Think of seed bombs as an explosion of color thrown in neglected dirt areas to bloom. Seed bombs are typically medium sized pellets made of clay or composite with seeds that require none or very little maintains. Plant bombs can be planted in the Spring, summer and early Fall. They can consist of wild flowers or herb seeds, anything that beautify bare areas really. There are many ways to create a seed bomb, and they are also known as seed balls or earth balls. Once these seed bombs are tossed in the desired areas and enough sufficient amount of water, and sunlight, dissolves the components, you could be looking at plants in as little as a month.
How to Make a Seed Bomb: 9 Steps (with Pictures) is a great instructable to create your very own seed bombs. Another great article is explained by  Science Matters.

How To Make Seed Bombs from Jacob Rivkin on Vimeo.