Nothing may be more natural than plain old water. By blasting the algae with pressurized water, you will remove it from concrete without chemicals. Wear a pair of safety goggles to prevent possible damage to your eyes from the pressurized water. Attach your water hose to the pressure washer and switch the washer on. Push the algae off the concrete with the pressure washer. Move the washer in a steady, horizontal motion while moving upwards. Continue in this manner until you have removed all traces of the algae.
A common ingredient in many all-natural cleaning recipes, vinegar will kill algae, moss, mold and mildew from various surfaces including vinyl siding and concrete. Fill a bucket with equal parts water and white vinegar and mix with a spoon. Dip a brush broom in the mixture and begin scrubbing the algae off the vinyl siding or concrete. Scrub in a back-and-forth motion -- while saturating the broom in the mixture when needed -- until you have removed all traces of the algae. Rinse the vinegar mixture off the surface with a water hose.
The soap you use to keep your dishes sparkling clean will remove the algae without harsh chemicals. Fill a bucket with warm water. Pour 1/4 cup of dish soap that does not contain bleach in the water and mix with a long-handled spoon. Dampen a brush broom in the mixture and begin scrubbing the algae off the vinyl siding or concrete. Alternatively, use a scrub brush if a brush broom is not available. Once the algae is no longer present, rinse the surface clean with a water hose.
Found in the laundry aisle of most department stores, oxygen bleach works in the same manner as chlorine bleach without the destructive and toxic chemicals. Since oxygen bleach is in a powdered form, you must dissolve it with water. Use 1 cup of oxygen bleach for every gallon of water. Scrub the algae off the surface with the mixture and let sit for 10 minutes before rinsing the siding or concrete with a water hose.