Why You Need to Clean Algae From Your Wood Deck (and How to Do It)

Sweeping the leaves, dirt, and debris off your wood deck can be enough to keep it relatively clean—that is, unless it’s coated in a layer of something slimy. In addition to making your deck slippery, and potentially dangerous, the growth of algae, moss, and/or fungi can do some serious damage. Here’s what to know about why your deck is so slippery, how to get rid of the slime, and why it’s so important.

Why is my deck so slippery?

Regardless of whether they’re covering grass, pavement, or a wood deck, fallen leaves make surfaces slippery when it rains. If they’re left on a deck long enough, they keep the wood perpetually moist, and create the ideal conditions for the growth of algae, fungi, or moss. Not only does a coating of algae, fungi, or moss make the deck quite slick, it may also leave green or black stains on the wood, even after the leaves and other debris have been cleared away.

Is algae bad for a deck?

Moisture is the enemy of wood. Over time, constantly damp wood may warp, swell, crack, and eventually, start to rot. When algae, fungi, and moss grow on damp wood, they tend to spread quickly, and make the moisture problem even worse—and, unlike leaves, can’t be easily swept off a deck. 

Even if, for some reason, you’re not concerned about your slippery deck being a falling hazard, and you don’t mind the green or black stains, you should still get rid of any algae, fungi, or moss covering it—it can harm your wood, and shorten your deck’s lifespan. And while algae and the like will cause more extensive damage to untreated lumber, they can grow on, stain, and harm treated wood as well. 

How do you remove algae from a wood deck?

Whether you’re dealing with algae, fungi, or moss growing on your wood deck, here are a few ways to get rid of it:

DIY bleach solution

Most advice on how to remove algae, fungi, or moss growing on your wood deck begins and ends with bleach. If you want to go straight to the hard stuff, and don’t mind working with bleach—and it running off into whatever surrounds your deck—you can make a DIY cleaning solution by mixing the following items in a large bucket:

• 1L of household bleach
• 3L of warm water
• ⅓  cup of ammonia-free powdered laundry detergent OR ammonia-free dish soap

Use the solution and a stiff-bristled brush or broom to scrub the slippery and/or stained parts of your deck, then rinse it off with a hose. Repeat the process on any stubborn spots, if needed.

White vinegar and soap solution

Combine one gallon of warm water, one cup of white distilled vinegar, and a few squirts of Dawn dishwashing liquid (or something similar) in a bucket. Once again, use a stiff-bristled brush or broom—we’re partial to the broom version, to avoid bending down and working on our hands and knees—to scrub the deck, then rinse it with a hose. Repeat if necessary. 

Use a premixed solution

There are also plenty of premixed solutions specifically formulated to remove algae, fungi, and or moss from wood decks, including 30 Seconds Outdoor Cleaner, Concrobium House & Deck Wash, and Mold Armor E-Z Deck, Fence & Patio Wash. Follow the directions on the packaging. 

Pressure washing

Though some experts caution against pressure washing a deck, others point out that it’s possible to do it without damaging the wood. The key is to use a fan attachment, and avoid high-pressure settings. If water alone isn’t cutting it, use your pressure washer to apply one of the solutions above—as long as yours is equipped with a tank or basin that allows you to do so.

Once you’ve removed the algae, fungi, or moss from your deck, do what you can to keep it clean, including sweeping any leaves and other debris off your deck right away.