The Jianghan Plain is the core cultivation area of southern black poplar. Cuttage afforestation and afforestation with roots are the local main afforestation methods, but the difference in long-term growth rhythm is not clear. In order to scientifically select afforestation methods and support efficient cultivation of poplars, four black poplar varieties of ‘Danhongyang’, ‘Huashi No.2’, ‘Chulin No.2’, and ‘2025 Yang’ were used as test materials to carry out a continuous 8-year positioning comparison test, and systematically analyzed the diameter at breast height (DBH), total tree height growth and annual net growth rhythm of black poplar under the two afforestation methods. Statistical results showed that over the eight years of afforestation, the cumulative increments in DBH and tree height of four varieties planted by cuttage afforestation at different ages were all higher than those of afforestation with roots. Moreover, within the first two years after afforestation, the average growth rates of DBH and tree height of cuttage afforestation exceeded those of afforestation with roots by more than 21% and 13%, respectively. The variance analysis results indicated that there were highly significant differences in the total growth of DBH and tree height traits among both the afforestation methods and the varieties. The t-test results for the total growth of DBH and tree height under the two afforestation methods showed that all significant differences were attributed to the greater growth in cuttage afforestation compared to afforestation with roots. The t-test results for the annual net growth of DBH and tree height under the two afforestation methods revealed that, in the first two years, for all four varieties, the net increments of cuttage afforestation were significantly greater than those of afforestation with roots, except for tree height of ‘Chulin No.2’ in the second year. By the third year, there were no significant differences in the net growth of DBH and tree height between the two afforestation methods for any of the varieties. From the fourth to the fifth year, due to flooding stress, most varieties exhibited greater net growth in afforestation with roots compared to cuttage afforestation. From the sixth to eighth years, there was generally no significant difference in growth between the two methods. Overall, in the Jianghan Plain, excluding the impacts of prolonged flooding and extreme climates, the growth of black poplar under cuttage afforestation was significantly superior to that under afforestation with roots in the first two years. From the third year onward, the difference between the two afforestation methods became insignificant. The maximum annual net increment of DBH occurred in the second year after afforestation, while the maximum annual net increment of tree height appeared in the third year. The findings of this study can provide a theoretical basis for further selecting poplar cultivation modes and implementing efficient cultivation in this region.