Zaanstad lies in the peat meadow country north of Amsterdam, a landscape that is close to the opposite of a wooded city. The Wormer- en Jisperveld and the Kalverpolder are open, wet grassland cut through by ditches — one of the largest continuous peat meadow areas in western Europe. There are barely any trees except along the ribbon settlements and the dykes, where willow, alder and poplar follow the water.
For hay fever sufferers that means a strongly shifted year. The spring season of birch and alder exists, but its source lies largely elsewhere: that pollen blows in from Het Gooi, the dunes, or further afield. The grass season from May to July, by contrast, is entirely local and unavoidable, because the grass runs right up to the edge of the built-up area. The open, unsheltered landscape reinforces it: nothing breaks the wind, so pollen travels far. The North Sea is about ten kilometres away, so a firm westerly does bring the level down noticeably.