This study investigates, under field conditions, whether silicon (Si) addition reduces the accumulation of Cd and As in the edible parts of potato, carrot, onion, and wheat plants. Plants were grown in commercial plantations on alum shale soil in Hedmark County, Norway. Silicon, 500 kg per ha, was added in several forms for comparison: 1) potassium silicate solution, 2) Microsilica, an amorphous SiO2, and 3) Solaritt, a mixture of CaSiO3, Ca3Si2O7, and CaO. The concentrations of Si, Cd, and As were analysed in the edible plant parts and in the total and available soil fractions. Results indicate that Si addition increased the Si content by 12-28 % and reduced the Cd and As contents by 10-25 % and 20-40 %, respectively, in the edible parts of all investigated plants. In the soil, available Si increased up to 10-fold with Si addition while available As and Cd did not change. Potassium silicate and Microsilica had the highest effects due to the high plant availability of their Si content in soil. We conclude that increased plant-available soil Si reduces the As and Cd contents in edible parts of the investigated species and is not due to decreased As and Cd availability in the soil.