Stevia Flowers

My potted stevia plants are making the prettiest little green flower bunches. They are still looking pretty good despite all the hard frosts we've had. I'm not sure if that's normal for this plant or if it's because they're planted in pots and the pots are somehow protecting them. It's neat, though. I hope they make seed - stevia seed is relatively pricey, so I'd like to see if it can be saved.