In the five phase system that organizes classical Chinese cosmology, medicine and calendar keeping, spring is the season paired with the phase Wood, the phase whose defining behaviors, in the oldest surviving definition from the Hongfan chapter of the Book of Documents, are simply that it bends and it straightens, an image of directed, upward growth rather than a fixed substance. Spring's yang energy is described as rising rather than dominant, still building toward the fullness it will reach at summer, and the season is read as the year's point of germination, when dormant potential from the preceding winter first pushes upward and outward into visible growth.
Chinese medicine extends the correspondence into the body, pairing Wood and spring with the liver and its paired organ the gall bladder, and with the emotion anger, understood in that framework not as a symptom to suppress but as the season's characteristic energy expressed, for better or worse, through this particular organ system; classical medical texts describe spring as a season for supporting the liver's smooth, unobstructed flow, an idea expressed in dietary and lifestyle guidance across the tradition rather than in any single fixed rule. The generating cycle of the five phases holds that Wood feeds Fire, so spring is read as the season that builds toward summer's fuller flowering, while the controlling cycle holds that Wood restrains Earth, giving spring's rising energy a checking role over the pivot phase associated with the turn of each season.
Sources Astrology and Cosmology in Early China: Conforming Earth to HeavenDavid W. Pankenier with The Foundations of Chinese Medicine: A Comprehensive TextGiovanni Maciocia