According to experts at the University of Wisconsin, if you plant the seeds now, and rosettes grow well this summer, you will be rewarded with flowers each year thereafter so long as the cycle continues.  

Although foxgloves self-seed readily, seedlings may fail if they are disturbed or do not thrive because of drought, shade or other unfavorable growing conditions. Some care and attention to their welfare is warranted. 

https://hort.extension.wisc.edu/articles/common-foxglove-digitalis-purpurea/

You can also start seeds indoors in late winter or early spring.  Dalmatian foxgloves are said to bloom in fewer than four months from seed and may bloom the second year if flower spikes are removed.