All these projectiles are delayed action bombs. When you attack in the fall the flowerbombs will explode during spring. Attacking in spring or summer the bombs will explode after a few weeks. Nevertheless; the earlier your attack (best in march/ april) all the stronger the expliosion gets.
In the folowing movie you will see the use of the flowerbomb. Try to bomb fast and unnoticed. Be sure of your target. Think of places that are easy to remember so you can see if your flowers are growing. Remember that the road to succes is to keep on flowerbombing the city and having patience.