Also known as: Dog Branch · Fire Storehouse
Xu is yang earth holding 戊 (yang earth), 辛 (yin metal), 丁 (yin fire) — warm dry soil with autumn metal and a banked fire residue. Classically the 火庫 (fire storehouse). Symbolically the loyal dog at the gate after sunset: watchful, faithful, defending the household. Xu Day Masters typically display loyalty, conviction, willingness to defend principles, and a tendency to feel responsible for the people they accept as theirs.
Xu san-he with 寅 and 午 transforms to fire (寅午戌合化火), and six-unites with 卯 to fire (卯戌合火). Conflicted by 辰 (辰戌冲 — earth-storehouse opposition), and part of the 丑戌未 三刑.
The oracle-bone graph 戌 shows an axe-like weapon, which is why it is so easily confused with 戍 shù, to garrison, and 戊 wù, the fifth Heavenly Stem. The Shuowen Jiezi glosses it through 滅 miè, to extinguish, and describes the ninth month as yang grown faint, all things brought to completion, yang descending into the ground. The Records of the Grand Historian is blunter still: Xu is when the ten thousand things are wholly extinguished. The sovereign hexagram for the month is Bo (剝 Bō), five yin lines with a single yang clinging at the top.
As a month branch Xu is earth in command at the close of autumn, with metal cooling and water beginning to gather. It is where Bing fire and Wu earth reach their burial stage, which is the basis of the fire-storehouse name, and where Ren water reaches its capping stage. Read practically, Xu is dry earth holding a banked ember: it will feed fire readily and does little for water. For charts anchored on Yin, Wu or Xu it is also the canopy-star seat, associated in older texts with solitary or scholarly inclinations.
Fire storehouse is not the same claim as strong fire. By the ninth month fire has passed its season, and what Xu holds is a residue kept in dry soil, not a blaze. The loyal-dog imagery is likewise a zodiac layer rather than the branch's older sense, which turns on completion and extinction. Mao and Xu uniting into fire does not mean the wood is consumed — a six-union describes binding, not destruction. And in writing, 戌, 戍 and 戊 are three different characters with three different readings.
Beyond the fire frame, the Mao union, the Chen clash and the triple punishment already listed, Xu harms You and breaks with Wei. That Chen clash is earth against earth and storehouse against storehouse, which is why it is argued about more than most: at stake is whether the fire stored in Xu and the water stored in Chen are released for use or knocked loose and spoiled. Mao uniting with Xu into fire is the reverse case — wood bound by earth rather than set against it.
Xu attracts more than its share of disagreement. The heavenly-net and earthly-snare labels are assigned differently by different texts — some place them on Chen and Si, others on Xu and Hai — so any confident statement about which pair carries them is a school position. Whether the Chen–Xu clash is mild because both sides are earth, or consequential because both are storehouses, is likewise disputed. And whether the Ding fire inside Xu can be drawn out depends on which storehouse theory a reader has adopted.
The Xu month runs from Hanlu (寒露 Hánlù) to Lidong (立冬 Lìdōng) and contains Shuangjiang, the descent of frost. Pentad almanacs of the Yueling tradition note late wild geese arriving, sparrows said in the old figurative language to enter the water and become clams, and chrysanthemums showing their yellow — the last colour of the year. On the twenty-four mountain compass Xu lies in the northwest with Qian and Hai. The Xu hour, 19:00 to 21:00, is dusk settling into night, which the old almanacs pair with closing the gate and taking stock.
No. A storehouse marks where an element is put away at the end of its cycle. In the twelve-stage scheme Bing fire reaches its burial stage at Xu, so the branch holds a fire residue in dry earth and not active fire, and by the ninth month the season belongs to metal and earth. Traditional readings say the stored Ding fire becomes usable mainly when a fire stem appears above, when the Yin–Wu–Xu frame completes, or — in some lineages — when the storehouse is clashed open.
Both branches are earth and both are storehouses, so the pair is read differently from an ordinary clash. The question classical practice asks is not who wins but what becomes of the contents: whether the fire kept in Xu and the water kept in Chen are shaken loose for use or damaged in the process. Lineages split on this, some calling the clash mild because the two sides are the same element, others calling it consequential precisely because storehouses are involved.
They differ by season and by contents. Wei belongs to late summer and stores Ji, Ding and Yi — dry earth still hot from the year's peak, holding the remains of wood. Xu belongs to late autumn and stores Wu, Xin and Ding — dry earth that has cooled, holding autumn metal alongside a fire residue. Wei is read as heat retained; Xu as heat banked and put away, with metal now present in it.
No. A six-union in classical usage describes two branches binding to each other, not one destroying the other. Mao and Xu are listed as uniting into fire, and whether that transformation actually takes place is usually made to depend on whether the rest of the chart, especially the stems above, already supports fire. Without that support most practitioners read the pair as joined but untransformed, each branch still carrying its own element.
They differ by a single stroke inside the frame. 戌 (xū) is the eleventh Earthly Branch and has a short horizontal stroke; 戍 (shù) means to garrison a frontier and has a dot; 戊 (wù) is the fifth Heavenly Stem and has neither. Mixing them up changes a chart, since 戌 and 戊 belong to different cycles — one a branch, one a stem — even though both are counted as earth.