REFRESHIFY

If you live in Snohomish County, you already know how quickly moss can take hold of a roof. With our long rainy season, dense tree cover, and cooler temperatures, moss thrives here more than in most parts of Washington. And while those green patches may look harmless, they can quietly shorten the life of your roof by trapping moisture, lifting shingles, and weakening the materials that protect your home.

After years of working on homes across Everett, Snohomish, Lake Stevens, Monroe, Mill Creek, and Granite Falls, I can tell you this: timing matters, and so does knowing how moss actually grows.

Summer can be a good time to remove moss, but it isn’t always the most effective season — especially in Snohomish County, where roofs heat up faster and cleaning solutions dry out quickly.

Here’s the truth as a roofing and home-improvement expert:

Why Summer Works (Sometimes)

• Dry weather gives you safe footing.
• Moss dries out and becomes easier to brush away.
• Scheduling is easier because storms are rare.

But summer has a major downside: Cleaning solutions often evaporate before they fully penetrate the moss, which means you may not get a complete kill. This can allow moss to grow back faster.

Why Moss Grows So Quickly on Shingle Roofs

Moss needs only three things to spread: moisture, shade, and organic material. Unfortunately, Snohomish County provides all three.

Asphalt shingles have a textured surface made of granules. Over time, debris like pollen, dirt, pine needles, and fallen leaves settle into those granules. That buildup becomes the perfect “soil” for moss spores, which are carried through the air year-round.

Here’s how the cycle begins:

• Moisture from our constant rainfall soaks into debris sitting on your shingles.
• Shaded areas — especially on north-facing sections of the roof — stay damp longer.
• Moss spores land on the wet surface and start spreading tiny root-like structures.
• These structures grow between shingle layers, lifting them and trapping even more water.

Once moss takes hold, it spreads slowly at first…then rapidly. That trapped moisture leads to wood rot, shingle decay, and eventual leaks — which is why early removal is so important in our climate.

When Snohomish County Homeowners Should Remove Moss

The ideal times are late spring and early fall, when the weather is mild, dry, and predictable. These seasons give you the best conditions for both safety and effectiveness.

A cloudy but dry day is perfect. Direct sun makes cleaning solutions evaporate too fast, and wet weather makes the job slippery and unsafe. Treating moss in these transitional seasons also protects your roof before summer heat or winter storms make existing damage worse.

Safe Moss Treatments for Asphalt Shingles

Most Snohomish County homes have asphalt shingle roofs, so choosing a gentle cleaning method is essential.

A traditional and reliable option is a 50/50 mix of laundry-strength chlorine bleach and water, applied with a sprayer. Let it work for 15–20 minutes and rinse it off using a low-pressure hose.

If you prefer a natural approach, mix equal parts white vinegar and warm water with a few drops of dish soap. Spray it on, allow it to loosen the moss, and rinse carefully.

Once the solution has done its job, use a soft brush or broom to sweep away remaining moss. No heavy scrubbing — gentle pressure is all you need to preserve your shingles.

Safety Tips for Snohomish Homeowners

Because our roofs hold moisture longer than other regions, surfaces stay slick well after rainfall. Always wear gloves and eye protection, use a sturdy ladder, and avoid working alone.

Never use a pressure washer. The force strips granules, weakens shingles, and can void manufacturer warranties. And always rinse thoroughly, since leftover solution can damage shingles or nearby landscaping over time.

Why Spring and Fall Are Better Overall

For Snohomish’s climate, late spring and early fall consistently deliver the best results because:

• Temperatures are mild
• Surfaces stay damp long enough for solutions to work
• Roofs aren’t dangerously hot
• Products don’t evaporate too quickly
• Rain isn’t as frequent as winter

Final Word

Moss is a part of life in Snohomish County, but it doesn’t have to shorten the life of your roof. By understanding how moss grows, removing it during the right season, and using safe application methods, you can protect your home for years to come.

If you'd rather let a professional handle the job, Refreshify Roofing provides safe moss removal, roof repairs, replacements, and flexible payment options — so you can take care of your home now and pay later.