Ground-based vertical greening is one of the well-known nature-based solutions that is widely used in city centres due to its small footprint and the large surface area of vegetation. Although the impact of vertical greening on the local microclimate has already been extensively researched, there is a poor understanding of the impact of vertical greening on historic building fabrics. The impact of vertical greening on microclimate environments has primarily been researched through in situ case-study monitoring; as such, there are currently no standard protocols for investigating this impact in laboratory studies. By performing simulations in controlled laboratory conditions, the influence of vertical greening on specific environmental conditions can be assessed as well as the significance for key mechanisms, such as the insulation capacity of a vegetation layer. Experimental results on the insulation capacity of vertical greening illustrate that the presence of vertical greening reduces the rate of heat exchange between the wall and the surrounding environment compared to the bare wall, resulting in a delayed temperature response of the wall. This delay varies across the seasons or its intensity, which is represented, for instance, by a more pronounced delay in the wall’s surface temperature response in summer than in winter. However, the magnitude of the insulation capacity is more pronounced in winter (up to +2.1 °C) compared to summertime. The insulation capacity of vertical greening is more likely to have a significant impact on façades with a lack of solar irradiation, such as façades facing north or shaded by built surroundings. This experimental investigation can help build an understanding of these processes more fundamentally and support the interpretation of in situ case-study monitoring as well as provide a standardized approach to investigate the environmental performance of vertical greening across climatic regions and seasons.