Growing Okinawan Purple Sweet Potatoes: A Beginner’s Guide
By: Michael D. Murphy
The first time I ever saw purple sweet potatoes was when my mother brought them home from her trip to Japan. She had grown up eating them back in New England, but she never ate any while living there because they were too expensive and hard to get in those days.
When she came back to Hawaii, she wanted to try something new. So one day, she went into the garden center and bought some purple sweet potatoes from a farmer named Kiyoshi. My mom didn’t really know what these things were all about at the time; it was just another way for her to save money on food! But after she grew a few of them, she decided that maybe she liked them better than regular sweet potatoes.
A couple years passed and my mom started bringing me to the farm every other week or so to eat purple sweet potatoes with her. I remember being fascinated by their appearance – they looked like little tiny red grapes!
They were delicious and tasted even better when dipped in butter or cream cheese. While there was nothing wrong with regular sweet potatoes, I felt that the purple ones had a unique taste and fun color to them. When we brought them home to my dad, he was not as fond of them. He couldn’t quite place his finger on what it was that he didn’t like about them, but he just couldn’t bring himself to like them. He much preferred the traditional orange-skinned sweet potatoes; even though he always complained that they gave him gas.
Kiyoshi’s farm was a fascinating place to visit. The rows and rows of different crops stretched out over several acres, and there were many people working there to maintain it all.
There were also fruit trees scattered throughout the property. One time, I remember seeing a big flock of parrots sitting in one of the trees. It was a strange sight. Kiyoshi was always a friendly guy and would talk about his family, the crops, and anything else that came to mind. He would usually offer us something to drink or snack on before we left. Once he even offered us some of his homemade wine! That was a crazy night.
In this post, I will discuss some of the main ideas about growing purple sweet potatoes, including its origins, types, and how to grow your own.
What are Purple Sweet Potatoes?
Sweet potatoes are one of the oldest vegetables known to man – some people even believe they originated in North America before making their way to East Asia. Today they are one of the most popular foods in many parts of the world, though they are not as popular in North America as other root vegetables like the carrot. They can be eaten on their own, roasted, fried, made into chips or fries, added to soups and stews, or mashed – the list goes on.
While there are several different types of sweet potatoes, purple sweet potatoes are most common in East Asian cuisine. These are native to China and Taiwan, though they also grow in other parts of Asia like Japan and Korea.
The skin of these sweet potatoes can range in color from a pale white or yellow to a deep red or purple. The flesh can also range in color, though it is usually a pale white or yellow.
Purple sweet potatoes are high in antioxidants and are an excellent source of vitamin C. They also contain a good amount of fiber, potassium, and iron.
How are Purple Sweet Potatoes Grown?
Purple sweet potatoes are typically grown in the ground, much like regular potatoes. They have large vines that spread out around the soil and occasionally climb up other vegetation. These vines can extend to great lengths.
Purple sweet potatoes are usually grown from their seeds, though they can be grown from pieces of their roots or vines as well.
The seeds of these sweet potatoes can be hard to find, though some garden stores and websites sell them. The seeds do not need to be planted in the ground as they can be placed in pots or other containers.
However, they do need plenty of water and sunlight to grow.
Purple sweet potatoes are susceptible to pests and diseases, so you’ll have to keep an eye out for those when growing your own.
What are Some Common Types of Purple Sweet Potatoes?
There are many different types of sweet potatoes, though the most common ones you’ll see in North American supermarkets are the ones sold as sweet potatoes and yams.
The regular sweet potato that you think of is bright orange on the inside and has a pale yellow skin. The yam is a darker orange color on the inside and has a brown skin.
Though the terms are often used interchangeably, yams actually belong to a different genus than sweet potatoes and are not part of the sweet potato family at all. True yams are not well-known or grown in North America.
There are several different types of sweet potatoes that you’ll find at your local market. One of these is the Okinawan sweet potato, sometimes also known as the purple sweet potato.
These can be found year-round and are often used for decorative purposes since their skin and flesh are an attractive purple color. They have a sweeter taste than other types of sweet potatoes.
How to Grow Purple Sweet Potatoes
While you can buy Okinawan sweet potatoes or similar varieties from the store, you can also grow your own. Growing your own gives you control over where the sweet potatoes come from, how they’re grown, and it can save you money.
