Burpee apparently isn't telling us what root stock they used. Other companies also are doing grafting, but I haven't gone to their sites to see if rootstock varieties are listed. Territorial Seed is one, Johnny's Selected Seeds is another. I found quite a bit of interesting information about grafting tomatoes for those who would like to try growing and grafting your own. The following link will give you access to many pages of how-to information.
http://www.ask.com/web?am=broa...
Caroline, I always plant tomatoes horizontally, in a little trench with a slight incline so that the root end is about 3 inches under what will be the soil level after it's covered with soil, and the top gradually comes out the shallow end. I place them so that about 1/3 of the top of the plant is all that is visible. In a couple of days that top will turn itself upright, and all that buried stem will sprout roots. A deeper hole for planting upright would put the roots down into cooler soil where they would not be as happy. I stick the pot label near the root ball and have them all going the same way in the row. If staking or caging them, then I know where it is safe to put a stick in the ground as long as I do it within about a week, before that root ball gets much larger. I'll have to search out my picture of one of the plants when I pulled it out in the fall.
