When to start seedlings?

Garden Wizard and Garden Master CD's have

When to start seedlings is an important question - no matter where you live,
and the answer is always the same - "When they won't freeze!" So when is
that? It depends on the plant and your weather. First find out the average
last frost date in your local growing micro-climate. The Garden Wizard and
Garden Master CD's do a good job of giving you that for over 3,000 places
in the United States. Others will have to ask your local government Ag.
Extension agent.

Next, determine the frost tolerance of the plant you're growing, to know
when to transplant into the garden. There are 4 levels of frost tolerance -
and I quote from the Mittleider Gardening Course:
1. Hardy plants tolerate frost and cold and can be planted 3 to 6 weeks
before the average date of last frost.
2. Moderately-hardy plants handle a certain amount of cold. Plant these
2-3 weeks before the average date of last frost.
3. Cold- and frost-sensitive plants don't like cold or frost. Plant them
on the average day of last frost and protect them against late
frost.
4. Frost-intolerant plants will not survive any frost and must be
planted 2-3 weeks after the average day of last frost.

With dozens of plant possibilities, I can't tell you here what each plant's
frost tolerance is, but again the Garden Wizard and the Garden Master CD's
give you all of that.

And finally, you need to know how long your plant needs to be in the
greenhouse before being transplanted, in order to get back to the date on
which you plant in the greenhouse. And again I refer you to the Garden
Wizard and Garden Master CD's as the best place to find that information.
Remove the uncertainty and confusion in this very important step by looking
in the Preview Plants section of the Garden Designer. You will learn the
number of days required from planting seeds to transplanting in the garden,
for all the common garden vegetables.