in short, yes and no. yes as a one-time thing, you can plant them close. next year and beyond would be a no-no, for these reasons: they're in the same family, along with potatoes and eggplants. so they're using the same nutrients. this means that the soil will get depleted for their family members, and you'd have to fertilize more and more heavily. and they have the same basic chemical outputs. they are loved by the same bugs and diseases, so once one gets infected, it can jump to the next very easy. you'll have to watch them carefully for bug condos, as any touching plants can transport insects and diseases easier than if they have other types of plants in between. google up "companion planting" to get some better neighbors for the 2 of them. here's one link to start: http://organicgardening.about.com/od/vegetablesherbs/p/tomatocompanion.htm