant – next March or April at the big online retailers (see info below).
Also, if you’re interested in the soup mentioned during the Sardinia segment, I have a recipe on my food blog for Sardinian Longevity Minestrone, which was inspired by one of the Blue Zones books.
What is an Okinawan Sweet Potato? What does it taste like?
Despite the geographic name famous for cultivating them, they’re also commonly grown in Hawaii and are often known as the Hawaiian Sweet Potato.
Okinawan Sweet Potatoes – a.k.a., Okinawan Purple Sweet Potatoes or Hawaiian Purple Sweet Potatoes – are a beautiful cultivar, featuring off-white or beige skin with a vibrant purple-pink interior. They’re starchy – more so than their orange-fleshed counterparts – but have no saturated fats or cholesterol.
They were, in fact, a dietary staple of the people in the famous Okinawa Blue Zone (an area designated as having a high number of centenarians).
They are, unfortunately, difficult to find in the typical American grocery store, which is a shame because they’re so delicious and are my very favorite variety of sweet potato.
Taste is subjective, of course, but I find them far less cloyingly sweet than the standard orange grocery store variety (often, Beauregard). Nutty and slightly earthy, they not only make excellent crispy fries, but are also quite lovely in salads (I’m an add-all-the-vegetables kind of green salad fan).
They cook up fairly quickly in a pressure cooker, and my favorite work-from-home vegetarian lunch is one topped with black beans, salsa, and guacamole.
Okinawan Sweet Potatoes retain their color when cooked and, in fact, deepen into a rich, dark purple, while the skins tend to take on the purple coloring.
What are Sweet Potato Slips and Where to Buy Them?
So, where do sweet potatoes come from anyway? Unlike most vegetables, sweet potatoes are not started from seed, but rather from mature shoots produced by the tubar, called slips. The shoots are removed from the potato once they leaf out, and then placed in water to develop roots.
You can definitely grow your own slips from a sweet potato, but if you don’t have a sweet potato in your possession right now, you’ll need to go ahead and purchase the slips from a reputable nursery for this growing season.
The slips will arrive carefully packaged, usually with the roots encased in a soil plug. You should remove the slips from the outer packaging immediately upon receipt, leaving the root plugs intact.
It’s important to note that sweet potato slips are not cold-weather hardy. This presents a challenge to the gardener: you either lock in your order as soon as you find them (whether you’re ready to plant or not), or you wait to order until the weather is perfect and risk everyone being out-of-stock.
For me, the decision is easy: I want my Okinawan sweet potatoes, lol, so I don’t take a chance. I order early. This year (2021), mine arrived a full month before they’ll be planted, as we’re still having floods and the occasional overnight dip into the 30°Fs here in March and April.
A Note for the 2024 Growing Season:
I’m having a heck of a time finding Okinawan potato slips this year. Sweet potato slips are usually available for pre-order now or purchase in March or April. For years, I’ve bought from Baker Creek Seeds, but they don’t seem to carry them this year. In fact, their sweet potato inventory is shockingly small. I’ve found listings on Etsy and Amazon, but you’ll need to understand the risk of buying from random growers who might be inexperienced at growing, nourishing, and shipping slips. I’ve found a few retail sources for the purple potatoes mentioned in the Netflix special (purple skin and purple flesh), including Johnny’s Seeds and a new variety at Baker Creek. Also consider growing Murasaki potatoes, which are a magenta-skinned, white-fleshed Japanese potato that are quite delicious.
Update: A kind reader wrote to let me know that they found Okinawan Potato slips for sale at George’s Plant Farm. I don’t have personal experience with this grower, but they have an amazing inventory of sweet potatoes. Worth a look!
Update mid-April 2024: It looks like George’s Plant Farm has sold out of the Okinawan Potato slips! It’s late in the buying season now, but still not too late: I would go for the Purple Passion or the Red Japanese. The folks there have no idea who I am, and I’m not getting a commission; I’m just so excited to see a grower offer such a beautiful variety of sweet potatoes. A farm after my own heart!
