Our average frost fee date for our area can be as early as about May 5th, but could be as late as May 20th. Move north from here and it is going to be later, head south and it will be sooner. Depending on the micro climate in your own yard the date can move as well. The average frost free date is the date where there is actually a 50% chance that we could still get a frost or light freeze. Gardeners can do their best planning and still end up in a bit of a gamble.
There are vegetables from seed or transplant that welcome cold weather and frosty conditions. Others prefer or even need warm air and soil temperatures. This range of growing conditions starts 4-6 weeks before the average frost free date and goes beyond that date by 2-3 weeks, so you can see lots of planning is in order to make those planting dates.
Typically gardeners rank or talk about these different seeds and transplants in terms of their ability to grow from seed or survive and thrive as a transplant over this wide air and soil temperature range. "Very hardy" vegetables start the list and can be sown or transplanted 4-6 weeks ahead of that average frost free date. The next groups down the list are those considered "frost tolerant" being sown or planted about 2-3 weeks ahead of the average frost free date. You still have to go out and cover them if a light freeze is expected, but they do not mind a little frost. Those "tender vegetables" get to be sown or set out on the magic date and absolutely will need to be protected from even a light frost. The last group really needs warm air and soil temperatures to get off to a good start and we call them "Warm Loving" and can be sown or set out 2-3 weeks after that average frost free date.
After the spring plantings are all in, the next plantings will be the successive plantings that carry into the summer. By midsummer gardeners thinking about the fall garden are already planting transplants and seeds again of those cold weather tolerant vegetables. To get a full season of gardening in, it takes a lot of scheduling, time and dedication to growing your own wholesome vegetables.
To sum this column up, if transplants are going in as early as mid to late April and the seeds take 4-6 or 8 weeks to get to transplant size and quality, then you only have about month to get ready before it is time to sow!