4 Types of Grass in Oregon and Which Side of the Cascades Wants Each

Ask an Oregon State University turf specialist what grass to plant and the first question back is which side of the Cascades you live on. That single ridge line splits Oregon into two lawn climates that barely overlap. The west gets cool, wet winters, which is why OSU says western Oregon residents "will likely prefer perennial ryegrass," and why Kentucky bluegrass, "susceptible to cool-weather pathogens" there, will not persist as a major part of the lawn. The east gets real winters, snow cover, sandy soil, and summers where OSU's own calendar says an unirrigated lawn "will not survive more than one year," which flips the recommendation to Kentucky bluegrass. Add the coast and the Rogue Valley as their own wrinkles, and you have a state where the right bag of seed depends on your address more than almost anywhere else. Here is the OSU-backed lineup, how to identify what is already in your yard, and the planting calendar for both Oregons.

The types of grass that grow in Oregon

Perennial Ryegrass

West of the Cascades, perennial ryegrass is the lawn. OSU's irrigation guide for Oregon turf puts it plainly: "Residents of Western Oregon, where winter weather is cool and wet, will likely prefer perennial ryegrass." It sprouts in about a week, which is the main reason it anchors the west-side mix. In OSU's retail seed trial in Corvallis, uncoated mixes of 58 to 68 percent perennial ryegrass with fine fescue "produced the most attractive stands," so a ryegrass-led mix with fine fescue is the label to look for. The catches: it wants full sun and regular nitrogen, it thins out in shade, and it goes straw brown without summer water. It is a bunchgrass, so bare spots need seed rather than filling in on their own. East of the mountains OSU is blunter, warning that "Perennial ryegrass may be injured in Central/Eastern Oregon because of its poor cold tolerance," so over there it is a mix partner, not the base.

Fine Fescue

Fine fescue is the quiet half of the standard western Oregon mix, and in shade it becomes the whole lawn. OSU's Practical Lawn Care for Western Oregon notes that "fine fescue is adapted to partial shade and drought conditions," and the OSU irrigation guide adds that it "is well-adapted to low fertility and shady environments" and "capable of persisting with little or no irrigation." Three types show up on Oregon seed labels: creeping red, Chewings, and hard fescue. OSU notes that with the exception of hard fescue, perennial ryegrasses and most fine fescues are susceptible to red thread, which it calls "the number one complaint about this mixture" of ryegrass and fine fescue; it looks bad but does not kill the grass. Under trees, OSU suggests roughly 70 percent fine fescue with 30 percent ryegrass, mowed at about 2 inches. One honest twist: if you want it green through July rather than merely alive, fine fescue needs more frequent summer watering than ryegrass, so decide up front whether you are buying a low-water lawn or a low-input one.

Tall Fescue

Tall fescue is the grass OSU sends to Oregon's hot spots. Practical Lawn Establishment and Renovation calls it "a good choice for hot areas such as LaGrande and Medford" and "adapted to much of central and eastern Oregon," and adds that with deep watering "you should be able to wait 5 to 10 days between irrigations." OSU's irrigation research backs that with numbers: tall fescue needs 26 to 43 percent of evapotranspiration replaced to look good, against 32 to 49 percent for ryegrass, the lowest of the lawn grasses tested. The coarse blade is the giveaway, and it is why OSU says it "performs best in pure stands" rather than in a mix. Plant it alone at 8 to 12 pounds per 1,000 square feet, mow it around 3 inches to push deeper rooting, and fix bare spots with seed, because it bunches rather than spreads. One caution for the wet side of the state: in western Oregon it "tends to go semidormant in the winter" and is prone to leaf spot and Microdochium patch, especially its first winter.

Kentucky Bluegrass

Kentucky bluegrass is the east-side grass. OSU's retail seed bulletin says it "is the most common lawn grass east of the Cascades, but disease susceptibility makes it poorly suited to locations west of the Cascades," and the OSU irrigation guide names it "the best turfgrass species" for high-quality lawns in Central and Eastern Oregon. The reasons are cold and recovery: OSU calls it cold tolerant, says it goes dormant during periods of snow cover, and notes it recovers in spring with "an aggressive, rhizomatous growth habit" that lets the lawn recover well from foot traffic. The bill comes as inputs. It can take three weeks or more to germinate, wants frequent mowing, fertilization, and irrigation to look its best, and east of the Cascades OSU says irrigation is required for any turf to persist. OSU's east-side recipe is simple: a mixture of Kentucky bluegrass and perennial ryegrass. In the Willamette Valley it "will not persist as a major component of the lawn," so leave it out of west-side bags unless you are prepared to lime and fight disease for it.

Two grasses that nobody plants deserve a mention, because in western Oregon they end up in your lawn regardless. OSU's western Oregon lawn guide is candid that after establishment, well-fed and well-watered lawns "often transition to stands dominated by annual bluegrass and rough bluegrass," while low-input lawns "will likely be populated by bentgrasses." Annual bluegrass (Poa annua) reads lighter green with heavy seedheads in spring; bentgrass forms a fine, matted patch that OSU's mowing table puts at a 1-inch cut. Neither is a disaster. OSU even suggests that west of the Cascades a mix with a quarter colonial bentgrass "probably is the mix that most homeowners should plant," since it invades anyway and you may as well have a uniform lawn from the start. One more label warning from OSU: skip anything with annual ryegrass, which it files under "junk grass included in cheap seed mixes."