In Germany in 1951–2025, tree leaf-out and fruit-tree flowering moved earlier by 2.1 days per decade and the last −2 °C frost by 1.3 days, but frost after onset did not increase significantly

Question: did warming increase late-frost exposure of new leaves and open fruit-tree flowers in Germany? We used 1,256,680 DWD phenology records (1951–2025) of leaf-out of 7 tree species and flowering start of 4 fruit trees, with daily minimum temperature (Tmin) from the 1-km HYRAS-DE grid at each station. For each station-year we found the last spring frost (last day before 1 July with Tmin ≤ −2 °C) and the margin (onset minus last frost). Station fixed-effect year effects and Newey–West trend errors make the year the unit of uncertainty. Leaf-out moved earlier by 2.08 days per decade (95% CI 1.50–2.65) and fruit flowering by 2.13 (1.33–2.93). The last frost moved earlier by only 1.28 days per decade (0.21–2.34). Thus the margin decreased by 0.80 days per decade (−0.24 to +1.84), in the same direction for 10 of 11 taxa. The share of leaf-out records with frost after onset was 17.6% in 1951–1987, 20.4% in 1988–2017 and 26.6% in 2018–2025. But the trend (+1.2 points per decade, −0.2 to +2.6) falls to +0.5 without the frost years 2017 and 2024. Fruit flowering gave similar results. Station Tmin from 181 long DWD climate stations gave the same trends for the same records. At phenology sites the last frost moved earlier by less than a uniform shift of the seasonal Tmin curve predicts (−6.1 vs −10.6 days, 1951–1980 to 1996–2025), but station data at 80 climate stations did not confirm this lag (−8.1 vs −10.2 days; difference CI includes zero). Margin decreases were not significantly different between low and high stations. Limitations: 75 years with rare frost events cannot confirm or exclude a change of about 1 point per decade; 2-m air Tmin and a −2 °C threshold are an index, not damage; fruit varieties are not controlled; Germany only.

late spring frost · false spring · phenology · leaf-out · fruit tree flowering · climate change · Germany · DWD · HYRAS · frost risk · safety margin