Water deficiency and temperature extremes, exacerbated by climate change events, lead to depletion in plant physiology and fruitfulness in most part of the world. Studies demonstrated that foliar seaweed (SW) treatment can promote plant growth and mitigate the adverse effects of climate change. Therefore, the effects of SW spraying (0.5%) on grapevine physiology, vine yields and quality of ‘Alphonse Lavallée’ have been investigated under both full irrigation (FI; maintaining water holding capacity of soilless medium at 100%) and deficit irrigation (DI; irrigation amount at 50% of FI) conditions in soilless culture under glasshouse condition. Foliar SW treatments applied three times during vegetation significantly improved the stomatal conductance, leaf relative water content and leaf growth of vines for both irrigation conditions. In particular, shoot growth and vine yield of SW treated vines were remarkably higher than nontreated ones under DI condition. SW also improved the berry and cluster weights under DI. Berry detachment and skin rupture forces increased after SW pulverization in DI vines. SW in DI subjected vines also accelerated the berry ripening with increased soluble solid content. Overall, foliar SW treatment could be recommended for sustainable grape production under the effects of water deficit in the face of climate change.