Flowering time is a complex trait and has key role in crop yield and adaptation to environmental stressors such as heat and drought. The aim of this study was to better understand interconnected dynamic of epistasis and environment and look for novel regulators. For this purpose we investigated 534 spring barley MAGIC DH lines for flowering time at various environments. Analysis of QTL, epistatic interaction, QTL × environment (Q×E) and epistasis × environment (E×E) interactions were performed with single SNP and haplotype approaches. In total, 18 QTL and 2,420 epistatic interactions were detected including intervals harboring major genes such as Ppd-H1, Vrn-H1, Vrn-H3 and denso/swd1. Epistatic interactions found in field and semi-controlled conditions were distinctive. Q×E and E×E interactions revealed that temperature influenced flowering time by triggering different interactions between known and newly-detected regulators. A novel flowering-delaying QTL allele could be identified on chromosome 1H (named “HvHeading”) that was shown to be engaged in epistatic and environment interactions. Results suggest that investigating epistasis, environment and their interactions, rather than only single QTL is an effective approach for detecting novel regulators. We assume that barley can adapt the time of flowering to the environment through alternative routes within the pathway.