While Verbena bonareinsis is a South American flower, it still needs cold stratification to germinate.
I can’t count on just throwing down seed in the fall or just planting seed in the spring, so I’ve done some testing with cold stratification.
I’ve tested a number of refrigerator and freezer methods and the one which has done the best is….
Seed plus moistened vermiculite in a large plastic bag.
I kept it in the refrigerator for 5 weeks.
I prefer using vermiculite since it mixes with the seed and comes out of the bag easily.
I then cover the seed with a bit more vermiculite.
After about ten days, below is what came up.
Butterfly Gardening 