The “Réseau d'essais des plantes ligneuses ornementales du Québec” (REPLOQ) is a research project initiated in 1982 with the mandate to elaborate, develop, and coordinate a cooperative research project to evaluate the winter hardiness of ornamental plants. Systematic evaluation trials provided information on growth potential and hardiness of woody trees and shrubs evaluated over a 5-year period in the principal growing regions of Québec. Zonal range covered was 2 to 5b in the Canadian system. Adequate field testing is critical for new introductions and, since 1984, more than 400 species and cultivars have been introduced and eight evaluated in each climatic zone. Propagation methods, as well as their potential for ornamental purpose, were described. In the 1984 plantation, 30 ornamental species and cultivars were evaluated. Winter damage data observed on each plant during this period were analyzed by Clusters analysis and five groups of plants were determined. Trees, flowering shrubs, and foliage shrubs were discussed separately and winter damages of each group were submitted to “Correspondence analyses” to identify plant response to climatic conditions. Growth and production potentials were defined by SAS analysis. Hardiness zone of each species was detailed, established, or modified.