I hope someone chimes in, but 6b to 7 doesn’t sound like a huge jump. I would try it! :)

Never mind supposed zonal suitability, note the above says "Root hardy to 10-15F" - that is the key statement. One which means even the roots die if it gets below 10-15F.

I have grown this several times and have never gotten it through the whole summer alive - it seems this plant just does not like the heat and will melt and die no matter what you do for it.

Set the young plants out early in the season as possible, they will produce flowers but if your summer temps go into the 90s they just don't live through the heat.

I have grown this both from seed and purchased plant as an annual, that bloomed beautifully for me all summer in Minnesota. I have been looking for seeds for several years and located both the light purple and white this year. Have moved to zone 7 so also keeping my fingers crossed on survival.