Eindhoven stands on the sandy cover soils of the Kempen, and that thin dry ground decides what grows. Birch is a pioneer that thrives precisely on poor sand, and it is everywhere around the city: in the Genneper Parken, along the heath, on the old reclamations. On top of that the Dommel and the Tongelreep run straight through town, with alder carr in their valleys — and alder is the first to flower, often as early as January.
The second half of the year is agricultural. Eindhoven is ringed by farmland where cereals are grown alongside grass, and of the cereals rye is the one that genuinely troubles hay fever sufferers, with a short peak in late May and June. Together with the grass season that makes late May to mid-July the heaviest stretch. Eindhoven also lies far from the sea, so the dilution by clean maritime air that coastal cities enjoy is largely absent; on a still, dry day the local pollen level can build up considerably before anything is carried away.