They said it was extremely difficult to cultivate, but they were able to get them to sprout using cold stratification... Kind of a basic technique nowadays. Lavender, hardy hibiscus, some geraniums, phlox, Chinese lantern, black-eyed susan - all of these common plants need cold stratification to germinate. Home gardeners utilize a plastic bag and their refrigerator. I'm sure this was more vexing in ancient Rome, but the article was talking about cultivating the modern plant in question. Unless there was a lot more to it that the article glossed over, "extremely difficult" is not the the term I'd use to describe the process. It's one of the basic techniques propogators try with a new species when dropping the seeds in the dirt doesn't work.