Prepare a sunny site for planting by tilling it and working a potassium source such as wood ashes into the soil. Add compost and sand to the soil to increase its drainage and nutrient qualities. Install a trellis or climbing strings for the plant.
Soak jicama seeds in warm water overnight before planting and drain them the next morning. Only soak them right before you plan to plant, when the soil is warm and all chance of frost is gone.
Plant the seeds six inches apart by pressing them about one inch into the soil. Position the rows 12 inches apart.
Water the jicama moderately, about one inch per week.
Mulch around the plants with an organic mulch such as compost or manure after they are established -- with at least three leaves around the base. This adds nutrients to the soil and keeps weeds at bay.
Remove flowers from plants after they appear. This encourages the roots to grow larger.
Harvest the jicama in the fall using a pitchfork as you would for potatoes.
Jicama requires five to nine months to become mature. The longer they are in the ground, the larger the roots will be.