Much of the Black Hills area falls into Zone 5 on the Cold Hardiness Zone map, a tool used by most gardeners to determine planting timelines and the types of plants that will fare well on their properties.
Many have enjoyed success with Zone 5 plant material for years, and reaped the joys of having a beautiful foliage or bloom to complement the staid Zone 3 and 4 plants that are the bones of western South Dakota gardens. The key to using the less hardy plants is to take extra precautions, to ensure that you have success.
Protection is the key to understanding the hardiness of plants. Exposure to the rain, wind and sun can reduce the hardiness of a plant by a full zone. Winter winds and cold/warm fluctuations endanger plants more than prolonged cold temperatures so a wise gardener will take note of these areas and use plants a zone colder and protect soil and plants with mulch.
In a protected area next to a foundation on a south side, then perhaps you can use plants a zone warmer than you normally would. In any yard it is possible to have areas that would be in three different zones. This can provide the opportunity to possible triple the amount of plants used in your landscape gardening plans.
Tender shrubs and perennials often require the extra effort of finding a good site or microclimate in your yard, soil amendments, meeting specific watering needs, and mulching. The summer climate in western South Dakota can be very dry and windy and the winters are often very cold with yo-yo temperatures and a complete lack of snow cover for late season. A 3-4" layer of mulch will help to even out temperature and moisture fluctuations. Additional mid-winter applications of straw, pine boughs or pine needles to a depth of 12" with help to prevent desiccation caused by winds and little snow cover.
Cold hardiness zones are relative to other factors besides just the average temperatures over the past 25 years. Snow cover, likelihood of early or late frosts, rainfall (moisture available to the plant) and protection all should be figured into the bigger picture when choosing plant material in any zone.