Every second year the ISU awards ISU-Diplomas to newly introduced perennials. Perennials that have not been on the market for more than five years are admitted for evaluation. As a rule the perennials are planted between one and two years in advance in an evaluation garden. During the Summer Days they are evaluated by an international jury.

The elected perennials will be given a diploma and presented in word and picture on the ISU homepage. A series of perennials that have been awarded in the evaluation of new introductions of the ISU, such as Agastache 'Blue Fortune', Salvia nemorosa 'Markus' or Sedum 'Matrona', have become a part of the standard assortment in nurseries worldwide.

The focus is on cultivation suitability and garden value of the perennials. Depending on the use (habitat), different properties may be sought-after. For boarder habitats, for example, we are looking for perennial plants that have a high ornament value, that are healthy and have a good aspect for as long as possible. The properties of the perennial plants are examined in special evaluation gardens.

One of the most important goals of the ISU is the co-ordination of perennial plant evaluation on an international level and the exchange of information and evaluation results. For this reason every two years a special evaluation meeting takes place on occasion of the ISU Summer Days.