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The Honolulu Advertiser
Posted on: Friday, November 24, 2006

Grow sweet potatoes in your own backyard

By Jari Sugano

Are sweet potatoes and yams the same? Sweet potatoes are often incorrectly advertised as yams. However, they are not technically the same. Sweet potatoes (Ipomoea batatas) belong to the morning glory genus whereas the true yam originates from the genus Dioscorea.

Sweet potatoes are native to Central and South America and are an important vitamin-rich staple in many cultures. Sweet potatoes come in many colors such as yellow, white, red, purple and orange. Popular varieties in Hawai'i include the Ho'olehua gold (reddish skin with orange flesh), Waimanalo red (red skin with white flesh), Ho'olehua red (red skin with white flesh), and the Okinawan sweet potato (light skin with lavender flesh).

The majority of Hawai'i's sweet potatoes are grown on Moloka'i, yet can be grown in Hawai'i's backyards. For optimal production, plant sweet potatoes in the spring.

They prefer deep, rich, and well-drained soil with a pH of 5.0 to 6.8. Till in a well-decomposed compost material about 6 inches into the soil before planting. Hill the soil about 8 to 14 inches where transplants will be placed to increase soil drainage and provide tubers with adequate room to develop.

Plant transplants about 4 to 5 inches deep, with buds above the ground. Space plants about 10 to 12 inches apart, with 3- to 4-feet rows.

Sweet potatoes are started from vine cuttings or slips. Starter material can be purchased from your local garden shop, or you can sow your own planting material. The easiest way to get started is to purchase a sweet potato with your desired characteristics (skin color, flesh color, flavor, etc.) from the grocery store. Avoid sweet potatoes with excessive pest or disease damage. Keep the sweet potato in a moist area or plant it a few inches below the soil surface to serve as a seed crop. As new sprouts emerge, cuttings of 12 inches can be used as planting material.

A fertilizer such as 10-20-20 or 16-16-16 can be applied at planting to encourage vegetative (leafy) growth. As tubers begin to set, minimize nitrogen applications and increase potassium applications to encourage tuber development. Overapplying nitrogen will result in excessive vegetative growth and minimal tuber development.

Be consistent with your irrigation, since excessive watering can cause tubers to rot and insufficient watering can cause tubers to crack.

Five to six weeks after transplanting, soil should be re-fertilized and hilled around the plant to increase crop quality and minimize weevil damage. The sweet potato weevil is the predominant pest for backyard operations. Maintaining good sanitation and cultural practices can aid in minimizing weevil problems.

Sweet potatoes are usually harvested 120 to 180 days after transplanting. They should be harvested with care, since skins are thin and delicate. Sweet potatoes aren't consumed immediately after harvest. Potatoes should be cured in a warm and humid area for five to 10 days. After curing, potatoes should be kept in a cool and dry area.