Our results indicate that root hair formation is strongly dependent on exuded SL and/or the presence of active transport of SL by PDR1 through the epidermal layer. Our time‐lapse analyses showed that PDR1 is active from initiation to full elongation of each root hair. As SL was reported to regulate cytoskeletal dynamics (Pandya‐Kumar et al., 2014), we suggest that the extra SL transported by PDR1 allows an extended development of root hairs. We observed a reduced SL concentration within PDR1 OE roots, while pdr1 mutants, which have shorter root hairs compared with the wild‐type, were shown not to differ from the latter in root internal SL concentrations (Kretzschmar et al., 2012). These observations indicate that the PDR1‐triggered SL release into the rhizosphere probably has a stronger impact on root hair formation than does internal SL redistribution.