For me, it can vary so much year to year. Sometimes it's trending really warm and we're seeing days in the 60s in late March and nights staying mostly above freezing. If that's the case, I might start some annuals then. Last year the weather was cold, dreary, and rainy and we rarely saw sun. I think it was well into April before I did annuals.
If I have tender sprouts and we get a frost, I flip the tops shut and cover with a sheet or blanket. Sometimes I put them on my porch for a little extra protection, or even in the unheated garage overnight. Then they go back outside in the morning.
The way our weather has been so far this year, I'm not expecting a warm spring.
Karen