Strawberry foxglove (Digitalis x mertonensis) is said to be a perennial, so it should keep returning year after year, regardless of whether you cut off flower stalks before or after blooming, or at all. (I haven't found it to be hardy in my yard, so don't have personal experience with it.)
Lots of people who had this plant (and other perennial ) Foxgloves , say they did not return if left to seed , if the stalks were continually cut after bloom, they say there is a stronger plant as to flowers and eventual return of another season ,
That is and was what I wondering about . When you say no hardiness for you ? I have heard that (or read) that from many from my zone to yours .
The question is because the plant we were(or are) talking about (Foxglove) is suppose to be . (I am aware you know that already) I have heard you prefer the Pentstemon forms of Digitalis ..When you were talking on other threads .
Some examples of perennial foxgloves are Digitalis grandiflora, Digitalis lutea, Digitalis lanata, etc. - they are long-lived (here, at least) regardless of whether the flowering stems are cut off before or after blooming or at all. If you're having problems with foxgloves coming back, you might consider avoiding biennial species and ones that are described as "short-lived perennials", and try the ones listed above? (Unfortunately, they are not near as showy as the more desirable but biennial or short-lived ones.)
I don't know what you mean by "Pentstemon forms of Digitalis" (Penstemon and Digitalis are different genera). However, there is a species of Penstemon called Penstemon digitalis (e.g. Penstemon digitalis 'Husker Red') - I wonder if that's what you're thinking of? (A nice plant but if I could only pick one Penstemon to grow out of the 270 or so species, it wouldn't be that one!)
Anyway, good luck with the foxgloves.
Probably thinking about Bearded Penstemon Digitalis something or another , Little lol here memory is not what it could be ,
The only Penstemon I have is Dark Towers and I do not believe it is hardy where you are either , Beautiful plant though .