Let's put this bluntly; some seeds are just a bitch to germinate. Once when using morning glories for an experiment, to get good germination all at once, the seeds were washed in concentrated sulfuric acid for a few minutes and then washed in water. A good deal of the seed coat was dissolved, but the embryos within were undamaged and the seeds all germinated at once. A lot of our temperate zone seeds need a cold period, often several cold periods, alternating with warmer periods to convince them that spring has sprung and they should germinate. This is called vernalization. Some seeds need considerable washing to remove germination inhibitors, a mechanism to assure germination just after sufficient rainfall. Some prairie seeds actually germinate better after a fire. In an effort to mimic a fire treatment in a safe and controlled manner, a student researcher took some difficult to germinate seeds (a legume), packaged them in little filter paper packets, constructed a lab-style double boiler, and steamed the packets for 4 mins. They germinated like crazy after only a 1 week cold period! Seeds collected from litter after an actual prairie fire also germinated OK, but not quite as well probably because some were cooked and some were not heated enough. The untreated seed, no fire, no steam, just sat there week after week. The after-a-fire germination is a good strategy too because after a fire because the accumulated dead plant material is removed so seedlings will get more sun and the ash is full of nutrients. Now to try the steam heat method on a couple of other very stubborn seeds.