Kelp forests provide important ecosystem functions along rocky European coastlines, but they are threatened by ocean warming. In this context, we have been trying to understand the adaptive potential of Laminaria digitata (Hudson) J.V. Lamouroux towards temperature. In a first experiment, we investigated fast artificial selection of heat-tolerant gametophytes in a sublethal heat stress experiment. Two sets of gametophytes (pre-selected through a first heat treatment and non-selected control) were exposed to the same heat stress experiment ranging from 15 °C to 25 °C over two weeks. During the heat treatment, we assessed gametophytes survival and ontogenic development. After a recovery period of two weeks at 15 °C, we quantified sporophytes recruitment. Gametophytes did not survive better but showed a higher recruitment capacity which can be interpreted as an adaptive response or an artefact due to higher number of males which increases reproductive success. Then, a second experiment was designed to investigate how thermal history of gametophytes affects recruitment (carry-over effects within the gametophyte generation) and growth of juvenile sporophytes in a temperature gradient (cross-generational effects). By fertilizing gametophytes from cold (5 °C) and warm (15 °C) long-term cultivation (3 years) at 10 °C, we followed gametogenesis for two weeks. Then, sporophytes recruited were transferred to a temperature gradient spanning the tolerance of the species (from 0 °C to 20 °C) with the hypothesis that warm gametophyte temperature history promotes development of sporophytes at warm temperature. We discovered that gametogenesis speed and success is promoted by cold history of gametophytes. Moreover, cold temperature enhances performance of Laminaria digitata sporophytes at the extreme temperatures (0 °C and 20 °C) by cross-generational effects between gametophytes and young sporophytes. In the future, a cold season may be crucial to develop sporophytes with a wider thermal performance range, especially in regions where populations are close to their physiological thermal limit.