Yes - there are tons of variables. This past winter, I planted 6 each of the same milkweed species, Common, from six vendors - knowing it was unlikely they would all germinate. I was certainly correct. Not one single seed germinated from 3 vendors. One vendor, all 6 germinated, the other two ~ 2/3rds germinated.
Since they were all planted on the same day in the same medium in the same tray, they were all exposed at my end to the very same conditions.
