Why does my fence have green or black streaks?

A board-on-board cedar fence creates a private seating area

Does your fence have streaks of black or even green? Whether it’s vinyl or wood this means mold or mildew is making a home—and if you live in wet climates like what we have in the greater Portland area, your fence is even more vulnerable.

You’ll be happy to know this issue can be prevented and removed with a little love.

Vinyl Fence

If you see mildew growing on your vinyl fence, it’s important to address it sooner rather than later. The black or green color of the growing mold can dig into the fence, and may cause a permanent discoloration; this is especially true for a white vinyl fence. Vinyl fence posts are particularly prone to mold as they are frequently in contact with wet soil.

How to prevent it

Stains can be prevented by regular cleaning. How often to do it depends on location, for example if the fence is in a shaded area it’s more likely to develop green streaks and patches. Also, make sure to keep trees and bushes away! Trim plants to be a minimum of 1 foot from the point of contact—that includes leaves.

How to get rid of it

If mildew has already begun to grow, and it hasn’t been sitting there for years, you can clean it with a soft cloth or brush. Use either soapy water or a vinyl cleaning solution. Just be careful not to scrub so hard that scratches appear on the fence panels! Here’s an easy DIY vinyl cleaning solution recipe:

  • ½ cup white vinegar (red doesn’t make much sense…)
  • 1 gallon of water
  • 1 rag or spray bottle
  • A little elbow grease
  • Some time

If you use a rag, just wipe it down Miagi style. If you use a spray bottle, aim straight and douse it!

For more detailed steps, check out our guide to cleaning a white vinyl fence.

Wood Fence

Similar to vinyl fences, mold and mildew can really dig into wood fences. Thankfully, they too can be both protected and restored.

How to prevent it

Staining a cedar fence will go a long way to protecting it from mold and mildew. However, whether you do or don’t stain the wood, it’s still a good idea keep it clean by using 3 parts water and 1 part bleach. Spray it down, then spray it down again with regular water. Easy as that.

In addition to regular fence cleaning, make sure to keep plants 1 foot away from being in contact with any part of the fence. Standard cedar posts are vulnerable at their base, however another option is to use galvanized steel posts for wood fences. Here’s a little more info: Why Choose Metal Posts

How to get rid of it

We recommend a mixture that’s a bit stronger. Add 2 parts warm water to 1 part bleach, then drop in about a ¼ cup of dish washing soap per 2 quarts of solution. Same as before, spray thoroughly, then rinse with a garden hose.

But what if that still doesn’t work?

Well then it may be caused tannins, and now it’s time to up the ante. Bust out some oxalic acid with warm water and go to town. There are also plenty of professional cleaning solutions out there if that’s a little to DIY for you. For more details, read our guide to removing moss and mildew from your cedar fence.

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