How to Grow Japanese Purple Sweet Potatoes

Start plants by cutting the growing end of existing vines or cut out sprouted areas of purple sweet potatoes. If you use cuttings, include at least three or four nodes. Begin your sweet potatoes in March if you live in a frost-free zone, or as late as May in other regions.

Enrich the soil in your planting area by combining one part organic compost with every four parts of soil. If your soil is relatively free of rocks and contains some sand, this will give it good drainage, which this potato needs.

Create raised beds or ridges that are 8 to 14 inches tall. Make your raised rows 4 feet apart. To do this, scoop up soil from either side of the row and pile it on top. Turn it under well with your shovel.

Plant cuttings 4 to 9 inches deep and 10 to 12 inches apart, making sure you include three to four leaf nodes. If you're planting sprouted potato chunks, plant them at the same depth and distance apart.

Create hills on top of your rows five weeks after you plant your cuttings or sprouted chunks. Dig up more soil from the area next to each row and pile it on top of the growing area about 3 inches deep.

Keep your sweet potatoes well watered; in Hawaii, for instance, they thrive in areas that receive 120 inches of rain a year, so keep the soil moist. Stop watering your Japanese purple sweet potatoes about one month before you harvest them.

Fertilize your sweet potatoes only if your soil is lacking in nutrients. Use a balanced plant food such as seaweed extract and apply it when you first plant, six weeks later and again in 12 weeks. Using compost that contains wood ash is beneficial.