Plan for an indoor planting date 6?8 weeks before the tubers are to be transplanted outside, after the last frost date. Place tubers just below the surface in a flat of moist soilless potting mix. The indented, or concave, part of the tuber-where the buds, or eyes, may be present should face up. Tubers sprout best at temperatures at least as warm as 60 F. Keep the soil moist but not soaked. When newly sprouted leaves reach about 3 inches, shift the tubers to larger pots and continue to grow in bright light.