Does the Use of Perennials in Flower Beds Necessarily Imply Sustainability?

Green spaces are becoming increasingly important for cities due to the growing pressures of urbanization and climate change. Along with trees, shrubs, and lawns, flower beds are an important part of urban green spaces. The majority of flower beds in public spaces consist of annual and biennial flower species. Such seasonal flower beds feature eye-catching colors but require significant effort to maintain and manage. Compared to these conventional flower beds, those with herbaceous perennials are more ecologically effective and less costly to maintain, and therefore more sustainable. The aim of this research was to analyze flower beds with perennials in the public green spaces of the city of Zagreb and to develop a tool based on predefined criteria and indicators to evaluate the sustainability of flower beds. In the context of the research, sustainability meant appropriate selection of flower species based on environmental conditions (temperature, light, precipitation), species diversity, greater ground cover and extensiveness of maintenance. The research results showed that there were 327 flower beds with perennials planted in the ground. The constructed Flower Bed Sustainability Index (FBSI) showed that the majority of these perennial beds (56.3%) had a conventional character, as only 28.1% of the beds had a completely correct species selection. This result indicates that the use of perennials does not necessarily guarantee the sustainability of flower beds, since, as in the case of flower beds with seasonal flowers, it depends, among other things, on the correct selection of species adapted to local environmental conditions. The FBSI is shown to be a suitable tool for assessing the degree of sustainability of a flower bed and could be a useful tool in landscape design and management of such types of green spaces.