The occurrence of Teucrium scordium in a dune slack on the Isle of Voorne was studied over a series of years. The locality was divided into 2 x 2 m² plots and the presence of T. scordium was registered by counting stems (both flowering and non-flowering) and by making vegetation analyses. The amount of rain and the height of the ground water-table were recorded. It is concluded that the species retreats in dry years and expands in wetter years.