To keep your deck and wood healthy, beautiful and long lasting it is important to keep it protected from the sun.  In addition to protecting your wood from the damages of the sun, it also must be kept clean –much like skin must be kept clean to stay healthy.  It is healthier for wood to be thoroughly cleaned and stained every 2 and 4 years than to extend it out every 6 to 7 years.  Dirt falls down, accumulates and gets ground into the horizontals surfaces of your wood.  This dirt needs to be removed with a thorough cleaning every couple years.  The vertical portions of your deck will not accumulate dirt like the horizontal surfaces so the vertical surfaces need to be thoroughly cleaned and stained only every 4 years.  Using a deck stain that is not found in stores and is used for commercial use, is the best decision for maintaining your wood.