My first attempt at growing tomatillos from seed resulted in only one plant. I planted the one, and it did spectacularly well: tall with flowers galore. It overtook its allotted spot, spreading into the neighbor's side. But, strangely, there was no fruit. I checked the seed package; it made no mention of needing two plants to get fruit.
I turned to the Google, and, whoa, it turns out tomatillos need another tomatillo plant near by in order to produce fruit because they don't self-pollinate in the same way as tomatoes. This left me somewhat annoyed because I really wish this little piece of information had been on the seed package instructions and because it is getting late in the season. I hurriedly bought and planted another seedling. Several weeks later, while I don't have an abundance of fruit, it looks as though some cross-fertilization happened. I have some baby tomatillos on its way. Relief. Moral of this story: it takes two [tomatillos] to tango.