Boron (B) toxicity is a relevant problem in Mediterranean regions, where irrigation water may present high concentrations of this micronutrient. In this study, the potential of aqueous extracts from the brown macroalga Laminaria digitata and the diatom Phaeodactylum tricornutum, applied alone or in combination with metalloids (Se, Si) and micronutrients (Mn, Fe, Zn), was evaluated to improve the tolerance of tomato plants (Solanum lycopersicum L.) grown under excess B (15 mg L⁻¹). The extracts were applied foliarly, and growth parameters, gas exchange, chlorophyll content, mineral composition, B accumulation, oxidative stress, and metabolic profile were analyzed. Excess B significantly reduced root development, net photosynthesis, and metabolic balance, evidencing a strong physiological impact. The application of algal extracts partially mitigated these adverse effects, mainly through improvements in photosynthesis, water use efficiency, and the accumulation of osmoprotective metabolites (proline, tryptophan, glucose). In particular, L. digitata promoted a significant increase in total biomass and greater physiological recovery compared with P. tricornutum. Conversely, formulations enriched with metalloids and micronutrients did not provide consistent additional benefits and even induced metabolic imbalances. Multivariate analysis (PCA) confirmed that relative tolerance was associated with physiological and metabolic variables rather than nutritional changes. Overall, these results highlight the potential of algal extracts, especially L. digitata, as effective biostimulants to mitigate boron toxicity in tomato.