The term "seed grenade" was first used by Liz Christy in 1973 when she started the "Green Guerrillas". The first seed grenades were made from condoms filled with local wildflower seeds, water and fertilizer. They were tossed over fences onto empty lots in New York City in order to make the neighborhoods look better. It was the start of the guerrilla gardening movement...Seedbombs by Greenaid
The earliest records of aerial reforestation date back from 1930. In this period, planes were used to distribute seeds over certain inaccessible mountains in Honolulu after forest fires. Seed bombing is also widely used in Africa; where they are put in barren or simply grassy areas. With technology expanding, it is now placed in a biodegradable container and "bombed" grenade-style onto the land. As the sprout grows, the container biodegrades and the plant grows. It is usually done as a large-scale project with hundreds dropped in a single area at any one time. Therefore, a barren land can be turned into a garden in a little over a month.
Seed bombing (Wikipedia)
"How to Make a Seed Bomb" (Instructables)