Deck cleaning in preparation for refinishing or sealing can be done in a morning without killing yourself.  To clean the deck, remove the dark stains without harming the wood, and guard the flowerbeds, do the following.

Before getting out the cleaner, spray the surrounding plants with lots of water to prevent them from absorbing the chemicals. Watered plants will soak up fewer chemicals than thirsty ones.

Start the cleaning with Wolman's DeckBrite or oxygen bleach. The black spots that the Wolman's or oxygen bleach does not get up can be removed with wood bleach (oxalic acid).

Mix the deck cleaner according to the directions and apply it to the deck with a scrub brush on a broom handle. This will keep you on your feet and allow you to cover a larger area quicker, not to mention saving your back and knees.

Wolman's DeckBrite and oxygen bleach foam as they clean the deck like using hydrogen peroxide on a cut. Let the product work for 10 to 15 minutes and then apply a light second coat and scrub lightly.

For dark stains that oxygen bleach cleaners do not get out, switch to oxalic acid (wood bleach). Mix a saturated solution, very strong, in warm water and apply twice within five minutes. If it does not lighten the stain, use a wire brush and moderately scrub with the grain of the wood. This will open the pores in the wood and allow the wood bleach to work. Keep the area coated with the wood bleach while you are scrubbing. The stain should disappear before your eyes.
 
If you feel you have to use a power washer on a deck, be careful not to ruin the wood by blowing off all the soft pulpwood. When using a power washer, be sure to use it on low power, use a wide spray tip, and keep the nozzle 24" from the wood.

If the deck looks good when it is wet, it should look good with a stain on it.
The important thing to remember is to be sure the deck is dry before sealing. Do not apply a deck stain to damp wood! Sealing in moisture is guaranteed to ruin most deck finishes.

We use KUSHGUARD DECK STAIN or Valspar's Wood Toner to protect our decks. They have penetrating oils and a UV protector. The oils penetrate deep into wood fibers displacing water, preventing rot and splitting.