Soaking cereal seeds in β‐cyclodextrin solution for 1–3 days the germination process, development of shoots and roots is retarded strongly but reversibly. Retardation means a strongly reduced growth of the plant; the length of the shoots and roots is only 15–35% of that of the control (water‐soaked) plants in the first 6 days. The roots are not only shorter, but deformed, and their dry substance content is significantly higher. The absorbed cyclodextrin is metabolised in about 5 days, thereafter a more vigorous growing is observed. The height and dry mass of 4 weeks old plants developed from cyclodextrin‐treated seeds under laboratory conditions (in phytotron) are significantly higher than that of the control plants. The cyclodextrin‐treated cereals are more ramified, bearing more ears. In phytotron experiments a surprising crop yield increase was observed. In preliminary plough‐land experiments more modest, nevertheless promising results were obtained. Cyclodextrin‐treatment reduces the sensitivity of the plants against the phytotoxic effect of herbicides. There are various hypotheses for the explanation of the observed phenomena, but neither of them is supported yet with experimental proofs.