My vinca does fine in shade

Are you talking about Catharanthus roseus aka Vinca aka Madagascar periwinkle or as in the creeping groundcover Vinca minor aka Periwinkle aka Myrtle?
This is the problem with using common names for plants instead of botanical names.
Vinca minor or Vinca major, the creeping groundcover that is evergreen and has blue flowers in spring will do well in part shade.
Catharanthus roseus, and annual flowering plant that somewhat resembles Impatiens prefers full sun. Here's a link to info about the latter.

Here is a link that might be useful: link

My vinca does fine in part shade, and since we are on the annuals board, I will assume you are talking about the annual vinca and not the Madgascar periwinkle which is a perennial vine/groundcover thing.

Catharanthus roseus (annual Vinca) is a full-sun plant in this zone. It *may* get by in five or six hours of sun, but that's pushing luck - it will tend to get a bit leggy and just not flower well. Also, do not overwater it, very sensitive to overwatering.

My favorite annual Vinca is Blue Pearls, just love the lavender color, and I also like the pure white with the tiny red eye. :)

I'm in Z6b in south-easter part of PA. We have had a cool dry spring and many things are late.I planted the thing sold as an "annual vinc-vine" in one of my deck planters last year. It grew out of the pot, over the deck,down to the ground, and under the deck. This spring I discovered that it had taken root under the deck. It is in full-shade. Not only did it over-winter, but it is spreading like crazy underneath of my whole deck and creeping into my garden. It looks cool for now, however, I am now starting to worry that it will eat my garden. So if yours is the same as mine, it does well in shade, even full shade.
Good louck.
JD