In most Seattle-area neighborhoods, the culprit is compacted clay soil that doesn’t drain well, combined with insufficient grading away from the house. Yards in Bellevue, Kirkland, and Redmond often sit on glacial till — a dense layer of clay and gravel left by retreating ice sheets — that acts almost like a bathtub. A French drain system, re-grading, or a dry creek bed can usually solve the problem, depending on where the water is collecting and where it needs to go.

The early signs are subtle: a slight lean (more than 1 inch per foot of height), horizontal cracks in the mortar joints, soil washing out from behind the wall, or the wall separating from adjacent structures. Timber walls in the PNW typically last 15-20 years before the wood deteriorates enough to compromise structural integrity. If your wall is leaning visibly, it’s worth getting a professional assessment before the next heavy rain season — wall failures tend to accelerate once they start.

Usually, yes — but the moss is a symptom, not the root cause. In the Pacific Northwest, moss takes over lawns that are too shady, too compacted, too acidic, or some combination of all three. A soil test (about $30 through King County Extension) will tell you your pH and nutrient levels. From there, a targeted approach — lime to correct acidity, core aeration to reduce compaction, overseeding with shade-tolerant fescue blends, and selective tree pruning to increase light — can transform a mossy lawn over one to two growing seasons.

Take it seriously. Persistent water against your foundation can lead to basement moisture, cracks, and long-term structural concerns. The fix is often simpler than homeowners expect: re-grading the soil to slope away from the house at a minimum of 6 inches over the first 10 feet, extending downspouts, and in some cases installing a curtain drain along the foundation wall. If you’re noticing dampness in your basement or crawl space, address the grading first — it’s the least expensive intervention and solves the majority of cases.

Overwatering is actually the most common cause of plant death in Seattle landscapes. Our summer dry season fools homeowners into watering on a schedule designed for much drier climates, and many PNW-adapted plants (like Oregon grape, salal, and sword fern) actually suffer from too much summer irrigation. The other common culprit is planting the wrong species for the light and soil conditions — a sun-loving plant in deep shade will decline slowly no matter how well you care for it. A quick check: if the soil an inch below the surface is still damp, hold off on watering.

Both. Moss on hardscape surfaces is a slip hazard, especially on smooth-cut stone or sealed concrete. But it can also work its way into paver joints and mortar lines, slowly prying things apart over time. Annual pressure washing (at the right PSI — too high damages pavers) and a zinc sulfate treatment keep most patios moss-free. For ongoing trouble spots, consider increasing sunlight by pruning overhead branches or switching to a textured paver surface that moss has a harder time gripping.