I guess the rule of thumb is Mother's Day for planting annuals around here. Just for an experiment, I direct sowed some marigolds last fall. Sure enough, they are sprouting. The seeds actually survived the winter. Cosmos seeds also survive the winters.

In Nevada at about the same altitude and latitude as SLC I am doing some serious direct sowing this week.

(I always start with a half dozen seed two to four weeks earlier. I have three sunflowers from a month ago that have survived several mornings of 30°F and one snow. Perhaps our only snow this year was about May 5th.)

With the weather forecast along the Wasatch Front in the 80s/50s for the next 10 days, I'd say we're now safe for planting. I'll be planting some zinnias, marigolds, corn, and a few other things this week (if our cute new baby gives me enough time, that is!).