The Murasaki sweet potato, originating from Japan, is popular for its deep purple-red skin and pale cream-colored flesh. This root vegetable offers a distinct, nutty, and chestnut-like flavor profile, which is less intensely sweet than common orange varieties. Botanically classified as Ipomoea batatas, the sweet potato is not a true tuber like a potato or related to yams. Murasaki sweet potatoes require a long, warm growing season, needing a minimum of 90 to 120 frost-free days to fully mature.
Preparing and Propagating Slips
Growing Murasaki sweet potatoes begins with a rooted vine cutting known as a slip, which is sprouted from a mature sweet potato. Initiate this process indoors about four to six weeks before the last expected spring frost. To encourage sprouting, suspend the potato in a jar of water using toothpicks so the lower half is submerged, or embed it horizontally in damp sand or potting mix. Placing the potato in a warm environment, such as on a heat mat or near a sunny window, will accelerate sprout production.
Once the sprouts emerge and reach approximately six inches, carefully twist or slice them off the parent potato. These slips can then be placed in a glass of water to develop root systems, which usually takes about one week. Pre-rooting the slips before planting gives them a stronger start and helps them establish more quickly in the soil.
Establishing Optimal Growing Conditions
Murasaki sweet potatoes thrive in warm conditions, requiring warm soil for successful establishment. Delay planting until all danger of frost has passed and the soil temperature consistently remains above 60°F (15°C), typically in late spring or early summer. Using black plastic mulch prior to planting can help increase the soil temperature.
Sweet potatoes require loose, well-draining soil; sandy loam is ideal for root expansion. Avoid heavy clay soil, which impedes the development of large storage roots, unless amended with generous amounts of organic matter or by planting in raised beds or 8-inch high hills. Set the slips into the mounds at a depth of 2 to 3 inches, ensuring two or more leaf nodes are buried. Space plants 10 to 14 inches apart, with at least three feet between rows to allow the sprawling vines ample room.
Ongoing Care and Vine Management
After planting, consistent moisture is necessary during the first week to help young plants establish their root system. Once established, sweet potatoes are drought-tolerant, but they produce a larger yield with about one inch of water per week. Avoid over-fertilizing, especially with high-nitrogen formulas, as this encourages excessive vine growth at the expense of root development.
Vine management, often called “pinning” or “vine lifting,” is a common practice. The vines tend to root at the leaf nodes where they touch the soil, creating small, non-productive potatoes. To prevent this energy diversion from the main storage roots, periodically lift or gently move the vines so they do not anchor themselves. Monitor for pests such as sweet potato weevils, though Murasaki sweet potatoes are resistant to issues like fusarium root rot.
Harvesting and Post-Harvest Curing
The Murasaki variety requires a long maturation period, with harvest occurring between 120 and 140 days after planting. Yellowing foliage is a visual cue that the potatoes are nearing readiness, signaling that the plant’s production is slowing. Harvest must occur before the first hard frost, as temperatures below 55°F can damage the tubers and affect storage quality.
To harvest, cut away the vines first to clear the area and prevent disease transfer to the roots. Carefully dig up the potatoes using a garden fork placed 12 to 18 inches away from the main stem to avoid bruising the thin skin. After harvesting, curing begins; this process converts starches into sugars and heals minor skin damage for long-term storage. Curing involves holding the sweet potatoes at high temperature and humidity (ideally 85°F at 85-90% humidity) for 7 to 10 days. Properly cured Murasaki sweet potatoes have superior flavor and texture compared to those cooked immediately.