Here is some general info for USDA zone 5a to help you get started.
|Average Date of Last Frost (spring)
|Average Date of First Frost (fall)
|Lowest Expected Low
|Highest Expected Low
This means that on a really cold year, the coldest it will get is -20°F. On most years you should be prepared to experience lows near -15°F.
Below is a list of planting guides for Zone 5a.