Seedling trays are ideal for cultivating young plants. They are completely biodegradable and eventually decompose with soil if added on the ground. As the seedlings flourish transplant the seedling tray or individual pots directly into the ground and cover with soil. This will help protect the roots and develop strong plants. Once the trays start to decompose it will convert in to humus, which enriches the soil. Seedling trays are suitable for all types of seeds. And they are also great for gardeners who need to propagate heirloom seeds or hard-to-find varieties.