When growing small flower seeds use biodegradable egg trays. When the seedlings are ready for planting in the garden just pop the whole tray in the garden and cover tray with soil.
The cavities in egg crates are just the right size for starting many types of seeds. An added advantage to the paper style is that it can be cut apart and the seedling planted in the soil container and all. This is a page about egg carton gardening.