On this post, you'll find listed a number of vegetables and the dates by which they should be planted in the ground. The information provided here is based upon graphics and documentation provided from this Virginia Cooperative Extension 2009 PDF document, publication #426-331 via the Virginia Tech website.
Though the planting dates are specifically calculated for growing in Hardiness Zone 7 in Virginia (based upon average date of last frost), this information may also be used fairly accurately for Zones 7 in the adjoining states North Carolina and Virginia (Mid-Atlantic region of the U.S.A.).
Based upon information in the PDF document, the average last date of frost for my specific area (Fredericksburg, VA.) appears to be around April 25. Therefore these calculations are based upon that specific date.
NOTE: The last frost for your area may be slightly different. To accurately adjust for your specific location, you will need to research & determine your average last frost date. For example, if it's April 15th, deduct 10 days from the given planting time frame, and if it's May 5th, add 10 days. If you're not quite sure, just use the dates given below.
Planting dates for Hardiness Zone 7 (Virginia & Mid-Atlantic, USA), starting from June 29, 2011:
If you live outside of the region specific to this article, the good news is that many of these same vegetables may still be grown for the 2nd half of the growing season. You will need to do your own research to identify your specific planting dates.
DISCLAIMER:Dates are not exact, only an estimation based on previous year's averages. Yearly results may vary due to climatological conditions (rainfall, heat), specific soil conditions, and individual care.