I used to purchase my slips from Baker Creek Seeds. I’d hit their Live Plants page early in March, and sign up for the back-in-stock notification. As soon as I get word that they’re ready to purchase, I pounce, no matter the date or weather forecast. In 2024, however, I didn’t have any luck getting varieties I was interested in.
Once the slips arrive, I keep them in their little plastic shipping bags, rolled down to expose the upper leaves for aeration, sitting firmly in a ramekin in a morning-sunny window until I’m ready to plant. Keep the soil plugs lightly watered, and the slips will thrive. This year’s slips:
When to Plant the Slips
Your slips will be ready to plant when temperatures in your area no longer dip into the lower 50°Fs. For my Zone 6a, that’s mid- to late-May. In 2020, I planted my sweet potatoes on May 17th; May 15th in 2021 (although we went on to have a freakish dip into the 30s late in May, and I had to cover the plants to protect them from frost).
But don’t go just by the calendar; let nature be your guide. If it’s still snowing after your last frost date, don’t take a chance (look up your last frost date in the U.S.).
If you received them early and have been caring for them inside, first harden them off a bit by letting them spend a few hours outdoors each day for a week, under gentle sunlight (say, morning hours), before planting. If you don’t have a safe space for this (e.g., if you live in an apartment and are planting in a community garden), place the slips by an open window.
Prepare the soil
Sweet potatoes are not terribly fussy and are, in fact, robust survivors. But, the goal of this effort is to produce beautiful, well-formed sweet potatoes, and proper soil prep will take you a long way. The potatoes form underground, so the composition of the soil is everything.
At least one week before planting, you’ll want to deeply turn the soil where you’ll be planting the slips. This central planting is often called the “crown,” and that’s how I’ll refer to it in this article.
Then, at least lightly turn the soil in a 10-foot radius in every direction: vines will drop roots at their leaf notes to secure the plant to the ground as it expands. And sometimes, if you’re lucky, the plant will produce another cluster of potatoes from the nodes, so turning the entire bed deeply would not necessarily be a wasted effort.
Amend the soil throughout the bed with compost. Smooth out the top with a rake, water lightly, and let rest.
Clay soil is not optimal for potato formation because it’s not pliable enough to allow the potatoes to form naturally. It’s not impossible, but you’ll need to add a lot of compost to the crown area to lighten the soil.
At the other end of the soil spectrum, loose, very peat-y soil is also not the best for potato formation. Potatoes need a little resistance – a guiding hand, if you will – from the soil to keep from growing too long and skinny, or to become malformed in a way that’s awkward for cooking.
The ideal soil is light and “fluffy”, but holds together well when damp and squeezed. The area should also be well-draining, as sweet potatoes like to be damp, but not drenched. Do the hole test: dig a hole 12″ deep and fill it halfway with water. The water should drain away in the soil at a fairly fast clip. Standing water indicates that the bed needs to be turned more deeply and amended with compost.
How Much Space is Needed to Grow Sweet Potatoes?
I won’t mince words here: you’ll want a big space!
Although the actual clusters of sweet potatoes do not take up too much two-dimensional area – in fact, you can absolutely grow them in a large burlap bag or container – they require nutrition from the leaves that the plant’s vines produce. And those vines grow incredibly long.
So, actual in-the-ground space needed by the potatoes: small’ish. Actual spread space needed for the vines: large.
I grow all of my sweet potatoes in a 10-foot x 10-foot plot. This plot is too small, lol, but it all works out: as the vines reach the fenced boundaries, I begin redirecting them to wrap around the plot’s edges in a circle.
Note that you can grow other plants in the same plot: anything that grows tall, whose own leaves will be well above the leaves of the sweet potato vines. Keep in mind, though, that late in the season, the area will be very densely covered in vines and leaves and will be difficult to reach. You could, however, plant something like bell peppers along the border of the plot, where you’ll easily be able to reach the peppers without squooshing the sweet potato vines by walking on them.
