Every spring we get the same call: the lawn is half moss, the moss killer worked for a month, and now it's back. That's because moss doesn't take over a healthy lawn. It moves into the space grass has already given up, and grass gives up for four reasons: shade, wet soil, compacted soil, and low fertility. Fix those and the moss has nowhere to live.
Shade is the big one on the Kitsap Peninsula. Under firs and cedars, most lawn grasses simply can't get enough light. You can thin and limb up the trees to let more light through, switch to a shade-tolerant seed blend, or, honestly, stop fighting it and turn the deep-shade areas into bark beds or a moss garden.
Wet, compacted soil is the other half. Clay soil packed down by years of foot traffic and mowing holds water at the surface, which grass roots hate and moss loves. Core aeration once or twice a year opens the soil up, and topdressing with compost after aerating builds the structure back over time. Low spots that stay soggy need grading or a drain.
Once the conditions are fixed, the recovery is straightforward: dethatch to pull the dead moss out, aerate, overseed with a Northwest blend, topdress, and feed with a fall fertilizer. Do it in September or early spring when the soil is warm and the rain is doing your watering for you.
If you'd rather skip the trial and error, we do the whole sequence, from limbing the trees to laying the seed, and we can put the lawn on a maintenance schedule so it stays that way.