Sweet sorghum (Sorghum bicolour), a native tropical C₄ crop, has attracted interest as a bioenergy crop in northern countries due to its juice-rich stem and high biomass production. Little is known about the traits important for its adaptation to high altitude climatic conditions and their genetic controls. Recombinant inbred lines derived from a cross between a sweet and a grain kaoliangsorghum were used in five field trials in Denmark and in China to identify the stability and genetic controls of morphological, biomass and biofuel traits during three consecutive summers with short duration, cool temperatures and long days. Eight out of 15 traits were found with high broad-sense heritability. Strong positive correlations between plant height and biomass traits were observed, while Brix and juice content were under different genetic controls. Using newly developed PAV (presence and absence variant) markers, 53 QTLs were detected, of which 18 were common for both countries, including a locus controlling stem juice (LOD score = 20.5, r ² = 37.5 %). In Denmark, the heading stage correlated significantly with biomass and morphology traits, and two significant maturity QTLs detected on chromosomes SBI01 and SBI02 co-localised with QTLs previously associated with early-stage chilling tolerance, suggesting that accelerating maturation might be a means of coping with low-temperature stress. Our results suggest that selection for tall and fast maturating sorghum plants combined with high Brix content represents a high potential for breeding bioenergy crop for Northern Europe.