American Grass

Northwestern States

Includes: Washington, Oregon, Montana, Idaho, and Alaska

Planning the Pacific Northwest lawn

When choosing which grass species to plant, consider how you’ll use the lawn. You’ll need a more rugged variety of grass to stand up to ball games and picnics than if you’re only planting a lawn just for looks.

Take a look at the shape of the area where you want to establish the lawn. Especially in the rainy Northwest, lawns should have a slight slope away from buildings or sidewalks to let excess water run off. A slope of anywhere from 1% to 6% is ideal.

If you’re planting in a hilly Seattle neighborhood, though, keep in mind that while a slope of up to 12% is acceptable, any steeper and you’ll have problems with mowing and watering. For steep slopes, you can either re grade or opt for a hardy native ground cover like slender wintergreen (Gaultheria ovatifolia) or inside-out flower (Vancouveria hexandra) instead of lawn grass.

While the lawn area might slope, the surface itself should be even. If there are low spots where rainwater could puddle, even them out before you plant.

Soil types west of the Cascades

The black clay found in Oregon impedes drainage, but by working compost into the soil can take care of this problem. If you’re higher up in the Cascades, you may be dealing with decomposed granite, in which case you’ll have to add a considerable amount of organic material like topsoil and compost before much of anything will grow.

Partly due to heavy rainfall leaching the soil, high pH (acidic) soils are common in the Pacific Northwest. To find out if you’ll need to amend to soil to lower the pH or add minerals such as calcium, magnesium, potassium or phosphorus, have a soil test done by a local nursery or conduct one yourself using one of the kits available at gardening centers.

Types of grass for the Pacific Northwest

The Pacific Northwest/Cascade region mostly falls into USDA climate zones 8 and 9, with zone 7 starting in the Cascade foothills and zone 6 occurring higher up. The turfgrass map also used by some landscapers places the Pacific Northwest in the cool/humid zone. For these zones, the best choices are:

  • Fine fescues like red fescue

  • Certain bluegrasses and ryegrasses

  • Bentgrasses also grow well in the Northwest, but they require plenty of sun and regular maintenance.

  • Dwarf tall fescues near the coast. Theses will need to be allowed to grow higher, but they offer a deep green color and tolerate salt better than most species.

  • Buffalo grasses

  • Zoysia grasses can also be grown in the Northwest, but they do better in the warm climates of southern Oregon and northern California

  • Bermuda grass is another possible choice for warm microclimates areas

As a rule, for sports, choose rye; if it’s just for show, go with fescue. Fescues do well in sun, but still keep a healthy green color in the shady areas. Most ryegrasses need full sun to thrive, but they stand up to foot traffic better than fescues.

In most cases, the ideal will be fine fescues such as creeping red or chewings mixed with ryegrass. The rye is useful because it sprouts quickly and offers coverage to prevent weed growth.

The grasses that do grow well, such as the turf-type fescues and perennial ryegrasses, have a lighter, meadow green color when grown on fertile soils (though some newer cultivars are darker than others).

Don’t forget about native grasses, either. Because natives are adapted to local conditions, when planted in an appropriate site, they don’t need nearly as much watering or fertilizing as imports.

Grasses native to the western Cascade region include Oregon bentgrass (Agrostis oregonesis), western fescue (Festuca occidentalis) and creeping red fescue (Festuca rubra), blue wild rye (Elymus glaucus), Alaska onion grass (Melica subulata), and Columbia sedge (Carex aperta).

One grass to avoid in the Pacific Northwest is Kentucky bluegrass (Poa pratensis). Although popular in the north, most areas of the Northwest are too wet for this prairie grass. It does sprout quickly, though, so having a small amount in the seed mix will provide temporary coverage before the rest of the grass comes in.

Building soil health

The starting point for building soil and grass health is knowing what’s there. A soil analysis is an excellent beginning, whether you’re installing a new lawn or improving an old one.

The test can reveal acid conditions, which are common west of the Cascades because of rainfall leaching the soil or because of previous use of synthetic fertilizers, and the results will also tell how much lime to add to correct this condition.

Salt build-up from soluble fertilizers or nutrient deficiencies of calcium, magnesium, sulfur, phosphorus, and potassium are all difficult to determine visually, but easy to read from the test results, which should include recommendations about how much of what amendment is needed to correct the problem.

