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Background: Rheum tanguticum Maxim. ex Balf is one of the plants generically known as rhubarb, a culinary vegetable that has long been used as a herbal remedy both in China and Europe. Increasing demand for rhubarb has triggered the overexploitation of Rh. tanguticum. Cultivation is therefore necessary for quality control and protection of wild resources. Nitrogen fertilizer plays an important role in cultivation. This study aimed to explore how nitrogen fertilizer affects the growth and quality of rhubarb on the Qinghai‐Tibetan plateau. Results: Nitrogen fertilizer promoted growth but had no significant influence on the active compounds of Rh. tanguticum. Generally, the N2 (150 kg ha−1) and N3 (225 kg ha−1) levels showed the most improved growth indexes, with no significant differences between them. The growth index and the amounts of eight of the nine studied active compounds in Rh. tanguticum increased from each year to the next and differed among growth stages. The contents of the active compounds were higher at the green stage and lower at the growth stage, which was opposite to the seasonal trends in root dry matter ratio. Gallic acid levels decreased with the growth of the plant. Conclusion: The N2 level (150 kg ha−1) was the recommended nitrogen fertilizer level in this study. It was revealed that seasonal changes rather than nitrogen fertilizer influenced active compounds in the root of Rh. tanguticum. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]