Growing your own vegetables is also a rewarding experience.
Purple sweet potatoes grow the same way regular sweet potatoes do. You just need to take a couple extra steps to help your sweet potatoes have that signature purple look.
If you want your sweet potatoes to have that vibrant purple color, you’re going to need to keep the skins on the tubers. Most of the time, people are used to eating the flesh of the sweet potato and throwing away the skin.
However, the skin of the sweet potato is what contains that purple pigment.
If you peel the skin off, your potatoes will just be a regular orange color. Some varieties of purple sweet potatoes have lighter skin, so they won’t look as bad without the skin, but for the most part, they look dirty or diseased if you don’t keep the skins on.
You’ll need the following supplies to start your sweet potato plants:
Sweet potatoes (don’t wash them)
A sharp knife or shovel
Potting soil or garden soil
Container or garden bed
First, you’ll want to make sure you have a container or garden bed that will accommodate your sweet potatoes as they grow. You don’t want to plant them too deep, so you don’t want the tallest setting on your drill.
A depth of two inches is good.
Make sure the container or garden bed has had nothing in it that grows vines, as vine plants can wind around your sweet potatoes and give them a bad shape. Also, make sure your container or garden bed has good drainage.
You don’t want your sweet potatoes growing in standing water.
After you’ve chosen a spot for your sweet potatoes, you’ll need to prepare the soil. You can use either potting soil or regular garden soil, but you’ll want to mix in some compost as well to give the soil extra nutrients for your sweet potatoes.
After your container or garden bed has been prepared, you can begin planting. Planting instructions will differ depending on whether you’re planting one tuber or several, but the basic idea is the same.
You want to make sure your sweet potatoes have good contact with the soil, so you don’t want to plant them too deep. Most sweet potato varieties should be planted at a depth of two inches, but check the depth recommended for the particular variety that you’re growing.
Next, water the soil where you’ve planted the sweet potatoes. After that, keep the soil consistently moist, but not soggy.
You don’t want to overwater them, as this can cause the tubers to split. You also don’t want to underwater them, as this can cause them to rot and diseases to develop.
Insects and Wildlife
Most insects and wildlife won’t bother your sweet potatoes, but there are a few exceptions.
If you live in an area that has a lot of deer, rabbits, or rodents, you may want to surround your sweet potato patch with a lightweight fencing. This will help protect your sweet potatoes as they grow, and it will also give them a nice frame when they begin to flower.
You can also use repellents to discourage deer and other browsers from eating your sweet potatoes. Most commercially-available repellents are only effective for a short period of time, however, so you may need to reapply it every few days.
In most areas, you can harvest your sweet potatoes in September or October. Let the vines dry out and turn completely yellow before harvesting.
This indicates that the sweetness has developed fully.
Once you’ve harvested your sweet potatoes, cure them for at least a week or two in a well-ventilated, dry location that stays around 90ºF. This will allow the skins to thicken and the moisture to even out, which makes for better storage.
Once the curing process is finished, you can keep your sweet potatoes in a stable, cool location with plenty of ventilation and no rainfall.
Sweet potatoes are a nutritious, tasty, and relatively easy-to-grow crop that just about anyone can enjoy. Give them a try next fall, and see if you like them as much as I do!
Sources & references used in this article:
Anthocyanins in purple sweet potato (Ipomoea batatas L.) varieties by EC Montilla, S Hillebrand… – Fruit, Vegetable and Cereal …, 2011 – academia.edu
Characterization of anthocyanins and anthocyanidins in purple-fleshed sweetpotatoes by HPLC-DAD/ESI-MS/MS by VD Truong, N Deighton, RT Thompson… – Journal of agricultural …, 2010 – ACS Publications
Content of alpha-, beta-carotene, and dietary fiber in 18 sweetpotato varieties grown in Hawaii by AS Huang, L Tanudjaja, D Lum – Journal of Food Composition and Analysis, 1999 – Elsevier
Pressurized liquid extraction and quantification of anthocyanins in purple-fleshed sweet potato genotypes by VD Truong, Z Hu, RL Thompson, GC Yencho… – Journal of food …, 2012 – Elsevier