Some of you may have seen grafted tomatoes cropping up in garden centers over the past couple of seasons. But what really is the difference between a grafted tomatoes and non-grafted tomatoes? Grafted tomatoes have turned up for many of the same reasons that we graft other plants. Tomato grafting first because practice in the 1960s when grafting was mainly done to make the tomato plants more disease resistant. Now, grafting is done for a number of different reasons. Sometimes growers graft tomatoes so that they are more resistant to abiotic stresses (salinity, drought, flooding) or they choose rootstocks that are better suited to their growing conditions (soil, temperatures, etc). This hardier rootstock is then attached to a scion (aka "the top part") of a variety that the growers want. In some cases, grafting can also cause the tomato plant to be higher yielding, extending it's growing season at the beginning and the end.
One common factor among grafted tomatoes that you'll see when you're shopping around your garden center this spring is that, usually, these plants are more expensive than your normal tomato plants. For some, the cost is worth it for the higher yield and higher tolerance to several factors. But if you want to try your hand at grafting and skipping the higher prices at the register, here's a step-by-step tutorial for grafting your own tomato plants.