Growth on cedar siding

Asked July 14, 2016, 11:53 AM EDT

Hello! We are getting ready to stain our cedar siding house and need answers as to how to remove a growth we've found on the wood. First time we've seen this growth in 20 years of owning the house. Tried killing it with a bleach water solution, but didn't seem to affect it. Thanks for your assistance. Anita

Polk County Oregon

1 Response

Well, I must say I'm surprised that bleach didn't work. The two primary discoloration agents on wood are iron (which results in black stain, commonly around fasteners) and fungi. Oxalic acid (wood bleach) is recommended for iron stain. However, what you have here looks more like either fungi or perhaps even lichen. Household bleach should take care of fungi. From what I've read about lichen, it's recommended to scrape or pressure wash. If you opt to pressure wash, go gently because cedar is pretty soft and damages quite easily (voice of experience...).

If you need a more definitive ID, you might try removing a sample and bringing it to your local Master Gardeners.