Here's the problem. Oca's summer flopping wouldn't be so bad if it was producing tubers during this time but it doesn't. Like a lot of tropical plants Oca is a short day plant, meaning that it won't start producing tubers until the amount of day light is around 12 hours (or less) which for Melbourne, after summer, occurs at the autumn equinox on or around March 21. Having grown Oca for three years now it is extraordinary how tuber formation begins at this time like clockwork. The stems begin to produce stolons or subsidiary stems and then swell into tubers. Now as autumn nights get colder and longer this tuber production will continue until late May and even into June as long as you are in a frost free area.
Have a look at the pictures, I hope it's relatively self-explanatory. I'll blog again about how they're going in about a month when I expect they will be ready to harvest or at least "bandicoot". By the way, Tansy the chef who runs the cafe at Burnley (whose partner John is an Oca-loving Kiwi) let me know that the potato man (Michael J Mow Gourmet Potatoes) at the Prahran market sells Australian grown Oca every year. This should be very soon I hope (see http://theindolentcook.blogspot.com.au/2010/09/oka-yams-love-at-first-bite.html. for an account of someone getting into Oca for the first time).