Our experiments were designed to investigate yield formation of intercrops and their influence on broadleaved weeds under organic cropping conditions. Pea (Pisum sativum L. (Partim) and spring wheat (Triticum aestivum L. emend. Fiori et Paol.), spring barley (Hordeum vulgare L.), oat (Avena sativa L.), and spring triticale (× Triticosecale Wittm.) were sown as intercrops (50:50 – a relative proportion of grain legume and spring cereal seeds) or as a sole crop. The results suggest that pea/wheat, pea/oat, and pea/triticale intercrops were superior to sole pea crop. However, intercrops and sole cereal crops exhibited similar weed suppression capabilities. According to the reduction of weed number and mass, the intercrops were ranked in the following order: pea/oat > pea/wheat; pea/triticale > pea/barley. Crop density significantly influenced the reduction of total weed numbers and air-dried mass. In crops with lower plant density, weed suppression depended on crop height.