Inspired by a question at the Facebook group. In addition to yacon, I grow four of its wild relatives: Smallanthus connatus, S. fruticosus, S. maculatus, and S. uvedalius. These all have similar characteristics that are important to germination. They have heavy seed coats and benefit from scarification. For small amounts, rubbing on sandpaper is good enough. If you make a hole, you went too far, but the seed will probably still germinate as long as you didn’t damage the contents. If you have a lot of seed and don’t care about waste, you can skip the scarification. Some of the seeds will eventually germinate even without it - you will just have a lower germ rate and it will take longer. Soak the seeds in water after scarifying, eliminating any that do not eventually sink, as they are probably empty. Then plant about 1/4 inch deep. I do not recommend direct planting because these seeds can take so long to germinate that you might lose them, but if you want to direct sow, do it only after your daytime soil temperature is certain to be 80 degrees F or more. Keep the soil moist and warm. I use a heat pad set to 90F during the day and 70F at night. I have had seeds germinate in as little as 10 days under these conditions, but more commonly a month or more (sometimes much more).
An alternative for direct sowing, particularly if you have a lot of seed, is to plant a little more deeply, water in well, and then burn brush over the top. These are species of woodland edges and probably are naturally fire succession plants. I wouldn’t recommend this for the species with scarce seed, but S. connatus and S. uvedalius both produce a lot of seed and would be worth an experiment.