ARS compiles official ratings for every commercially available rose and publishes them in its Handbook for Selecting Roses, a booklet sent free to members. These ratings are a national average based on overall performance, taking into account the variety's vigor, disease resistance, flower form, and quickness of repeat bloom. Because some roses grow better in certain regions than in others, you must keep this in mind when studying ratings. For example, in Shreveport, Louisiana, the "Shreveport" rose would achieve a rating of Excellent to Outstanding. However, its official rating is Good, because its overall performance is less exemplary in other parts of the country.
Although it offers no guarantees, the ARS rating is a useful guideline for predicting the success of a rose. In general, the higher the rating, the more satisfactory the rose. If you wish to avoid disappointment, don't purchase a rose rated lower than 7.0 unless the variety has some special virtue that offsets its low rating. Nursery catalogs rarely give ARS ratings, so it is helpful to obtain a copy of the handbook.