Earth occupies the centre of the Wu Xing rather than a point on its circuit, and some classical diagrams place it in the middle of the other four rather than between them in sequence. In the generative, or Sheng, order Fire's ash feeds Earth, and Earth in turn feeds Metal, its ore drawn from the ground. In the controlling, or Ke, order Earth controls Water, damming and absorbing it, while Earth is itself controlled by Wood, whose roots break the soil. Earth is therefore both a stage in the sequence and, in the centred reading, the pivot the other four phases turn around.
In Chinese medicine Earth governs the Spleen and its paired Stomach, and by extension the mouth, the flesh, and the transformation of food into usable energy; an Earth imbalance shows as poor digestion, worry, or the pensiveness the phase is said to carry. Earth's season is late summer or the turn of each season, its direction the centre, and its colour yellow, correspondences that place it at every transition rather than at one fixed point of the year.
Because Earth feeds and is fed by every neighbour in a centred reading, practitioners of five-phase diagnosis treat a weak Earth as a systemic risk: a Spleen unable to transform food starves every other organ of the nourishment the whole cycle depends on.
Sources Science and Civilisation in China, Volume 2: History of Scientific ThoughtJoseph Needham with Huangdi Neijing (The Yellow Emperor's Inner Classic)Traditionally attributed to Huangdi; actual authorship unknown