Common problems we hear from customers include moss (go figure, it's wet and cool here), certainly weeds, and the lawn thinning or turning brown in summer. While I'm no fan of turfgrass, think there's far too much of it where we could instead grow much more interesting things, the homeowner who decides to grow it should pay attention to some basics on the coast to avoid these and other problems.
First, you get moss usually because there is inadequate sunlight (like under trees or beside the house) and low fertilization for the grass. When the grass thins, the moss takes advantage of the situation, being better adapted to our climate, and moves in like an unwanted relative. Sure you can use the standard moss-killer, but unless you change the conditions, it will be back.
Second, you have broadleaf weeds invading because, again, there are superior conditions for the weeds than for the grass. Low fertilization, inadequate water, compacted soil, mowing too short so that the soil is exposed to sunlight-- these are all controllable factors that create a nice home for the tougher, more drought-tolerant and less-hungry weeds.
Lawns become thin and invite weeds for all these reasons-- but chief among them on the coast is inadequate water. Believe it or not. Yes it rains like it will never stop in spring, but as soon as we get into May the rains slow down and the growth is in high gear. This puts the plants into a stress mode, and by mid-summer if they're not getting regular irrigation, the grass plants will go into dormancy-- that's what we call that nice brown color. Some of the little plants will die, and more as the ground gets hard and compacted, and more from inadequate food. Pretty soon the lawn is all patchy and half of the ground is covered with something other than grass.
Mowing height is overlooked as a cause of problems, but is key. Know what species of grass you are trying to grow and you can research the proper height and water needs. For instance, if your lawn started out as sod from the Willamette Valley, chances are it's perennial ryegrass. This type should be mowed quite long-- 2"-- for optimum growth. Perennial rye is also fairly thirsty, so it will need more water than many of the native species like bentgrass that will soon move in and take over the turf.
Consider alternatives to grass if you have a part-time home on the coast (no, I don't mean pavement)-- there are lots of great groundcovers and low-growing shrubs if you don't need wide-open playing space. If you must have a lawn, understand what kind of grass you have and what it needs, complete with a feeding and watering schedule. Letting a lawn "go dormant" may not look pretty but will save huge amounts of water and money, however you should expect that your lawn will become a mix of various plants better adapted to the site.
After all, you didn't really come to the beach to mow lawns, did you?