This spring I've been hosting workshops where I've been teaching gardeners across Chicago how to make seed bombs. There are as many seed bomb recipes are there are gardeners. This is the method I like to use to make seed bombs at workshops because it's quick, easy and there's less mess to clean up. See my post on How to Make Seed Bombs at the MrBrownThumb blog for more pictures and details, and leave a comment there if you have questions. But this seed bomb making video should give you all the information you need.
Why make seed bombs? Well, it's fun. And guerrilla gardening is a great way to get kids interested in gardening, and people of all ages participating in beautifying those ugly abandoned lots that make out neighborhoods look ugly.