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Rice‐straw biochar enhanced soil nutrients contents except availability of N.Microbial community structures in soil were optimized after biochar application.Biochar (10%, w/w) improved growth of C. morifoliumRamat. ‘Hangbaiju’.Biochar increased the total flavonoid content in flower of ‘Hangbaiju’.Biochar reduced physiological P and K use efficiencies in ‘Hangbaiju’ plant. Soil acidification, fertility decline, and continuous cropping obstacles are detrimental to Chrysanthemum morifoliumRamat. ‘Hangbaiju’ growth. Biochar has been reported as a good soil conditioner. However, the mechanism by which rice‐straw biochar regulates soil chemical and biological properties and adjusts Hangbaiju growth needs to be elucidated. A field experiment was conducted in Tongxiang City, China, where Hangbaiju originated, to determine the effect of rice‐straw biochar on the characteristics of soil nutrient and microorganisms and on yield, quality, and nutrient use efficiencies of Hangbaiju. Significant increases were observed in total N content in soil and soil pH in all biochar treatments (5, 10, 15, and 20%, w/w), in NH4OAC‐extractable K and organic C content by the application of 10% or more rice‐straw biochar, and in Olsen P content by the addition of 20% biochar compared with that of no biochar application in soil (CK). However, alkali‐hydrolyzable N content was significantly reduced by 25.9 to 35.3% in all biochar treatments. Application of 20% biochar significantly increased the bacterial quantity of soil by 26.9% compared with that of CK. Applying 10% or more biochar significantly increased actinomycete quantity by 80.6 to 130% but decreased the number of fungi by 22.2 to 30.2%. Furthermore, Fusarium oxysporumin all biochar treatments was reduced by 42.4 to 54.4% compared with CK. Hangbaiju yield was greatest when 10% of biochar was added to the soil (23.9% higher than CK). However, larger amounts of biochar decreased yield. Biochar application increased the total flavonoid content in the flower of Hangbaiju compared with CK by 9.40 to 43.3%. However, biochar application decreased physiological P and K use efficiencies but caused a slight increase in physiological N use efficiency. Therefore, the application of 10% (w/w) rice‐straw biochar in soil is best suited to improve soil quality and increase the yield of Hangbaiju.