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Why is My Cedar Deck Green and How Can I Fix it? Addressing Algae and Mold on Decking

why is my cedar deck green

A beautiful cedar deck can be the crown jewel of your outdoor living space, offering a warm, inviting area for relaxation and entertainment. However, when your once-pristine decking starts turning an unsightly and unexpected shade of green, it can be both confusing and frustrating. 

The green tint on your cedar deck is often a sign of algae or mold growth, common issues that many deck owners face. Understanding why these organisms thrive on your deck and learning how to address and prevent them are crucial steps to restoring and maintaining the natural beauty of your cedar wood. 

In this article, we'll explore the reasons behind the green discoloration and provide practical solutions to fix and prevent algae and mold on your decking. So, why is my cedar deck green, and how do I remove algae from deck boards? Let’s find out. 

Quality Cedar Products can meet all your cedar board needs. This blog is informational only and not a replacement for expert advice. Please consult a professional before starting any building project as your needs and specifications may vary and it may not reflect the most current building codes, regulations, or industry standards.

Why is My Cedar Deck Green?

First of all, why is my cedar deck green all of a sudden? What causes this color change? Let’s take a look at why green discoloration is usually a sign of algae on deck wood, and why it’s important to learn how to remove green mold from wood deck boards ASAP to extend your cedar deck lifespan

Mold, Mildew, and Algae

Mold, mildew, and algae are the primary organisms responsible for turning your cedar deck green. These microorganisms thrive in damp, shaded environments and feed on organic matter, which makes wood an ideal host. 

Algae are simple plants that form a green, slimy layer on surfaces, while mold and mildew are fungi that can appear as dark spots or patches. Both can spread quickly, especially in humid conditions, leading to widespread discoloration and potential damage to the wood.

How Did This Happen?

Why is my cedar deck green from algae and mold? Several factors contribute to the growth of mold, mildew, and algae on your cedar deck, including:

  • Moisture: Cedar decks exposed to rain, humidity, and poor drainage are prone to moisture accumulation, creating a perfect environment for these organisms.

  • Shade: Decks shaded by trees, buildings, or overhangs receive less sunlight, which would otherwise help to dry out the wood and inhibit growth.

  • Debris: Leaves, dirt, and organic debris can trap moisture and provide a food source for mold and algae.

  • Lack of Maintenance: Infrequent cleaning and sealing can allow moisture to penetrate the wood, fostering growth over time.

Keeping your deck dry and clean is key when it comes to preventing green mold on wood. 

Why Immediate Action is Important

Unfortunately, green mold on wood generally won’t go away on its own. It’s essential to act as quickly as possible, because mold, mildew, and algae can deteriorate your deck’s wood, leading to rot and structural weakness, which in turn leads to expensive replacements. 

Also, certain mold and mildew on deck boards can pose health risks, especially if anyone in your household has respiratory conditions or allergies. So, learning how to remove green mold from wood decks ASAP is important to save money, prevent damage, and keep your household safe. 

How Do You Get Green Off a Wood Deck? Tips on Cleaning Algae on Deck Boards 

So, once you identify discoloration, how do you remove algae from deck wood? Let’s take a look at some tips for cleaning your cedar decking to remove any mildew on deck boards, and what you can do to prevent mold and mildew in the future. 

Tips on Cleaning Your Cedar Decking

To clean algae off deck boards, begin by sweeping the deck to remove loose dirt, leaves, and debris, which prevents organic matter from interfering with the cleaning process. Then, use a commercial deck cleaner designed for mold and algae, or create a DIY solution with equal parts water and white vinegar.

Apply the cleaner to the deck surface and use a stiff-bristle brush to scrub the affected areas. Pay special attention to areas with heavy growth. For extensive algae growth, a pressure washer can be highly effective. Use a low to medium-pressure setting to avoid damaging the wood.

After scrubbing or pressure washing, rinse the deck thoroughly with clean water to remove any residue from the cleaning solution. Ensure the deck is completely dry before applying any protective treatments. You can also find more tips on how to clean cedar decking here!

Preventative Measures Going Forward

Learning how to remove green mold from wood decks is important, but it’s just as important to learn how to protect a cedar deck and how to care for a cedar deck to prevent mold growth. Otherwise, you may find yourself learning how to repair rot in a cedar deck and dealing with expensive replacements!

To prevent mold and mildew, keep your deck clean by sweeping regularly and washing it with a mild cleaner every few months. Ensure water does not pool on your deck by maintaining proper drainage. Check that gutters and downspouts direct water away from the deck area.

