You probably have an extension agent right in Durham county that you can ask. I am south of you and generally our last frost date is April 15th. It is tempting to plant as soon after that date as possible, but tomatoes like warm soil and will just sit there until the ground is warm enough to really start growing. If the ten day forecast indicates that you won't have anything below 40 degrees at night after the 13th, waiting the week or two after that should be fine (plant about the 25th). Believe me, the risk of loosing your plants to a sudden cold snap far outweighs getting the plants in the ground too early. Also, because Lowes has tomato plants for sale does not mean you can plant them outside. I've seen frost kill their stock all the time!! Are you starting seeds?

I remember a frost the first week of May a couple of years ago. I can only sow so many seeds inside since my shelf space is limited so I save tomatoes and basil for last which usually ends up being mid April or later. Both of them are soooo picky about temperature that it just isn't worth it starting them early. There are plenty of other things to work on that enjoy the early cool temps.

Trianglejohn:
I remember that frost also! I have started onion plants in the house this year for the first time. Have you ever done onions from seed? I used to do sets but last year I bought plants and had the best onions ever. This year I am raising my own onion plants.

I always grow mine from sets and I usually don't grow them at all because I don't eat that many and they are so cheap in the store. I would like to try some of the specialty ones though. I have always heard that home grown can taste much better. My sunshine is limited so I tend to grow a big crop of something one year and freeze it and then grow something different the following year. This year I have onions (white) in the ground, grown from sets.

There was a post on GardenWeb, over in the farm forum or veggie growing forum, years ago from someone that knew a lot about growing onions. They claimed that starting them from seed was not the easy way, but that it gave a much better bulb in the end. It was something about onions being biennials and that exposing the actively growing plants to winter chills will cause them to switch to their second year "I'm gonna bloom" schedule. Whereas if you sow seed early inside and then set them out in early spring they only make extra large bulbs by fall. It was her way to have nice uniform large onions to sell at the farmers market. Someday, when I get a bigger garden space with better exposure I will be sowing a lot of onion seeds.

The way the weather has been the last few years I would not use last average frost date as a guide to do anything. Tomatoes are heat loving plants and if planted in soil that is too cold, will just sit there until the soil warms up. Consider growing tomatoes in containers since the soil in them will warm up much faster and give you ripe tomatoes much earlier.

Thomis, I believe I would listen to the posters above re specific dates BUT with regard to your specific question that related to average and standard deviation and the 13th (avarage last frost) and 1 standard dev SD being 12 days; this means that there is approximately a 67% chance the last frost will be between the 2nd and 25th of April and a 97.5% chance it will not be after the 7th of May (+2sd). The recomendation of 1 or 2 weeks after the average was a compromise of less than one sd away from the average which would seem risky even from a mathamatical standpoint because it suggests at least a one forth chance of a freeze after planting. On the other hand, perhaps tomatoes can stand a light freeze and a heavy one is less likely.

Entire books have been devoted to gardeners trying to be the first person on the block with a ripe tomato. It isn't worth it. The chemicals in a tomato that give it its distinctive "homegrown" flavor are destroyed by temperatures below 50 degrees - this is why you shouldn't store tomatoes in the refrigerator. So even if you rush the season and get your plants to fruit early they aren't going to taste any better than the "chilled-in-shipping" one's you can buy at the grocery store. Sow them in May when the temps are reliably warm and you'll have great tasting tomatoes sometime in June.

Great information from all!

Plant 'em the first or second week in May and you'll be fine. (Of course if your 7 day forcast looks good you can push this into the end of April....)
You can use cold frames/black plastic to warm up the soil
and get them in a week or two earlier, but usually it's not
worth the effort.

Your best bet if you want something earlier is to plant a couple of ealry ripening varieties. I had Sungolds last year
in 51 days from transplant.... Mid/End of June tomatoes!

Lee

P.S. A good rule of thumb for maters in central NC is
seed start Feb end
transplant Mar end
plant out Apr end

Books may have been written on anything, but the simple fact is that tomatoes will not produce much growth when the soil is cold. Planting in containers where the soil temps. will warm sooner will give you tomatoes sooner since by then the air temps. will have warmed enought to give you good tasting tomatoes. Soil temps lag air temps by leaps and bounds. Give it a try if you haven't tried it!

Good info for me guys!! I just started seeds today, Beefsteak and Roma's. My plan is to grow a few in containers and more in both a regular garden and a raised bed. According to my calculations, they should be ready for the ground around the end of April and I'm just a touch warmer than you guys are.