The following are recommend practices that support the natural vigor of grass plants and the soil community that sustains them, and minimize the need for practices that diminish that vigor.

  • Setting realistic expectations for lawn appearance, and tolerating a few weeds.

  • Proper site selection and preparation of the soil by tilling in compost to a depth of 6" - 12"

  • The selection of site-adapted and disease-resistant grasses.

  • Moderate fertilization with natural or natural/synthetic-slow-release combination fertilizers, to build soil nutrient reserves and bio diversity.

  • Mulch-mowing (also called “grasscycling”) whenever possible.

  • Mowing regularly (remove only 1/3 of grass height each time), and mowing a little higher, at 2" - 2-1/2" on most lawns (or 1" for colonial bentgrass lawns)

  • Avoiding over-watering: watering deeply, to moisten the whole root zone, but infrequently, to limit disease and build deeper roots; and watering dormant lawns at least once a month during the dry season, to improve post-drought recovery.

  • Renovation/improvement practices that include aeration, compost topdressing,and overseeding, to reduce compaction, increase water infiltration, improve soil structure and natural disease control, and crowd out weeds.

Lawn problems associated with soil problems

Problems to look for include:

  • Overall yellowish, thin lawn appearance, with weeds getting the upper hand: unhealthy, infertile soil, correctable with the practices outlined in Renovating Old Lawns.

  • Yellow or brown patches in grass: signs of dog urine damage, fertilizer burn, scalping with lawnmower, or sometimes disease or insect damage. Water and time will cure the first three of these.

  • Heavy clay soil, or hardpan a few inches down, causes poor drainage and root development – in extreme cases lawn may need to be torn out and compost tilled in 8" deep to improve the soil structure, before replanting. Compost incorporation is the key to both “opening up” clay soils and to improving the fertility and moisture-holding capacity of sandy soils.

  • Hard, compacted soil are signs of heavy wear, usually correctable over time with core aeration, grasscycling, compost topdressing, and then avoiding use of chemicals toxic to earthworms.

  • Compacted soils may also be found after years of heavy pesticide and soluble fertilizer use.

  • Infertile soil with little organic matter: usually lighter in color, sandy, gravelly, sometimes subsoil left after grading for construction. Again, compost is the answer.

  • Poor drainage: standing water in winter; blue, gray, yellow or black soils, sometimes bad-smelling. Area may need to be re-graded so water drains off, or soil may need to be improved with compost so water drains through, or both, followed by replanting. Sometimes a subsurface drainage system can be installed to drain the root zone, but this is expensive and will require maintenance. In extreme cases, consider replacing the lawn with ground cover plants that tolerate saturated soils.

  • Shallow root development: all of the above conditions can cause this, as well as inadequate topsoil depth, frequent shallow or excessive watering, and excess thatch layer. Roots should extend at least four to 6" into soil, be white or light tan color and be strong enough to be hard to pull out.

  • No worms: usually caused by overuse of pesticides and soluble fertilizers, sometimes by very poorly drained soils. Soil life will return over 1 - 2 years with proper management. Worms working the soil aerate, improve drainage, and incorporate thatch, grass clippings, and top dressed compost into the root zone— they are the best, easiest, cheapest lawn improvement tool you can get.

  • Root-eating grubs: crane fly larvae are the only serious insect problem in this region, sometimes causing noticeable brown patches in early spring, but birds feeding on the lawn in the winter usually keep them under control. If you see more than 25, ¾" long gray-brown grubs per square foot when you turn back the lawn “rug” in February or March, turn to the Crane Fly section.

  • Excess thatch: the layer of tough, brown, fibrous material on top of the soil in your plugs is called thatch. It is roots, stems, and stolons (above-ground roots) that haven’t broken down yet (not grass clippings). 1/2" of thatch helps turf stand up to wear; more than that is a problem causing shallow root development and poor water infiltration. It’s usually a sign of over-fertilization, over-watering, compacted soil, or over-use of chemicals, particularly on thatch-prone bentgrass lawns. See Thatch Removal.

  • Moss: may be a sign of acidic, compacted, infertile, over-watered or poorly drained soil, or a site that’s just too shady for grass. Essentially the moss is out-competing the grass for space. To help the grass re-colonize the site, correct the problem conditions.