I recently heard about seed balls (small balls of clay, soil and seeds mostly used to add plants to abandoned areas) and while I very much like the idea I was a little bit skeptical of their effectiveness.
Could anyone with experience describe how effective they are, and how to maximize their effectiveness?
The only related question I could find on SE was this one, which highlights a few important parameters to keep in mind (humidity and integrity of the ball) but doesn't say anything about the success rate of well designed balls and doesn't give a particular recipe: How to properly seed bomb a particular area with drones
While I would really like learning about general guidelines, if such general recommendations are impossible to give, I am more specifically interested in the effective design of seed bombs for urban areas of western Europe, hardiness zone 6, with seeds that promote future growth (seeds that can survive and maybe help with soil compaction as well as poor soil quality).