Screening of optimal harvesting period and drying methods for Paeoniae Radix Rubra based on eight bioactive compounds and biomass

Objective To identify the optimal harvesting age, timing, and drying method for Paeoniae Radix Rubra in Tongliao, Inner Mongolia, China. Methods The plant traits, biomass, and contents of eight pharmacodynamic substances were measured in 3-, 4-, and 5-year-old cultivated Paeonia lactiflora Pall. plants. 5 drying methods were applied to the roots of 4-year-old root. The bioactive components were quantified, followed by comprehensive evaluation using the CRITIC method and correlation analysis. Results The comprehensive evaluation of yield and quality showed that 4-year-old plants scored the highest at 0.5, followed by 3-year-old plants at 0.47, while 5-year-old plants scored the lowest at 0.4. Regarding the harvest time for 4-year-old plants, September 26 yielded the highest score at 0.87, followed by October 16 at 0.46, whereas September 11 received the lowest score at 0.41. Among the drying methods, shade drying resulted in the highest quality, ranking as follows: shade drying > step-down drying (105–80 °C) > high-temperature drying (>80 °C) > sun drying > low-temperature drying (60 °C). Correlation analysis revealed a significant positive correlation between paeoniflorin content and root dry weight across different harvesting ages. Additionally, paeoniflorin showed significant positive correlations with the contents of catechin, oxidized paeoniflorin, and lactiflorin across different harvesting dates. Conclusion The present findings are specific to Tongliao City, Inner Mongolia, and are not universally applicable. In this regional context, the optimal harvest period for Paeoniae Radix Rubra falls in late September of the fourth growing year, and shade drying proves to be the most suitable post-harvest processing method.