Maybe the 'maters kept the soil cool enough for it to approach the optimum temperature for 'tater tuber growth.
We grow really good 'tater crops here in zone 2 because our summers are relatively cool, with long days.

This post was edited by Slimy_Okra on Tue, Sep 3, 13 at 19:20

Typically I plant radicchio under the toms, and get decent size heads, but much of the growth is in Fall.

I've always read to keep tomato and potato plants apart because they are in the same family and share the same diseases.

Sometimes I've found tomato volunteers in the potatoes. And everywhere else.