The Wachau is at its most spectacular twice a year: in late April when the apricot trees are in full blossom (the valley is one of the largest apricot-growing areas in Austria) and in September and October during the wine harvest, when the vineyards are heavy with grapes and the Heurigen are busy serving the new vintage.
July and August are the busiest months, with large numbers of day-trippers and cyclists. The boat service is most frequent then, and all the Heurigen and restaurants are open. Winter is quiet — several wine taverns close, the boats stop running, and the valley has a grey, dormant quality. The Advent markets in Krems and Dürnstein are pleasant exceptions.
The main risk in any season is rain, which makes cycling on the gravel sections less pleasant but does not spoil the wine-tasting aspect of a visit at all.