The last frost date generally occurs in late April. Like nature, this is variable and has occurred as late as the first week of May.
The first frost date generally occurs in early October but can occur later in the month.
USDA Zone 5 leans more toward hardier plants that can survive the longer winters and lower temps. We carry a limited selection of items that work well for this zone, but many of the varieties we carry work well as container plants that can be brought in during cold periods.