You should re-stain your deck before the weather gets too hot and your wood too dry! The best way to accomplish this is by wetting down your deck and scrubbing it with a biodegradable wood cleaner and a stiff-bristel brush. This will remove all of the dirt and grime, and prepare the wood for staining. Rinse this, and allow the deck to thoroughly dry before applying your stain. There are lots of stain colors and styles available on the market, so be sure to speak with a professional about which is best for you and your space!
