Planting the tubers
Getting started -- For soil, use a rich, but well draining soil. A typical mix is 2 parts potting soil to 1 part perlite or coarse horticultural sand.
Fill 1-gallon pots (4 liters) to within 3 inches (8 cm) of the top with the soil mix, place a tuber on it, and cover with an inch (2.5 cm) of soil.
Add water until lightly moist throughout, but not soggy. Until the tubers sprout, keep at room temperature (65-72°F / 18-23°C) or slightly cooler, with some air circulation. Until shoots appear, keep the soil lightly moist.
When the shoots break through the soil, place them in bright light, with shade from strong afternoon sun. You may increase the watering a bit once growth begins.
After 3 months of growth, repot to a 3 to 5 gallon (11-19 liters) container, or into the ground, in frost-free areas. You will be "mounding up" soil over the plants later, so leave 4 inch (10 cm) of free space below the top of the pot.
Keep the soil evenly moist most of the time, and never let it dry out completely. Feed about every 2 months with a slow-release (pelleted or organic) fertilizer. In warmer climates, provide some afternoon shade, and keep the pot shaded so the roots stay cool.
Like potatoes, the edible tubers form on underground stolons. In the summer, start mounding dirt up around the base of the stems to encourage stolon formation.
They begin developing tubers in late summer as the day length shorten to 12 hours per day. The tubers normally take another few months to mature and are usually ready in late winter. They should be protected from frost until they are harvested. The foliage above ground usually dies back when the roots are ready, but this doesn't always happen. They may continue to grow a bit after the foliage dies back, so try to leave them in the ground an extra week or 2 after the foliage dies, assuming there is no hard frost predicted.
You may wish to leave the roots in the sun for a few days. This does two things: it increases the sugar content, plus it reduces the oxalic acid naturally found in Oca. Oxalic acid may cause problems for some people who are prone to kidney stones. Cooking or par-boiling the tubers also reduces the oxalic acid content.
Eating Oca -- You may eat Oca fresh, or use them in a variety of recipes in place of potatoes or spices. Check Google for "Oca recipes". The skin is edible - just give it a good brushing under running water.
You can store your Ocas in the door of a refrigerator for many weeks, or sometimes months. Just check on them periodically, and if they show signs of deterioration, plant them right away.
Have fun growing them!
Strange Wonderful Things