Lawn Care Guide for Multnomah County
Multnomah County, Oregon
USDA SSURGO / PHZMThis week in Multnomah County · next up in about 11 weeks (Oct 11)
Overseeding season is approaching.
Data Story
About Lawn Care in Multnomah County, Oregon
Balanced Growth in the Rose City
Multnomah County hits the national median with a lawn difficulty score of 50.2. This Zone 9a region offers much more favorable growing conditions than the typical Oregon county score of 38.9.
Ideal Rainfall for Healthy Turf
The county receives 49.1 inches of annual precipitation, landing perfectly within the 30-50 inch ideal range for grass. With only 14 extreme heat days, the climate is gentle on cool-season turf varieties.
Correcting Acidic Soil
Local soil is acidic with a pH of 5.35, which is lower than the ideal 6.0-7.0 range for most lawns. The 16.7% clay content means you may need to aerate regularly to prevent compaction.
Watching the Summer Dryness
Despite high rainfall, the county spent 29 weeks in drought last year and remains 99% abnormally dry. Use smart irrigation to bridge the gap during the dry July and August months.
Lush Options for Zone 9a
Perennial ryegrass and fine fescues flourish in this mild climate. For best results, start your new lawn project after the final spring frost on March 13.
Lawn Difficulty Score
Top Grass Fit for Multnomah County
Excellent match
Scotts Turf Builder Bermudagrass
Scotts
Top cultivar score: 86/100
Zone 9a vs Bermudagrass's 7–10 band.
Soil pH 5.35093362015917 vs Bermudagrass's 6–6.5 window.
Precipitation 49.122" + soil AWC vs Bermudagrass's 20–30" need.
Growing-degree-days + frost window vs a beginner-difficulty establishment.
If you live in the southern US (zones 7-10) and your lawn gets full sun, Bermudagrass is almost certainly the right choice — and Scotts is the easiest entry point.
Limited product coverage — one vetted cultivar for this species.
Shop Scotts Turf Builder BermudagrassIn Multnomah County, USDA zone 9a, soil pH 5.4, Scotts Turf Builder Bermudagrass scores 86/100 — a strong zone match, adequate moisture, and a long enough establishment window.
Why we ruled these out
- Outsidepride Midnight Kentucky Bluegrass Seed — USDA zone 9a is above Outsidepride Midnight Kentucky Bluegrass Seed's effective range (2–8); not recommended for this county.
See our fit-score methodology for how survivability is determined.
Recommended Grasses
Bermudagrass
Cynodon dactylon
St. Augustinegrass
Stenotaphrum secundatum
Choosing grass in Multnomah County
Severe drought (29 wk in drought / yr) and acidic soil (pH 5.4) are the two things working hardest against a lawn in Multnomah County. Here's how to choose for both — then the specific pick.
- Drought-tolerant grass seedWhat survives where water is scarce and often restricted.
- Amending your soil before you seedLime, timing, and the acid-tolerant shortlist.
- Bermudagrass, explainedTraits, care, and where Bermudagrass wins — the species behind your top match.
Top match for Multnomah County: Bermudagrass
See the full breakdownOften see Kentucky Bluegrass recommended? See where it fits — and why Bermudagrass takes the edge in Multnomah County’s conditions. Kentucky Bluegrass, explained
Premium Grass Seeds is a sister site in our network. We may earn a commission from qualifying purchases made through its retailer links — this never affects your price. Guidance here reflects your county’s climate and soil data, not hands-on testing.
Climate Snapshot
Annual Precip
49.1"
Growing Degree Days
2,662.04
Base 50F
Last Spring Frost
03/13
First Fall Frost
11/22
Days Above 95F
14
Hardiness Zone
9a
Seeding Calendar — Multnomah County
Personalized to this county’s frost dates — a 255-day growing season. Windows below are computed from local last-spring and first-fall frost normals, so they differ county-to-county even within USDA Zone 9A.
Plan your seeding — Multnomah County
Pick a grass and a goal to get a personalized schedule anchored to this county’s frost dates.
