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Kurume group) are susceptible to environmental stresses such as drought, high temperatures, and soil physical and chemical conditions. We inferred that this susceptibility depends largely on their rooting potential. The rooting rate, the number of new roots, and root regenerating potential (RRP) obtained by incubating lignified root cuttings deteriorated remarkably or reduced during June and August. During summer, rooting did not respond to 1-naphtyleacetic acid (NAA) application. Reserve carbohydrates in the xylem tissue almost disappeared during June and August. These facts suggest that the rooting potential of root systems was distinctively low during summer. New root formation was inferred to be dependent on physiological conditions of parental roots, not only on external stresses, such as drought and high temperatures. In Kurume azalea, seasonal variation in rooting potential might be a major factor determining damage by environmental stresses