During etiolated growth of the Arabidopsis hypocotyl, all cells initially grow synchronously at a slow pace and then growth acceleration takes place only in cells located at the base of the hypocotyl. Although several growth-regulatory key players have been identified, the regulation of hypocotyl elongation remains elusive. Zdanio et al. (on pp. 1192–1204) have identified EXTENSIN33, an ER and cell wall-localised protein that controls the rate and extent at which hypocotyls grow in the dark by modifying cell wall extensibility.