- 1Prepare the seedbedMar 12 – Mar 25
Mow low, dethatch or rake, and loosen the top ½ inch of soil so seed makes good contact.
- 2Sow seedMar 26 – Apr 23
Best window to sow Centipedegrass in Multnomah County, anchored to your local frost dates.
- 3EstablishApr 24 – May 21
Protect young seedlings: mow only after they reach ~3 inches and hold off on weed pre-emergents until established.
Organic (muck/peat) soil holds moisture — a single ¼-inch watering most days is usually enough; let the surface dry slightly between cycles to prevent algae and damping-off.
Seasonal Lawn Care Checklist
Spring
- Apply pre-emergent herbicide when soil reaches 55F
- Begin mowing when grass reaches 3 inches
- Start irrigation if rainfall is below 1 inch/week
- Soil test every 2-3 years — adjust lime or sulfur as needed
Summer
- Raise mowing height to reduce heat stress
- Water deeply 1-2 times per week (1 inch total)
- Avoid fertilizing cool-season grasses in peak heat
- Scout for grubs and treat if >10 per sq ft
Fall
- Overseed warm-season lawns if thinning
- Apply fall fertilizer (highest N application for cool-season)
- Continue mowing until growth stops
- Rake or mulch leaves to prevent smothering
Winter
- Apply pre-emergent for winter weeds
- Service mower and sharpen blades
- Plan spring soil amendments based on fall test
- Overseed with ryegrass for winter color
Watering Deficit Calculator
Monthly Deficit
0.0"
inches of water
Monthly Water
0
gallons
Estimated Monthly Cost
$0.00
at $0.008/gallon average
Estimates based on 49" annual precipitation and estimated evapotranspiration. Actual costs vary by local water rates.
Common Lawn Problems in Multnomah County
Acidic Soil
Soil pH of 5.4 is below the ideal range for most grasses (6.0-7.0). Apply agricultural lime to raise pH gradually.
Persistent Drought Conditions
Multnomah County experienced drought conditions for 29 of the past 52 weeks. Prioritize water-efficient grasses and consider reducing lawn area.
Learn more about regional lawn challenges at The Lawn Report.
Lawn Care Advisory: Multnomah County
Lawn Verdict
Multnomah County is in USDA hardiness zone 9a, a warm zone well-suited to heat-tolerant grasses. with winter lows reaching around 20.0°F. and 2,662.04 growing degree days, sufficient for most common turfgrasses. Moderate rainfall (49.1 inches) generally supports healthy lawns with minimal supplemental watering.
Seasonal Breakdown
Wait until after March 13 to seed or overseed; soil temperatures should consistently reach 50-55°F. Cool summers (July averages 69.2°F) reduce heat stress — maintain regular mowing and moderate watering. Aerate and overseed cool-season lawns by early fall, well before November 22; this is the best renovation window. Mild winters (January averages 41.2°F) allow year-round mowing for warm-season lawns and minimal dormancy.
Watering Guidance
With 49.1 inches of annual rainfall, established lawns typically need watering only during extended dry spells. Currently, 99.0% of the county is in abnormally dry according to the US Drought Monitor. Cool summers reduce water demand; overwatering is a bigger risk than drought stress.
Regional Context
Multnomah County is 3.9°F warmer than the Oregon average, it is significantly wetter than the state average (11.7 inches more), the growing season is noticeably longer than the state average, USDA zone 9a helps guide grass selection compared to neighboring counties.
Dig deeper into Multnomah County
Multnomah County is a USDA Zone 9A, organic-soil, warm-season county. Explore the data that shapes its lawn:
Want detailed soil composition, drainage classes, and soil series data? View soil details on SoilByCounty.com
Frequently Asked Questions
What USDA hardiness zone is Multnomah County in?
What is the best grass for Multnomah County?
How long is the growing season in Multnomah County?
How much rainfall does Multnomah County get?
What is the soil pH in Multnomah County?
Data sourced from USDA SSURGO, NOAA Climate Normals (1991-2020), USDA Plant Hardiness Zone Map, and US Drought Monitor. Lawn difficulty scores and grass recommendations are estimates for informational purposes only.
Explore more data for Multnomah County