Cellular elongation requires the defined coordination of intra‐ and extracellular processes, but the underlying mechanisms are largely unknown. The vacuole is the biggest plant organelle, and its dimensions play a role in defining plant cell expansion rates. Here, we show that the increase in vacuolar occupancy enables cellular elongation with relatively little enlargement of the cytosol in Arabidopsis thaliana. We demonstrate that cell wall properties are sensed and impact on the intracellular expansion of the vacuole. Using vacuolar morphology as a quantitative read‐out for intracellular growth processes, we reveal that the underlying cell wall sensing mechanism requires interaction of extracellular leucine‐rich repeat extensins (LRXs) with the receptor‐like kinase FERONIA (FER). Our data suggest that LRXs link plasma membrane‐localised FER with the cell wall, allowing this module to jointly sense and convey extracellular signals to the cell. This mechanism coordinates the onset of cell wall acidification and loosening with the increase in vacuolar size.