In zone 4, we'll be starting seed of tomatoes and peppers inside, of course. The earlier you start, the large the transplants you will have. I start my tomatoes inside April first. Peppers about March 10. Peppers need warm temps to germinate well, at least 70F, without going down at night. 80F is much better. For me, plants don't need to be big, they just need to be healthy.
For cool weather crops like lettuce and radishes (apparently, I'm in the minority of people who like radishes
), whenever the soil is workable is fine. Planting in soil on top of frozen soil, as Chelle describes, is fine too. If it is too cold, the seeds will just wait until the time is right to come up.
