Maastricht is the southernmost city in the Netherlands, and for hay fever that is no footnote. Spring arrives in South Limburg before anywhere else in the country, and the trees follow: in a mild winter hazel and alder can flower here in the first half of January, weeks before anything happens in Groningen. If you have symptoms in Maastricht while the national reports still read quiet, you are usually not imagining it.
The landscape differs from the rest of the country too. On the loess soils of the Heuvelland, hill forests carry beech, oak and a great deal of hazel, while alder and willow line the water in the valleys of the Jeker and the Meuse. The Sint-Pietersberg and the Savelsbos are within walking distance of town. Maastricht is also wedged between Belgium and Germany: an easterly or southerly brings pollen from the Ardennes and the Rhineland, both far more wooded than the Netherlands itself. The grass season runs from May into July, sourced from the meadows of the Meuse valley and the hill country.