Plant of the month: Uala sweet potato perfect for growing in Hawaii

  • The open flower of the ‘uala has a lovely five point star outlined in its petal. (uga.edu/Courtesy Photo)
  • The purple ‘uala is often used to color and flavor pies and cakes. (ktasuperstores.com/Courtesy Photo)
  • The ‘Margarita’ variety of ‘uala has light green heart shaped leaves. (epicgardening.com/Courtesy Photo)
  • The ‘uala has attractive palmate leaves and a lovely white and purple flower. (cookislands.bishopmuseum.org/Courtesy Photo)

The plant known as the Hawaiian sweet potato is not native to Hawaii. Although the plant has the Hawaiian name uala and its tuber has been a staple in the Hawaiian diet for centuries, it is actually native to parts of South America. Though it is not known how or when it arrived in Polynesia and Hawaii, the Hawaiians were cultivating it here when Captain Cook arrived in 1778.

The plant is perfectly suited to our Kona climate and can be an attractive as well as a tasty addition to local gardens. It can tolerate full hot sun as well as partial shade and can go a while with limited water, fertilizer or maintenance. And, it produces delicious tubers as well as tasty shoots that can be harvested and eaten. Uala has it all!

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Known botanically as Ipomea batatas, uala is a member of the Convolvulaceae or morning glory family. Its growth habit and flowers are somewhat similar to morning glories, although it is not nearly as invasive. Like its cousin, uala has a viney growth habit. It usually stays close to the ground, however, and rarely climbs. Several different varieties of the sweet potato plant are grown here. They are distinguished by the color and shape of their leaves and their tubers.

The “blackie” cultivar has leaves that are very dark green, almost black. The leaves are palmate in shape with deep lobes. Another common cultivar is “margarita.” Her leaves are usually a light green and more heart shaped. Interplanting the two contrasting cultivars can add a dramatic touch to your garden. Both put out shoots that can grow long fairly quickly. In a short time the plants will grow to 4 to 6 inches tall and can cover a lot of ground.

The flowers of the uala plants are lovely, though they appear infrequently. Usually they are white or light lavender funnel-shaped blossoms with deep purple centers. When the flower is fully open a five pointed star is visible in the folds of its surface adding to its charm. The flowers do produce seeds but the best propagation technique is by shoot cuttings.

The uala plant that commonly grows here produces tubers that are often light brown with purple meat. Some cultivars produce tubers with white or yellow meat that is equally tasty. Four to six months after planting, you should be able to harvest some tubers. In ideal growing conditions, you can leave them in the ground for a while allowing the tubers to get larger.

In the right conditions of temperature and humidity, uala plants will grow quickly producing long shoots with lots of leaves and roots at many of the nodes. You can cut any of these shoots at four to six inches long and they will grow into a new plant. Though you can put the cuttings in water until you see roots growing, propagating in a tray that drains well with a 50:50 mix of vermiculite and perlite will encourage growth while preventing rotting.

Once cuttings put out new leaves, they are ready to be planted in the garden. Though they will do well in either full sun or partial shade, it is important that the soil they are in drains well. Keeping them watered until they start to spread will encourage rapid new growth. When the cuttings are well started and putting out new leaves, you can cut back on the water. Try not to overwater. You do not want to rot the tubers.

Uala plants require very little maintenance. You can prune them at any time to control growth. Light fertizing two or three times a year can keep them flourishing but is not necessary.

Rotating your crop about every two years will help keep the sweet potato weevil from finding your uala. This pest bores into the tubers and lays its eggs. When the larvae hatch, they begin eating the meat of the tuber. Root knot nematodes can also cause deformation of sweet potato tubers. Crop rotation is the best way to prevent these attacks. If these pests do appear, seek the least toxic remedy. Remember this is a food crop.

The sweet potato was often used in old Hawaii in place of taro or ulu (breadfruit). It was sometimes mashed to make poi for babies as well as adults and was traditionally cooked along with a pig in an earthen oven called an imu. It was often included in a luau feast.

It remains a popular carbohydrate side dish today. Many local markets sell the purple sweet potato calling it Hawaiian purple sweet potato or Molokai sweet potato. It is sometimes used to add color and flavor to sweet potato or haupia pies or cakes. All uala varieties are both delicious and nutritious. They are high in vitamin A, beta carotene and potassium.

Uala shoots are also tasty and nutritious. They are eaten in many cultures both raw and cooked. Salads that include sweet potato stems and leaves appear in many ethnic recipes. The shoots are also a nice addition to soups or stews.

Uala was definitely an important plant in old Hawaii. It was used for both food and medicine and was represented by the god Kamapuaa. He was described as a man with a nose like a pig’s snout making it easy for him to dig up and enjoy sweet potato tubers.

Whether you want to use uala as an attractive ground cover or an edible crop, you can usually find someone who will share cuttings. Some cuttings will be available at the Community Seed Library seed exchange on Saturday, Oct. 27 from 10 a.m. until noon on the lanai at the Kailua-Kona Public Library. Bring seeds or cuttings to exchange or just plant what you get this year and bring back cuttings or seeds next year.

Gardening Events

Wednesday: “Landscape Industry Council of Hawaii Green Industry Conference” from 7 a.m. to 6 p.m. at the Neal Blaisdell Exhibition Center at 777 Ward Avenue in Honolulu. “Education: The Key to Success” is this year’s theme. Among the topics covered in the educational sessions will be air layering and grafting as well as pests and diseases and designing with Hawaiian native plants. You can register at the door. LICH members are $150. Non-members are $205 for the entire day including lunch. A trade show will run simultaneously to the conference. For more information go to www.hawaiiscape.com/conference.

Saturday: “Work Day at Amy Greenwell Garden” from 9 a.m. to 12:30 p.m. Meet at the Garden Visitor Center across from the Manago Hotel in Captain Cook. Volunteers will be able to help with garden maintenance and are invited to bring a brown bag lunch. Water and snacks provided. Call Peter at 323-3318 for more information.

Farmer Direct Markets

Wednesday: “Ho’oulu Farmers Market” 9 a.m. to 2 p.m. at Sheraton Kona Resort &Spa at Keauhou Bay

Saturday: “Keauhou Farmers Market” 8 a.m. to noon at Keauhou Shopping Center

“Kamuela Farmer’s Market” from 7 a.m. to noon at Pukalani Stables

“Waimea Town Market” from 7:30 a.m. to noon at the Parker School in central Waimea

“Waimea Homestead Farmers Market” from 7 a.m. to noon at the Waimea Middle and Elementary School Playground

Sunday: “Pure Kona Green Market” 9 a.m. to 2 p.m. at Amy Greenwell Garden in Captain Cook

“Hamakua Harvest” 9 a.m. to 2 p.m. at Highway 19 and Mamane Street in Honokaa

Plant Advice Lines

Anytime: konamg@ctahr.hawaii.edu

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Tuesdays and Thursdays: 9 a.m. to noon at UH-CES in Kainaliu – 322-4893

Mondays and Fridays: 9 a.m. to noon at UH CES at Komohana in Hilo 981-5199 or himga@hawaii.edu