Last year, I grew honeynut squash in the sweet potato bed, and even though there were vines e.v.e.r.y.w.h.e.r.e, it all worked out rather well, and both harvests were quite abundant.
How to Plant Okinawan Sweet Potatoes
You’ll want to plant the slips 12 to 18″ apart, so that the potatoes have plenty of room underground to sprout, separately from each other. They don’t have to be in rows.
As you saw from my plot illustration above, I plant three slips in a little triangle, with the varieties separated from each other with additional space.
Pluck off the lower leaves of the slip, leaving an umbrella of leaves on top.
Dig a hole 4″ deep and set the slip firmly all the way in, pressing the soil firmly against the plant. Water well.
Finally, you’ll want to mark the crowns – the base of the center plant. The majority of sweet potatoes will be produced in a cluster beneath the crown. Sounds simple enough, right?
But in a good year, healthy plants will produce an abundance of leaves from numerous vines shooting out in every direction, filling the surrounding space with gorgeous greenery and obscuring the location of the crown as the season wears on.
I always drive in a 3-foot stake near each crown, so that in October, I know exactly where the concentration of sweet potatoes will be located.
Caring for Okinawan Sweet Potato Plants
One of my favorite things about growing sweet potatoes is that they’re very easy to care for and are basically hands-off for much of the growing season.
After the plants have acclimated to their new soil home (two to three weeks), I fertilize once every two weeks early in the season, but as soon as the vines are robust and leafy, I halt fertilizing altogether, unless we’ve had a lot of rain.
Regular fertilizer with a formula of 5-10-10 or 8-24-24 is just fine, keeping an eye on the nitrogen. Even though sweet potatoes need their leaves for nutrition, you still don’t want to encourage the plant to go completely overboard with the greenery by overfeeding it with a too-heavy nitrogen concentration. This would produce too many leaves and not enough tubars.
Protect the leaves!
Do deer eat sweet potato vines? Oh, yes, they do! Furry woodland creatures love sweet potato leaves — they’re edible to humans, too — so plant your sweet potato slips in a fenced-in plot, protected both from deer and bunnies.
Remember that deer can jump very impressive heights, so my fencing is 7 feet tall, with chicken wire wrapped around the lower 2 feet, sunk a bit into the ground, to keep out the hungry bunnies.
However, if your sweet potato vines do get stripped of their leaves by a clever rascal, don’t give up. Sweet potatoes are determined survivors and will usually leaf out again fairly quickly.
Because the plot I use for my sweet potatoes is fairly small in proportion to the plant size, a few of the vines inevitably escape through the chicken wire and grow from there. I consider anything outside the fencing to be fair game for the furries. 😉
There is one distinct advantage to sharing the area with sweet potato leaf-lovin’ creatures, though: at the end of the growing season, about a week or so before my planned harvest, I remove all of the fencing, and let everyone have at it.
This clears the area of leaves and reveals the sweet potato vines. It also makes digging so much easier, because I’m not struggling to get through the thick bed of leaves to find the ground in which to dig.
I hope you’ve found this article helpful! Growing Okinawan sweet potatoes is a low-hassle joy, and the resulting potatoes are absolutely delightful and worth the space they occupy in the garden.
If your crop is ready to harvest, I’ve got your back with this guide for how to harvest and cure sweet potatoes.
Happy Planting!
I hope you found this post helpful, and that it inspires you to grow your own edibles at home, expand your garden repertoire, or try a new technique. If you have any questions or comments, please share them below so that everyone can benefit from your thoughts, advice, and curiosities. Use the buttons above to share this information on your favorite social platform.
Welcome! I'm Karen, Chief Gardener, Tool Cleaner, Tomato Pruner, and Cabbage Worm Picker-Offer.
This article has a wealth of info and clearly written descriptions. Just what I had hoped to find. Thank you!
