Linda in Oakville has finished a deck and asks Jon about the correct stain to use.
Stains are optional and only serve the purpose of changing the colour of the wood. Opaque stains are not made for walking surfaces, they are not durable enough.
What is not optional is a water repellent and some form of rot protection. Cedar and Redwood both have good natural rot protection. Brush, spray or dip preservative treatments for white woods are not going to last very long because they are just on the surface, so when we use construction white woods we always use pressure treated lumber. That makes it about the most durable outdoor wood available.
But all wood left to the elements will begin to check and develop cracks and splinters. This is independent of any of the rot protection. Checking is controlled by preventing water from getting into the wood, with water repellents. Some pressure treated wood also has a built in water repellent. All other deck wood must have a water repellent, with or without stain, applied the first season. Water repellents have to be renewed whenever you find that a glass of water poured on a dry deck no longer beads up, but rather flows into the wood.