Allelopathic Effects of Some Organic Mulch Extracts on Seed Germination and Early Growth of Some Ornamental Plants

Mulches have significant environmental, aesthetic and functional benefits. However, there are arguments that some organic types of mulches prevent seed germination and the growth of plants due to their allelopathic effects. This study examined the allelopathic influence of the extracts of some organic mulches on seed germination percentage, and growth of the seedlings of some ornamental plants in two interrelated experiments. In the first experiment, allelopathic effects of six organic mulches including pine wood chips of the plane tree, pine cones, pine leaves, pine barks, sawdust,and grass clippings of Festuca arundincea were examined on germination and early growth of lettuce seeds as an indicator species. The second experiment was designed based on the results of the first experiment so that the extracts of the mulches with the lowest germination rates were selected and their effect on seed germination of five flowering plants of Alyssum maritimum, Celosia argentea, Tagetes sp., Zinnia sp. and Rudbeckia sp. were evaluated. The results showed that pine leave extracts had inhibitory effects on germination of lettuce seeds (in the first experiment) and also showed significant and strong inhibitory effects (P<0.01) on seed germination, radicle length, plumule length, plumule fresh and dry weights of all seasonal flowers. Based on these results, pine leaves after being released in the soil or after decomposition may act as a source of allelochemicals and should be used by care as mulch in landscaping at least if it is combined with ornamental plants.