I planted 3 Okinawa Purple Sweet potato slips from Baker Creek in a 100 gallon grow bag. It took many weeks before they started to grow new leaves I’m told to expect to harvest starting right about now but the plants never took off. Not much in the way of vines and leaves. I’m debating just waiting until the vines do start growing like crazy. I’m in 10a so I don’t have a Fall / Winter looming that’ll cut off the growing season.
Is there a way to know when there are tubers under there? It’s such a mystery! And I’ve seen enough #fail sweet potato YouTubes to be nervous.
It’s a complete mystery, lol. I do have distinct seasons here, and a hard stop with the first deep frost, but I usually just go for it in mid-October.
The leaves and vines do not provide any clue as to what’s going on beneath the ground, unfortunately. You could carefully dig into the container with your hand or something else that’s not sharp (you don’t want to pierce any potatoes that might be growing) and see what you can feel.
Without an abundance of leaves and vines, I would expect, at most, clusters of small potatoes. But I would definitely let them go well into October. Maybe give the container a boost of fertilizer and see what happens. Crossing fingers for you!
I’m in zone 9 and last year I got pretty lazy and didn’t dig up the sweet potatoes until the second week of November. What a nice surprise! I’m glad I procrastinated! The potatoes were large and healthy. I also planted a lot fewer slips in the bed, so the few slips that were there had all of the nutrients from the soil without competition (btw….the bed is 4’x7′ and I planted 40 slips to the bed).
Hope this helps!
Once picked from garden should I let the potato “dry” out before cooking?
Technically, they’re ready to cook now, no problem! But if you have a harvest that you want to last for a while, they’ll need to be cured first. I let my potatoes cure for several weeks in a cool, dry location. My unfinished basement is perfect for this. There’s nothing special to do – just let sit in the open, with the dirt still on them.
Dear Karen:
Thanks for this excellent article you wrote about how to plant Okinawan sweet potatoes, my favorite. They are more than $3 /Lb nowadays. I am on low budget, tried to grow slips from a few tubers bought at grocery store for longer than 3 months but failed. Nothing happened. sad. Will try again next year. Luckily grow some slips out of Murasaki that I bought at TJ. This will be the first time for me to grow sp.
I live in zone 8, water is not cheap here. My question is: when we water the plant, do we just water on about 1 square foot area where each crowns are, or water the whole few square yards where the vines reach? Looking forward to your kind reply. Thanks in advance.
Hi Marcy,
I can sympathize! Produce is so expensive, and it’s pretty economical to grow sweet potatoes because they don’t require equipment (such as stakes or trellises). When I water my sweet potatoes, I only water the crown. But I do get decent rain throughout the summer, so the small rooting nodes that the vines drop along their length get enough moisture from rain alone. If you live in a dry zone, you might want to water along the vines every once in while, but mostly concentrate on the two or three feet around the crown. I hope that helps. Best of luck with your sweet potatoes!
Approximately how many potatoes does each slip yield?
As a really rough estimate, I would say 8 to 15. But there are so many factors, including soil, growing conditions, whether any of the vines take root beyond the crown. I’ve gotten anywhere from zero to 30.
I am in zone 6B (possibly 6A depending on the year) South of the STL MO area. We just moved to a new house and I have vines just all over the place and google identifies the vine as Japanese Sweet Potato. I am anxious to dig there in the next couple of weeks to see if it might be a GOLD patch!!! we will see. I guess I am wondering will this keep coming back every year? Do I need to do anything to “winterize” or anything? I heard we are to have a mild winter this year so possible that I don’t need to do anything this year but for a normal or colder than normal winter would I need to do anything or just make sure to leave tubers in the ground?
where can I buy organically grown Japanese sweet potatoes? I hear the non-organic potatoes are sprayed with an inhibitor to prevent them from giving off shoots.
If you purchase slips from legit growers – as opposed at the grocery store – they’ll be properly raised to produce potatoes. But, you’re right, a lot of grocery store produce is treated with inhibitors so they don’t start sprouting in the produce bin. Many seed catalogers sell a variety of sweet potatoes. This is the perfect time to be searching for them, as growers are producing slips in prep for March or April shipping. I’m on the hunt myself!
