A lawn composed of a mix of locally adapted grass species growing in well-drained, fertile soil on a site with adequate sun will have few disease or pest problems, and can out-compete most weeds with proper management.
The first step in maintaining a healthy lawn is to avoid practices that diminish the natural vigor of the turf ecosystem, such as broadcast applications of pesticides (which kill beneficial soil organisms as well as target species), over-watering (which promotes shallow rooting and fungal diseases), over-fertilization (which promotes thatch buildup, decreases soil bio-diversity, and forces lawns to grow too fast), and improper mowing (mowing at the wrong height or too infrequently).
Kentucky bluegrass does not grow well west of the Cascades, although up to 10% in a mix can perform the same function as rye of closing the canopy quickly, before it dies out.
Tall fescues need to be mowed higher, 3" - 4" and have a rougher appearance. But they develop deep root systems in good soils and stand up to drought, poor drainage, and salty soils better than most grasses. And they have the fescues? low fertilizer requirements. They are bunch-type grasses, and don?t spread into garden beds like creeping varieties.
Colonial and creeping bentgrass do spread, but are well adapted to western Washington. Colonial bentgrass look best when mowed at 1" (or even less, down to 1/2") though this also means a shallow root system and quick browning in the summer.
?Low Grow? mixes that are slower growing (and don?t require fertilization after they?re established) generally include the slow-growing Barclay?s Rye along with fescues and white clover. They can be mowed and watered less frequently.
Washington Lawn diseases: Red thread is the only real problem here on naturally managed turf. It is temporary, and does little damage.
Washington Insect Problems: European crane fly larvae that eat grass roots in late winter are the only real problem in western Washington. Water infrequently in late summer and make sure that the upper 2" of soil dries out completely between watering's; or stop irrigation altogether, especially if crane fly adults are seen on the lawn.
Unlike most plants, grasses have leaves that grow from a crown near the soil surface rather than from their tips. This allows some grass plants to go dormant during the dry season and recover without damage when fall rains come. (Turf-type ryegrasses do not go fully dormant, and are susceptible to drought damage; fescues, on the other hand, are much more resistant to drought damage.)
So one approach to lawn irrigation is to just forget it, and let the lawn go brown. But in Washington's long, dry summers growing crowns may be damaged, especially in ryegrass, and the lawn is placed at a competitive disadvantage to deep-rooted weeds like dandelions.
Many turf professionals recommend that dormant lawns be watered deeply once each rainless month, but because the soil is very dry, though, the water penetrates more slowly. To avoid wasting water in run-off, use the start and stop method or a very slow sprinkler. Again, water deeply: check to see that the soil is moistened as deep as the roots reach.
CAUTION: Dormant lawns do not stand up to wear very well, so areas that are used for play or other heavy traffic should probably be irrigated regularly to avoid damage. Continue to mow dormant lawns often enough to keep dandelion flowers from setting seed, and bag clippings if many seed heads are present.
Professional lawn care associations: Northwest Turfgrass Association, Western Washington Golf Course Superintendents Association