Hi Peter, 

It is important to keep in mind that the USDA hardiness map zones are based on average annual extremes in temperatures and are not a guarantee. It is likely safe to try zone 5a compatible plants, but you will need to keep in mind that those plants will likely still need extra winter protection, and even with the USDA hardiness map being updated there is no guarantee that you will not get temperatures below that range. 

The hardiness zones are meant to provide a guide to what will likely survive in certain areas, so likely you will be okay with planting zone 5a plants, but take that information with a grain of salt and be prepared to protect those plants and see how they do over time. There are still colder areas and microclimates within a zone and weather patterns can be unpredictable. 

I would suggest starting out with a small amount of zone 5a plants and seeing how they do, before committing to a large amount of these plants in case they do not do well in your particular location. 

I hope this and the additional resources below are helpful.

Thank you, 

Protecting trees and shrubs in winter | UMN Extension

New 2023 USDA Hardiness Zones Explained | Extension (unh.edu)