Lawn Care Guide for Multnomah County
Multnomah County, Oregon
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
Recommended Grasses
Bermudagrass
Cynodon dactylon
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 — Zone 9A
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.
Want detailed soil composition, drainage classes, and soil series data? View soil details on SoilByCounty.com
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.
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