Forecast

The first purple alder catkins are ready to flower!

Although the weather of the last few days did not suggest it, the catkins of the purple alder have clearly developed further. In thermally favoured locations in the lowlands, some of them have even reached flowering readiness.
This alder species is often planted as a park or street tree and is characterised by the fact that it starts flowering much earlier than its relatives, namely at Christmas time. The purple alder usually occurs in smaller populations than its naturally occurring relatives. As a result, the expected impact is usually limited to the immediate vicinity of the plants.
If the maximum daily temperatures rise to over 5 °C for a longer period of time in the coming days, the first, low levels of pollen count may already occur in the vicinity of purple alder. However, as the weather forecast for the Christmas holidays is predicting rather low temperatures and occasional precipitation, it is unlikely that Purple Al der will be present until the weekend.

The forecast model for the start of the alder/hazel season has also been running again for some time now and is already providing initial data on the start of flowering, which is expected to occur between the middle and end of January. However, these forecasts are currently still subject to a very high degree of uncertainty. The closer we get to the actual flowering period, the more precise the calculated data will be.

Forecast date: 2025-12-22

Note: The data shown here are model data for the expected start of flowering. For more detailed information on the expected pollen count, please refer to the text forecasts.