Background  Herbs can reinforce a large number of exposed slopes left by construction work of roads, railways and mines and other projects. It also improves their ecological environment. In comparison of the shrub seeds, the herbaceous seeds germinate and grow more rapidly. Moreover, the herbaceous seeds are more competitive than shrub seeds in herb-shrub mixed type, which is the target community in the slopes greening. The application of plant growth retardants in lawn conservation is more extensive. However, there are few studies on the soaking treatment of herbaceous plants in slope greening. Therefore, it is necessary to develop the study of plant growth retardants to inhibit the germination of herbaceous seeds.

Methods  In this paper, Astragalus adsurgens, Medicago sativa and Festuca arundinacea, that are widely used in slopes greening in North China, were selected as the test materials. Chlormequat, uniconazole and paclobutrazol were chosen as test retardant reagent. A seed soaking experiment was carried out by using different density and kind of above three plant growth retardants. Firstly, three herbs seeds were soaked in different concentrations of chlormequat, paclobutrazol and uniconazole solution. Then three seeds were taken out, washed and placed in a constant temperature incubator within 15 days. Finally, the germination energies of three herbs and their effects of radicle and embryo growth were analyzed.

Results  For A.adsurgens, the optimal paclobutrazol soaking concentration were 300-500 mg/L, and optimal chlormequat soaking concentration was 100 mg/L. For M.sativa, the optimal paclobutrazol soaking concentration was 480 mg/L, and optimal uniconazole soaking concentration was 320 mg/L. For F.arundinacea, the optimal chlormequat soaking concentration was 520 mg/L, and optimal paclobutrazol soaking concentration was 420 mg/L. Chlormequat and uniconazole solution reduced the ratio of germ length of A.adsurgens and M.sativa, and increased the ratio of radicle length. The germination energies of the three herbaceous seeds were inhibited by the 300-400 mg/L paclobutrazol solution. The germination energies of A.adsurgens and F. arundinacea were inhibited by 500 mg/L uniconazole solution. The inhibitory effect of chlormequat solution on the germination energy of M.sativa and F.arundinacea was significant. And the higher the concentration of chlormequat solution, the stronger the inhibitory effect on the length of their embryo.

Conculsions The inhibitory effect of paclobutrazol on the germination energy of A.adsurgens, M. sativa and F.arundinacea was significant, and also inhibited the germ length of A.adsurgens and M.sativa. Uniconazole had a significant inhibitory effect on A.adsurgens and F.arundinacea. Therefore, three plant growth retardants inhibited the germination of three herbaceous seeds, which provides reference index for plant growth retardants to treat herbaceous seeds in slopes greening.