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The early summer days have given the grasses’ readiness to bloom a further boost: These days, the first grasses will begin to bloom in the lowlands. “This heralds the start of the main season,” says Maximilian Bastl, head of the Medical University of Vienna’s pollen service.
For by far the largest group of allergy sufferers—those who react to grass pollen—one of the most stressful phases of the year begins: from June until August, they may be afflicted by symptoms such as itchy eyes, sneezing, and respiratory problems.
And according to current forecasts, the intensity is also likely higher. Bastl explains why a more intense season is possible with the scattered but sufficient rainy days in March and April. “They greatly promoted the development of the grasses. The temperatures were also ideal for this.”
Overlaps with allergens
However, it is not uncommon for greater stress, especially at the beginning of the season. This is partly due to changes in some grasses’ willingness to flower due to higher temperatures. A good example is smooth oat, some of which is already flowering in Vienna. “It was one of the first grasses to do so last year,” the expert recalls.
The plant usually only dusts after bluegrass and tussock grass, which traditionally kick off the grass pollen season. “As two highly allergenic grasses, smooth oatgrass and tussock grass, flower at the beginning of the season, the symptoms can be more severe for those affected.”
Warmer winters and overlaps
Even if you might think so: “In fact, the grasses are generally not earlier, and the seasons are not more intense in a long-term comparison,” Bastl emphasizes. A long-term study in several European countries only showed this in 2024. The results of the individual countries are the same.
Increasingly warmer winters due to climate change mean that some plants’ flowering seasons start earlier, but only for individual species. “If, for example, the smooth oatgrass starts earlier, this does not bring the season forward, as other grasses traditionally flower.”
However, the fact that changing temperatures put plants under stress and they produce more pollen as a survival strategy is a phenomenon that ecologists have observed in some plant species. And this also has consequences for humans: More allergens are in the air.
Pollen: “Arriving” plants on the increase
However, new arrivals among the grasses also trigger allergies, so-called immigrant neophytes. “In urban areas, for example, there are already many heat-loving grasses that extend the season,” Bastl mentions dog’s-tooth grass, for example, which only blooms in July and August and is considered one of the main allergens in grasses in South Africa.
For some years now, allergy sufferers have also been reporting more severe symptoms here. Subtropical, summer-flowering ornamental grasses, which are often planted in urban areas, can also cause problems in midsummer and prolong symptoms, “especially in urban areas,” says Bastl. Their flowering period usually begins in July and extends into September. This applies, among other things, to the lamp-cleaning grass, switchgrass, and Chinese reed. Bastl mentions the common reed, which “can cause significant grass pollen flight until September” along the Old Danube or Lake Neusiedl.
It is currently impossible to predict how these warmth-loving new arrivals will spread. “However, it can be assumed that they will continue to gain relevance for allergy sufferers in Austria in the future due to global warming.”
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