The classic selection of plants for landscaping the urban environment is a rather labor-intensive process involving the use of a large number of reference materials, atlases and plant catalogs. It is necessary to consider various characteristics of plants, taking into account their decorativeness, mutual compatibility, survival in the natural conditions of each region, etc. The purpose of the research was developing a polytomous key and creating it using a modern computer program to simplify the selection of plants according to decorative, phenotypic and phenological characteristics for landscaping cities in the southern Russia. The method of compiling a polytomous key was used as a way to identify plants by several leading characteristics, when the original groups were simultaneously divided into several smaller ones. The life forms, size, habitus of plants, characteristics of the trunk and crown, characteristics of flowering and fruiting, as well as environmental requirements were taken into account. On the basis of the research results the assortment of ornamental plants in large nurseries of the Krasnodar Territory and the Republic of Adygea, a list of plant names was compiled and their characteristics were encoded using a polytomous key. The key consisted of 8 sections, thanks to which it was possible to give the most complete description of the plant according to 36 parameters. The resulting database received state registration certificate No. 2023621905. The base and operation of the polytomous key are like a computer program. The functioning of the program has been successfully tested. The created program greatly simplifies the work of choosing an assortment of plants for landscaping, reducing it to a few minutes.