Answer: Moss is quite common in regions with damp summers like the Pacific Northwest and is generally symptomatic of several underlying conditions, including poor fertility, compacted soils, too much shade, poor drainage, and low pH. Correcting these problems will usually stop moss from growing. Since you've just seeded your lawn, you shouldn't have to worry too much about moss developing in the first year or two. You should have your soil tested before adding lime; soil test result will list the soil pH, and if it's too low, recommend the amount of lime needed.
Keep your lawn healthy maintaining proper nutrient levels, watering when rainfall is sparse, and mowing regularly to keep it at the right height. Thick, healthy turfgrass will crowd out any moss that tries to grow -- except for areas in deep shade where grass will struggle. There, consider planting other shade-tolerant ground covers.
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