It may be too late for this, but if the plant is rated hardy from zone 4 to 9 that doesn't mean it won't survive in your climate.* On the flip side, if a plant is rated as hardy to zone 9 and you live in a zone that is much colder, then it won't survive outdoors year round for you.* I live in zone 7 and have many plants that thrive in warmer zones.* The idea of the zones is to give you an idea of the average coldest temps the plant will survive in.
I used to live in the Catskills, so I'm familiar with your climate.* Sometimes you can actually push the zones by creating a micro climate.* If you live in zone 5 and you plant in an area that is close to a sunny stone wall or brick building, you might be able to push the zone by one and have something that would only thrive in zone 6 survive in your zone 5.* A thick layer if mulch can also be helpful.* I've seen people cover some of their plants with evergreen boughs too.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.