In order of importance:
- Don't grow Oca in an area prone to early frost. Tubers only start to form after the equinox (about 22nd Sept), so if you commonly experience frost in September or October, the crop will be light or non-existent unless you provide crop protection. Most sources describe November or December as the normal harvest time, but for a big harvest, try to keep the plants frost-free until mid December.
- Wait! After the killing frost, wait for 14 days (according to most sources), or possibly 21+ days (somewhat supported by my results), before harvesting. This gives time for the plant biology to finish turning plant tissue (some of which is hidden below ground) into tubers. Waiting a few extra days can have a noticeable effect on tuber yield (subject to Tip 3).
- If hard weather is forecast between the killing frost, and the prescribed harvest date, consider lifting early, earthing-up, or adding physical protection/insulation. If you don't do this, you may loose some of the crop to penetrating frost (which makes tubers unusable), or foraging rodents. This is especially important if tubers are showing at the soil surface — crowded swelling tubers can push themselves up during the final weeks.
- Water thoroughly during dry periods in late Summer and Autumn. The plants develop a lot of foliage during this period and moist conditions help to support it. Mulching in early Summer conserves moisture, and this same mulch will help to insulate the tubers from frost later in the year.
- Give them root space, sprawl space, and light - especially in late Summer.