I found slips that can be sent when you request at
tatorman.com 2024
Thanks for sharing the info (and for your message because the comment ended in spam because of the link)!
Hello,
I’m in Western Canada and I would like to acquire some Okinawan tubers to start this year. Any ideas where I may purchase good quality ones? I need to be sure they are a product that will pass border inspections!
Thanks,
Jim
I’ll be sure to update here if I find Canada—friendly sources!
Hi! I am not sure if I am able to plant in ground and just ordered 25 are these a vegetable that doesn’t do well in large mineral tub sized pots? Should I try to figure out a way to plant them in the ground instead? Thanks!
Hi there,
I personally don’t have any context for how large a mineral tub is (Google wasn’t really any help), but in general, yes, you can absolutely grow sweet potatoes in containers. Just make sure that each plant has enough room under the soil to accommodate a cluster of mature sweet potatoes (envision how much space that 5 or 6 sweet potatoes occupy; say, 2 feet deep, 2 feet in diameter), and also that the plant’s vines have room to grow and trail over the edge of the container and then over ground — they grow quite long! (the leaves nourish the potatoes). With 25, it’s probable that you’ll need multiple containers, but again, I don’t know what a mineral tub looks like. Also make sure that there are drainage holes to promote proper drainage, as sweet potatoes don’t like wet feet.
Wishing you an abundant harvest!
Whole Foods now carries several of the more fun varieties of sweet potatoes, and it’s easy to sprout your own by having them and setting them into soil indoors or water. Gently break off the sprouts, put in water, and in 3 days, ROOTS!
I got Japanese purple, Stokes Red, and “red” Sweet potatoes. Japanese sprouted fastest.
That is awesome news! I haven’t been to WF in a while — I’m definitely going to have to check them out. Thanks for writing!
I can’t be certain mine are this type, but the leaves on the mature vine look the same, and the root I planted to start them looked the same. Problem is, the tubers from its runners’ roots (which is what the commercial slips must be) come out mostly white with streaks of purple, or all white. Our soil has a lot of limestone, which reduces acidity, and is low in phosphorus. Do you think either of those be a cause? Any ideas of how to get the beautiful purple back?
Hello! I have visited and re-visited your article often! Thank you so much for anif this wonderful information! I live in southwest Virginia and I ordered slips for Beni Imo this year. I planted them in May. The plantings are thriving (going crazy actually!) but I am concerned if they are actually Beni Imo. The leaves look like hearts and they are planted in a raised bed with chicken wire gates. They have filled the 10×10 box and are now growing through & up the gates. There is a beautiful purple flower (looks like a morning glory) growing up the gates also. Can you tell me if that sounds like the Beni Imo variety or something else? Thanks!
Oohh, what a rare treat! Sweet potatoes don’t often bloom but if I were you, I would enjoy the show and keep on growing’!
Sweet potato flowers are usually purple or pink and trumpet shaped. If this applies to your plants, I’d say it’s a good chance that all is well!
Thanks for the article. Very informative. This year I planted Diana and Okinawan and like for the last few years in Miami and now in Tennessee I buy my slips from George Farm, they are very reliable and honest and serious and they are located right here in TN.
Thanks again.
Hi, thank you for the article.
I try first time to grow sweet potatoes in Bretagne (France) at the west coast. I bought slips from a French farmer of a purple flesh variety. I planted them in beginning of June and we had so much rain in June, that I didn’t bother watering.
Now it is mid September and the green of the plants is all over the garden.
I have a problem, because a mole is digging around my garden since a couple of days and I’m afraid it could ruin my tubers. So I hesitate, should I dig them out before the mole does an risk to harvest too early? Or should I wait till October and risk the mole to destroy everything?
Please advise me quickly, before I panic.
It is early October here in zone 8a and I have a 12 by 18 bed of thickly growing Okinawan Purple Sweet Potatoes. Is it possible (or practical) to root shoots indoors for online sales in March? I’m thinking that they will get too long.