Dry the siding first if you notice signs of mold growth.
How to bleach out cedar siding.
One method used to determine if spots are from these two conditions is to treat them with a solution of bleach 1 part diluted with water 9 parts.
It is non toxic to trees and vegetation and will not remove natural color from the siding.
How to clean cedar siding with bleach 1.
The safe and effective way to clean the wood is oxygen bleach.
Look for a powdered oxygen bleach that does not contain sodium hydroxide or potassium hydroxide as these could damage the wood s protective finish.
Mix the oxygen bleach in a ratio of 2 cups of powdered granules to 1 gallon of water or based on the product and manufacturer s instructions on the label pour the mixture into a cleaned out lawn and garden sprayer.
Cover about a 4 by 8 foot section with the liquid and let it sit on the siding for about 15 minutes.
Dip a sponge in the vinegar solution and wipe it on the bleached wood.
Rinse the sponge in clear water before dipping it again in the neutralizing solution.
Once the cedar is dry you can leave it as is or apply the finish of your choice.
But if you want to lighten it again in the future i d leave the cedar natural.
You can dry wood siding using a dehumidifier or a space.
Removing the the wood mold with oxygen bleach.
Water any grass.
Put on a pair of heavy duty rubber gloves because you are about to deal with bleach which can prove highly irritable.