Aims <p>Cadmium (Cd) accumulation in leafy vegetables poses critical food safety risks. Although silicon (Si) is known to mitigate Cd toxicity, its intrinsic chemical mechanisms distinct from non-specific pH effects remain elusive.</p> Methods <p>Rapeseed (<i>Brassica campestris</i> L.) plants were grown in Cd-contaminated soil under four Si treatments (0–120&#xa0;mg·kg⁻¹). We evaluated ecophysiological responses (growth, antioxidant enzymes, Cd chemical forms) and quantified soil Cd bioavailability and free Cd²⁺ using diffusive gradients in thin films (DGT) and the Donnan membrane technique (DMT).</p> Results <p>In the rhizosphere, Si acted as a selective regulator, reducing free Cd²⁺ activity by 69%, thereby severing the primary exposure pathway. Concurrently, Si promoted intracellular Cd sequestration into inert residual fractions, limiting translocation to edible parts. This reduced the metabolic cost for detoxification, allowing the plant to redirect energy toward biomass accumulation (&gt; 109% increase), ensuring yield alongside safety. Furthermore, we validated a synergistic Genotype × Management strategy, where coupling Si with low-accumulating cultivars reduced leaf Cd levels to 0.06–0.09&#xa0;mg·kg⁻¹, significantly below the food safety threshold.</p> Conclusions <p>This study establishes a scalable solution for safe vegetable production, providing a scientific basis for pre-harvest hazard control in Cd-contaminated soils.</p> Graphical Abstract <p></p>