Biomass seedling containers were prepared from agricultural field wastes (i.e., rice straw and corn stalk) and cow manure, mixed with a starch adhesive. Based on the ratio of raw materials, different models of seedling containers were designed and tested. The performance of the seedling containers was characterized by measuring their forming ability in the mold, water absorption, air permeability, density, and various physical and chemical properties. The results showed that the percentage of well-shaped containers formed in the mold could reach as high as 98% when the ratio of rice straw to cow dung was 1:15, and the moisture content of the containers was approximately 15%. As the straw or stalk content increased, the percentage of seedling containers having good shape and compactness decreased, whereas the air permeability and water retention values increased. At the same mixture ratio, rice straw seedling containers were better than corn stalk seedling containers. The nutrient content of the seedling containers was over 10 times that of the soil surrounding the container, which could contribute to the conservation of soil fertility, as well as the seeding and transplanting of species in the process of ecological restoration.