Price and quantity data prove that Irish potatoes in the 1840s were not Giffen goods. Intertemporal trade‐offs required by the fact that a sizable fractiono of the potato crop is needed for seed crops can produce unusual market dynamics. The Irish experience is well described by a normal demand model in which a permanent decline in the productivity of seed potatoes was at first mistaken as a transitory crop failure. These mistakes provoked “oversaviong” of seed crop in a population in dire circumstances. With the benefit of hindsight, consumption of seed crop capital was warranted. Erroneous expecations of potato productivity by growers delayed necessary agricultural adjustments and contributed to the catastrophe later on.