This study was conducted to evaluate four hybrid poplar comparison tests along a groundwater availability gradient in Western Slovakia. The weather fluctuation during the 3-year study period was described with indices, such as the Forestry Aridity Index (FAI) or the hydrothermal coefficient (HTC). The soil chemical and physical parameters were determined from soil samples from the two upper horizons. The nutrient status and supply of the trees were categorized based on leaf elemental analysis. Altogether, 21 different clones from 6 genomic groups were compared. The survival (SRV), diameter at breast height (DBH), and height of the trees (H) had been measured annually since the plantations were established, and from these measurements, mean annual height increment (MAHI) values were derived. These weather, edaphic, and clonal factors were evaluated and compared. Significant effects of the site (edaphic factors) were found as the primary source of variance and clonal differences as secondary sources of variance among the growth of trees. The interaction of site × clone effects was not significant. The results showed that for short rotation forestry (SRF), the site parameters—especially groundwater availability—are key factors.