Flowers in the wrong season

Cherry trees are blooming in December. Yarrow is flowering through November frosts. Across Europe, hundreds of plant species are producing flowers in months when they should be dormant. The dominant narrative of climate-driven phenological change - earlier springs, later autumns - cannot account for these events, because they fall outside the expected seasonal window altogether. Using over 31,000 citizen science observations from iNaturalist, I document off-season flowering (October through January) in 780 native European species and show that its frequency has roughly doubled since the mid-2010s. Two distinct mechanisms likely drive this pattern: disrupted winter dormancy in trees and shrubs, and opportunistic regrowth in herbaceous species that keep growing whenever conditions allow. Both are driven by the widening mismatch between rising temperatures and unchanging day length. I argue that phenology must now be assessed not only by when events occur but also by whether they stay within their expected season.