Natural yards are designed to suit their location. This post begins a series on site conditions that are important to consider when planning a natural yard.
Hardiness zones correspond to the lowest temperature a given area is likely to experience in an average winter. Lower zone numbers correspond to colder regions.
Seeds and plants are typically marked with the range of hardiness zones where that species is likely to survive. For example, a plant marked 6-9 would be happy anywhere in Texas, but would not be a good choice for Wisconsin.
Madison is located in zone 5. Choosing plants native to this region is a sure bet, but using non-natives marked for this hardiness zone is also likely to be a successful strategy.