when the countdown numbers turn green the mission is accomplished, if they turn red you failed. Likewise with the atombomb picture after each lvl. Green = accomplished, red = fail.
Level 19: Add the flowerseeds, put the hat on, then water it until the flowers die. Now you only have flowerseeds on the upper half of the ball. Water the flowerseeds once, then add grasseeds, and water once. =)