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.
Japanese sweet potatoes, also known as satsumaimo, are a tasty and nutritious vegetable that are fun and easy to grow at home With just a little effort, you can have a plentiful harvest of these unique purple-skinned, white-fleshed tubers Here’s a complete guide to planting and caring for Japanese sweet potatoes in your garden.
Japanese sweet potatoes are native to Japan and have been cultivated there for centuries. They are different from the orange-fleshed sweet potatoes commonly found in American grocery stores Some key facts about Japanese sweet potatoes
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They have a thin, smooth, purple skin and a creamy white flesh. The skin color can range from lavender to deep purple.
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Their taste is drier and nuttier than orange sweet potatoes. Less sweet and more starchy.
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They are packed with nutrients like vitamin C, vitamin B6, antioxidants, and dietary fiber.
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In Japan they are known as satsumaimo and are often used in simmered dishes, tempura, or baked goods.
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They are easy to grow in warmer climates and produce high yields.
When and Where to Plant
Japanese sweet potatoes need full sun and warm soil to thrive. Here are some tips on timing and location:
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Plant sweet potato slips or cuttings 2-3 weeks after the last expected frost date for your region. Avoid planting if temperatures may dip below 55°F.
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Choose a sunny spot in your garden that gets at least 6 hours of direct sunlight per day. More sun equals higher yields.
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Make sure the soil is loosened 12+ inches deep and drains well. Amend clay soil with compost to improve drainage.
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Extend the growing season by planting a second crop in mid to late summer for an autumn harvest.
How to Plant Sweet Potato Slips
Sweet potatoes are grown from slips, which are sprouts that form on mature sweet potatoes. Here’s how to plant slips:
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Purchase certified disease-free slips from a reputable source. Look for strong plants about 8-10 inches tall.
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Remove any leaves or vines from the bottom 3 inches of the slip.
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Plant slips 12-18 inches apart in rows, burying them 3-4 inches deep in the soil.
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Water the slips well and keep the soil consistently moist (but not soggy) while plants become established.
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Apply a balanced organic fertilizer when planting and every 3-4 weeks during the growing season.
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Place a plastic mulch over the planting row to increase soil warmth and reduce weeds.
Caring for Your Sweet Potato Plants
With good care, your sweet potato plants will thrive. Follow these tips for healthy, productive vines:
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Water plants 1-2 inches per week if rainfall is insufficient, more in very hot weather.
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Weed around plants to reduce competition for nutrients and water.
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Apply an organic fertilizer monthly to fuel plant growth.
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Remove any vines that root along the row to prevent misshapen potatoes.
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Hill soil over the plant crowns during the season to encourage more potato growth.
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Avoid wetting the leaves when watering to prevent disease issues.
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Monitor for common pests like aphids, wireworms, grubs and flea beetles.
Harvesting Your Sweet Potatoes
Sweet potatoes take 90-120 days to reach maturity. Here’s how to harvest for the biggest, healthiest tubers:
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Time your harvest before a hard frost, which damages the potatoes.
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Stop watering about 1 week before you plan to harvest.
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Dig carefully around each plant with a shovel or garden fork, taking care not to pierce the potatoes.
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Gently lift out the potatoes and remove excess dirt by lightly brushing or hosing them off.
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Cure harvested potatoes for 4-7 days in a warm, humid location out of direct sunlight before long-term storage. This helps thicken skins and seal wounds.
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Store cured sweet potatoes in a cool, dry place around 55°F for 2-3 months. Avoid refrigeration, which converts starches to sugars and alters the flavor.
Troubleshooting Common Issues
Follow these tips to overcome potential problems while growing sweet potatoes:
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Poor germination of slips may be due to old, damaged plants or incorrect planting depth.
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Slow plant growth can be caused by cool soil, excessive rain, compacted soil, or nutrient deficiencies.
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An absence of potatoes may result from inadequate sunlight, poor drainage, or underdeveloped vines.
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Misshapen potatoes are often caused by shallow planting depth, soil compaction, overwatering, or growing in heavy clay.
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Rotted potatoes can be avoided by planting in well-draining soil, rotating crops, and watering at the base of plants rather than wetting vines and leaves.
Enjoy Your Bountiful Harvest
With the proper care, you can harvest mounds of scrumptious Japanese sweet potatoes. They can be roasted, mashed, fried, or used in soups and other dishes. Their sweet, mild taste and unique purple skin make them a fun alternative to standard sweet potatoes. So try growing Japanese sweet potatoes this season for a distinctive addition to your garden and kitchen!
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:
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.
How To Grow Japanese Sweet Potatoes (Satsuma-Imo) | Doctor of the Future 007
FAQ
Which way do I plant a sweet potato?
Plant your sweet potatoes by sinking the sprout to about half its length, and water well before firming the soil. The first step toward a bountiful sweet potato crop is getting the soil right. A moderately fertile, sandy loam is best.
What month should you plant sweet potatoes?
The best time to plant sweet potato plants is after the ground is thawed and after the last spring frost date has passed. If the ground doesn’t freeze in your location, then the best time to plant is usually a month after your last spring frost date.
How long do Japanese purple sweet potatoes take to grow?
Of note, the plant requires a long and hot growing season – it may take from 120-180 days from planting to harvest. It needs full sun (at least 6 hours a day) and well-draining soil that is (ideally) slightly acidic (pH from 5.5-6.5).
Can I plant sweet potato slips directly in soil?
Yes, sweet potato slips can be planted directly into the soil. It’s a common practice to start slips by rooting them in water first, but they can also be planted directly into the ground or a container filled with soil.