I'm growing several European hybrid strains of Penstemon (Twizzle and Rondo) that I started from seed and now have growing nicely inside under growlights. I also winter-sowed several species in milk jugs which surprisingly are doing reasonably well (though still only tiny seedlings) considering they're growing in regular moisture-retentive potting soil: P. pallidus, P. grandiflorus, P. richardsonii, P. serrulatus, P. tubaeflorus, P. cardwellii, P. cardinalis.
I also purchased several plants of European-bred Penstemon hybrids (Arabesque, Red Riding Hood, Mesa). I also have on order plants of the straight species Penstemon ovatus and P. smallii.
So I have a lot of Penstemon in progress, with a diverse mixture of types. I figure I'll be ready to plant some of these in a week or two; others, not until next month.
However, I just don't have the ability to create any sort of rock garden right now and need as best as I can to rely on my moist, organically-rich New England soil. My question: if I did want to give these seedlings some of the fast drainage they want - especially the midwesterners - would it better to dig gravel (or sand?) deep into my soil, or should I spread a layer of gravel as mulch on the surface? Thanks for any thoughts.