Although there are numerous studies on the genetic control of flowering time in barley, little is known on the genetic control of duration of different particular pre-heading phases. Extending the stem elongation phase (SE), without modifying total time to heading, has been proposed as a trait to raise yield potential. Moreover, studying the genetic control of pre-heading phases would be of interest for a better understanding of crop phenology which is crucial for adaptation. We studied the genetic control of the leaf and spikelet intitiation phase (LS), the stem elongation phase, and within this, from the onset of jointing to flag leaf (J-FL), and from then to heading (FL-HD), in the Steptoe 9 Morex population, which is known to segregate for some major developmental genes, under different environmental conditions. After a preliminary greenhouse study in which the appropriateness of the population was tested, 130 double haploid lines and the two parents were grown under four field environments that differed in photoperiod and temperature conditions. Amongst all QTLs detected (13), only three were significant for HD and for both LS and SE and with the same allele direction (although with greater effects in one phase than the other in some cases). Genotype by environment interactions for LS and HD were due to both photoperiod and other factors as temperature or its interaction with photoperiod, while for SE responses to only photoperiod were negligible. QTL 9 E interactions were important for some QTLs, and either cross-over (e.g. Ppd-H1) or quantitative (e.g. Ppd-H2). However, heritability across field environments for the ratio SE/LS was high (0.8) and several of the QTL effects that were significant for only LS or SE, were conserved across different environments, that is, they were significant with the increasing allele derived from the same parent in all or most environments.