Sealing or staining a cedar deck is essential. Learn how to seal a cedar deck properly using a high-quality wood sealant or stain to protect the wood from moisture. Reapply the sealant as recommended by the manufacturer, typically every one to three years.

Trim trees and bushes around the deck to reduce shade and improve air circulation, helping the deck dry out more quickly after rain. Also, periodically move deck furniture and outdoor rugs to prevent moisture from getting trapped underneath and to allow the wood to dry evenly.

What if These Cleaning Efforts Don’t Fix the Issue?

Even if you care for your deck in all the right ways, you might still find algae on deck boards, or extensive mold damage that can’t be fixed with cleaning. In some cases (which we’ll discuss next), You may need to learn how to install cedar deck boards to replace the damaged wood. 

Signs Replacement May Be Necessary

Even if you know how to restore cedar deck boards, there are times when your deck may be past the point of saving. If the green tint remains after multiple cleaning attempts, it may have penetrated deeply into the wood fibers, making it impossible to remove completely.

Given that mold and mildew can pose a health hazard, it’s important to replace your deck boards if you’re unable to clean algae off deck wood after multiple attempts. Better safe than sorry, especially when it comes to you and your family’s health and safety. 

Also, if the boards are starting to rot, they’ll need to be replaced. Soft, spongy areas or crumbling wood indicate rot, which compromises the structural integrity of the deck and becomes a safety hazard. 

Get High-Quality Replacement Deck Boards at Quality Cedar Products!

If you do need to replace your cedar deck boards, there’s only one place to find premium cedar boards for sale. At Quality Cedar Products, our cedar decking is the highest grade you’ll find anywhere, because we personally sort and grade all our products by hand. 

As builders ourselves, we understand how essential it is to start with the best materials, and how frustrating it can be when what you receive doesn’t match the quality of what you ordered. That’s why we only deliver the best, and back it up with our 100% satisfaction guarantee. 

So, when you need to find the best cedar lumber for sale to replace those old deck boards, there’s only one place to turn - Quality Cedar Products. We’ve got the products you need at the cedar decking cost you’re looking for. 

Tips on Replacing the Green Boards

If you do need to replace your deck boards, there are a few things to keep in mind. Firstly, identify and mark all the boards that need replacement. Check for underlying structural issues that may also need addressing.

Make sure you remove the damaged boards carefully with a pry, using extra caution not to damage adjacent boards that don’t need replacing. Before installing new boards, inspect the joists and beams for signs of rot or damage. Replace any compromised elements to ensure a stable foundation.

Measure and cut the new boards to fit precisely and ensure the cedar deck board spacing is even. Use galvanized or stainless-steel screws or nails to secure the boards, preventing rust and corrosion. Learn how to sand a cedar deck to ensure a smooth surface. 

After installation, apply a high-quality sealant or stain to protect the new boards from moisture and UV damage. Ensure consistent coverage to prevent future algae and mold growth - you can find more tips on how to refinish cedar deck boards here.

Final Thoughts on How to Remove Green Mold From Wood Deck

So, why is my cedar deck green? Deck boards turning green are an indication of mold, mildew, and algae growing on your deck. Not only can this pose a risk to your health, but it can also damage your deck beyond repair if it’s not dealt with soon enough. 

Hopefully, the tips we’ve given you for preventing and treating green deck boards will help preserve your cedar deck for long years to come. But, if you do need to replace any damaged deck boards, you can find the best quality cedar here at Quality Cedar Products. 

Invest in affordable cedar that stands the test of time - shop Quality Cedar Products today. 

Quality Cedar Products does not assume any liability for the accuracy, completeness, or usefulness of the information provided in this blog post. The reader is solely responsible for any actions taken based on the information presented. Any reliance on the information is at the reader's own risk.


Quality Cedar Products is not responsible for any loss, injury, or damage that may occur as a result of following the suggestions, tips, or recommendations provided in this blog post. Building projects involve inherent risks, and it is essential to exercise caution, obtain proper permits, and engage qualified professionals to ensure safety and compliance with all applicable laws and regulations. The inclusion of external links, references, or recommendations in this blog post does not constitute endorsement or guarantee the quality, reliability, or suitability of the linked sources. The reader should independently verify the information and assess its relevance to their specific circumstances. The author reserves the right to modify, update, or remove the content of this blog post at any time without prior notice. It is recommended to check for the most recent updates or consult with professionals to ensure the information is current and applicable. By reading this blog post, the reader acknowledges and accepts the above disclaimer and agrees to use the information provided responsibly and at their own discretion.

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