Almost five thousand allotment gardens divided into one million plots are used by roughly 10% of Polish society. Several studies have emphasized their social importance and significance for enlargement of the area and the integrity of urban spatial greenery systems. However, the area of allotment gardens in Polish cities has been decreasing since the changes in the post-communist country in the 1990s. There is a lack of a simple method of classification and valuation of allotment gardens in relation to their significance in urban green space systems that could be used by officials and city planners. Hence, this study aims to examine the significance of allotment gardens in the spatial development of the green space system of Poznań and classify them with a simple and universal method of valuation which could be used in urban planning. The location of allotment gardens in the urban green space system in Poznań was examined with the classification method elaborated here. It was based on the valuation of several internal and external features of individual allotment gardens. The results showed that allotment gardens are important areas and spatial elements of the green space system in Poznań. Over 30% of allotment gardens are of high significance in the green space system of the city. Nevertheless, according to urban planning documentation, there are plans to reduce the area of allotments in Poznań. Even gardens indicated in the research to be of high significance to the integrity and enlargement area of the urban green space system are planned to be liquidated. Use of the developed classification could influence the decision-making process regarding the liquidation of allotment gardens and preserve the most valuable objects.