That's a hard one. Shirley should have slightly smaller flowers and be a shorter plant than Sarah but they could look similar blooming. I didn't think Shirley had the red edging and it's supposed to bloom earlier than Sarah by a couple of weeks; if anyone knows for sure about the possibility of red that might be how to tell which yours is. In my experience Sarah only has an issue with holding up the blooms after they've gotten wet; at least before the plant is fully established. I think both have sidebuds once the plants are bigger and that's when Sarah runs into more issues with holding blooms up even without rain or wind.
