水泉 (suisen) here means a natural spring rather than a garden pond — groundwater that stayed frozen through the coldest weeks now begins, almost imperceptibly, to move again underground. Nothing about this is visible from the surface, and the genuinely coldest stretch of the entire year — late January into early February — is still ahead. But something has already shifted below ground, a full month or more before anyone above it would notice a change in the weather.
It's the direct counterpart to 閉塞成冬 (Sora samuku fuyu to naru), the first kō of Taisetsu back in early December, which described heaven and earth sealing off from each other as winter set in. This kō is that seal's first, quietest crack — 動 (ugoku, "to move, to stir") standing in deliberate contrast to 閉塞 ("sealed shut") from five kō earlier.
Still very good, past its sharpest peak but far from finished.
Winter shijimi (寒蜆, kan-jijimi) are prized for their concentrated flavor — good simply in a light miso soup.
Later-season fruit continues to be widely available and reliably sweet.
Still central to winter cooking, sweet and abundant.
Deep in season, excellent long-simmered or grated raw.
Fukujusō's bright yellow flowers open low to the ground, sometimes pushing straight up through a thin crust of snow — a plant whose Japanese name literally means "good fortune, long life," which made it a favored New Year gift plant in the Edo period despite blooming a few weeks past the New Year proper.
Miso, soy sauce, and sake are traditionally started during precisely this thirty-day 寒 (kan) stretch, when cold water carries fewer microorganisms and fermentation proceeds slowly and evenly rather than racing out of control. Sake made this way was historically called 寒酒 (kanshu), refined into something close to its modern form by Edo-period brewers in Itami, and miso brewed now — 大寒仕込み when timed to Daikan specifically — is prized for developing a deeper, rounder flavor with less raw saltiness than miso made in a warmer season.
"Water of the ninth cold day" — Water drawn specifically on the ninth day after kan no iri was traditionally considered the most potent of the entire cold season — believed to resist spoiling longer than water drawn any other time of year, and used preferentially for brewing, for pounding mochi, and for bleaching cloth.
動 (dō/ugoku) means to move or stir, chosen deliberately against 閉塞 (heisoku, "sealed shut") from 閉塞成冬 five kō earlier — the same underlying cosmology of heaven and earth's energy separating in winter, now shown reversing at its very earliest, most tentative stage.
Several Japanese miso makers sell kanjikomi kits timed to this exact window — a way to actually participate in the custom rather than just read about it.
Many regional breweries schedule their highest-grade batches for precisely this cold stretch and welcome visitors during the process.
"Spring water, flowing through a country with no mountains at all."
Whether miso, umeboshi, or a simple pickle, the same lower-microbial-activity logic that favors commercial kanjikomi applies just as well to a small home batch.
This kō marking an underground thaw doesn't mean the hardest cold is over — late January into early February is still ahead of you.
Buson's poem is technically about a season not yet arrived — the visible spring melt this kō is only just beginning, invisibly, underground. But that gap is the point: this kō describes water moving before there's anywhere obvious for it to go, in a landscape that doesn't yet look any different at all. What's already quietly underway in your own life, weeks or months before it'll be visible to anyone standing where you are right now?