Aims <p>The roles of soil microbiota and water availability in regulating the biogeochemical and plant-related effects of enhanced silicate weathering (ESW), which can simultaneously remove atmospheric CO₂ and improve soil fertility, remain unresolved. This study aimed to determine how basalt amendment, microbial inoculation, and soil moisture availability interact to influence maize performance, nutrient dynamics, and soil processes.</p> Methods <p>A fully factorial outdoor mesocosm experiment was conducted using soil amended with basalt and inoculated with <i>Bacillus subtilis</i> under temporally differentiated soil water availability. Plant biomass, nutrient status, heavy metal uptake, and photosynthetic system responses were measured alongside changes in soil chemistry and water status.</p> Results <p>Basalt increased Si concentrations in maize kernels, leaves, and stems, with <i>B. subtilis</i> further enhancing leaf Si, indicating microbially mediated increases in rhizosphere Si availability. Basalt application also increased Mg, Ca, and P concentrations in specific tissues, while reducing leaf Fe, Mn, and Zn concentrations, coinciding with reduced chlorophyll content. A transient constraint on early plant growth suggested short-term stress during initial weathering, an effect partly alleviated by <i>B. subtilis</i>. Root biomass increased under low water availability and was further amplified by the combined basalt and microbial treatment. Soil moisture availability modulated the hydraulic responses associated with basalt amendment.</p> Conclusions <p>Overall, basalt and <i>B. subtilis</i> primarily influenced plant elemental composition and soil chemistry rather than aboveground biomass production, with their effects regulated by water availability and time. These findings underscore the importance of integrating biological and hydrological controls when evaluating silicate amendments in soil–plant systems.</p>