Permission is required except for dropping objects that are considered ballast, such as water, sand or fuel. For objects that do not pose a risk of injury, such as petals, small flyers, etc., a take-off permit is usually issued. You can apply for a take-off permit from the relevant state aviation authority (LuftVO § 13.1). The transport of hazardous materials such as pyrotechnics is generally prohibited.
Drones are already being used to drop parasitic wasps to control pests such as the European corn borer, but also to take samples from the air or water for closer examination of their components.