"I've been following guerrilla gardening on Twitter for quite some time, and have become familiar with the term 'seed bombing' as a result. It's an idea that's always appealed to me – it's a kind of eco–friendly, bee–friendly, slightly radical anti–vandalism activism – but it's just one of those things that I'd never pursued. ...
So how do they work? It's a simple process really – the seeds I bought are encased in a ball of peat–free compost, dried clay and chilli, which are hand–rolled in North London (yes, really, and no, it's not what you're thinking). The dried clay acts as a protective casing from common seed predators (such as ants, mice and birds). When enough rain permeates the clay, the seeds inside begin to germinate – helped along by the nutrients and minerals contained within the balls. So it's like a tiny self–sufficient seeding system. Maya [http://www.mayaproject.org/] have added chili powder to the mix to help to deter predators while the seed ball slowly degrades, and eventually the seeds sprout."
(Lucy Small, 5 April 2013)
http://www.seedball.co.uk/content/about
http://www.mayaproject.org/
http://twitter.com/guerillagarden