Setting up a Ground node using SpriteKit?

I've been designing a game where I want the game to stop as soon as the ball makes contact with the ground. My function below is intended to set up the ground.

class GameScene: SKScene, SKPhysicsContactDelegate {

 var ground = SKNode() 

 let groundCategory: UInt32 = 0x1 << 0
 let ballCategory: UInt32 = 0x1 << 1

 func setUpGround() -> Void {
        self.ground.position = CGPointMake(0, self.frame.size.height)
        self.ground.physicsBody = SKPhysicsBody(rectangleOfSize: CGSizeMake(self.frame.size.width, self.frame.size.height)) //Experiment with this
        self.ground.physicsBody?.dynamic = false

        self.ground.physicsBody?.categoryBitMask = groundCategory    //Assigns the bit mask category for ground
        self.ball.physicsBody?.contactTestBitMask = ballCategory  //Assigns the contacts that we care about for the ground

        self.addChild(self.ground)
    } 
}

The problem I am noticing is that when I run the iOS Simulator, the Ground node is not being detected. What am I doing wrong in this case?

via Chebli Mohamed