Here is some general info for USDA zone 6a to help you get started.
|Average Date of Last Frost (spring)||April 15|
|Average Date of First Frost (fall)||October 15|
|Lowest Expected Low||-10°F|
|Highest Expected Low||-5°F|
This means that on a really cold year, the coldest it will get is -10°F. On most years you should be prepared to experience lows near -5°F.
Below is a list of planting guides for Zone 6a.