We get regular reseeding here in zone 5b/6. It does not like our heat in mid-summer, either.
Depending upon location, reseeding can be almost invasive. Up where I manage some demonstration herb beds, each spring we have to yank lots of it out. I love the purple flowers, and the fact it is edible and an attractor of pollinators. I plant it near my tomatoes, so the borage gets some shade from the larger tomato plants. It seems to reseed more gently in partial shade.
