Conditional — Some Areas
Congo signal grass (zones 10-13) reaches only part of Oregon (5a-10a): zone 10 are in range, so where you are in the state decides it.
One zone short — what would close it
Congo Signal Grass is hardy to zone 10, and the warmest ground in Oregon is zone 9 — 1 zone short. Planted in open ground it will not survive a Oregon winter. To grow it here, grow congo signal grass in a container and move it under cover for the coldest weeks, or give it a greenhouse.
Season extension and overwintering under cover both work at this margin. How to buy the weeks →
Zone math from 10-13 (plant) against 5-9 (Oregon). Lift modeled by crop_engine Sprint 20B effective_zone_modifier (+2 zones) via api/fast_sections.py Unlock Engine v2.
Your yard isn't the whole zone.
Oregon spans zones 5a-10a, but your yard has its own microclimate — slope, trees, and low spots shift frost and sun across a single parcel. Enter your address and we'll score congo signal grass against your land's actual soil, sun, and frost.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
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Zone Comparison
Congo Signal Grass Needs
- USDA Zones: 10-13
- Frost-Free Days: 120+
- Sun: Full Sun
Oregon Has
- USDA Zones: 5a-10a
- Last Hard Freeze (28°F): Feb 25 - Apr 26
- First Hard Freeze (28°F): Oct 19 - Nov 26
- Annual Rainfall: 8-90 inches
- Common Soils: Volcanic, Silt loam (Willamette), Sandy loam
Plant Zone Range (zones 10-13)
Preferred Soil pH
Plant data: USDA PLANTS Database / Growable Ground plant catalog. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant Congo Signal Grass in Oregon
The frost window
Across Oregon, the last spring hard freeze (28°F) clears between Feb 25 and Apr 26, and the first fall hard freeze lands between Oct 19 and Nov 26 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 176-day window you can count on — up to 274 days on a mild site in a kind year. That marks the hard freeze, not the last light frost, so tender transplants usually wait another 2-3 weeks.
Frost tenderness
Congo Signal Grass is frost-tender — its listed minimum temperature is 66.2°F (USDA PLANTS Database) — so set plants out two to three weeks PAST your local last hard freeze, not on it and not on the state's earliest date. The 28°F marker above is when killing freezes stop, not when light frost does.
When to start the seed
Congo Signal Grass is direct-sown where it grows rather than started under cover, so there is no seed-tray head start to bank — Oregon's dates above are the whole calendar for it. That makes the last-freeze date the binding constraint, and a warmer pocket of your own yard is worth more to this crop than it is to a transplanted one.
Timing tuned to sub-state frost dates — Klamath County, not the statewide average.
Frost window: NOAA Climate Normals 1991-2020. Plant timing fields: USDA PLANTS Database. Your site's own frost dates can run earlier or later than the state range — a parcel report pins them down.
Growing Season Fit
The zone check says congo signal grass survives winter in part of Oregon, not across all of it. Whether the season is long enough — and warm enough — is a different question.
Frost-free days
Congo Signal Grass wants 120+ frost-free days; a typical Oregon site sees ~213 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves comfortable headroom for succession planting.
GDD and chill-hour figures are computed from PRISM 1991-2020 monthly climate normals; frost-free days from NOAA Regional Climate Centers ACIS, 1991-2020. Each is the state median across its counties (P25/P75 span the within-state spread). Hardiness-zone range is USDA PHZM 2023.
Soil + Drainage Fit
Congo Signal Grass tolerates a wide pH range (pH 4.5-7.5) — 3 units, acid ground through alkaline — so soil acidity is rarely what limits it in Oregon. A soil test is still worth having, but for what else it tells you about this site, not to clear this plant. It will grow across that whole span, but it does best between pH 5.5 and 6.5 — worth knowing before you decide whether a Oregon soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your Oregon site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
Your land, not the state average
Oregon's soils run mostly silt loam, but SSURGO maps the series, texture, and drainage under your exact parcel. Congo Signal Grass needs about 19 inches of workable depth, so it is that horizon — not the surface — you are testing for. That map unit, not the state average, decides how congo signal grass performs.
Check your parcel → Source: USDA NRCS SSURGO.
Plant pH and drainage requirements from USDA PLANTS Database. Oregon soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Congo Signal Grass in Oregon — Quick Answer
- Verdict: Conditional — Some Areas
- Plant Zones: 10-13 (USDA PLANTS Database)
- State Zones: 5a-10a (USDA ARS PHZM 2023)
- Growing Season: 28°F hard freezes about Feb 25 - Apr 26 to Oct 19 - Nov 26 (NOAA Regional Climate Centers ACIS, 1991-2020)
What Else to Consider for Congo Signal Grass in Oregon
Zone compatibility tells you about winter cold survival — but Oregon growers also need to think about:
West side: excessive rain and overcast skies reduce sun for warm-season crops
East side: arid conditions (8-15 inches rainfall) require irrigation
Slug pressure is extreme in western Oregon
Mountain areas have very short seasons (60-90 frost-free days)
Growing congo signal grass here specifically
Oregon's soils run mostly silt loam (Mollisols), and whether that suits congo signal grass's pH 4.5–7.5 preference comes down to your exact parcel, not the statewide picture.
Pull your parcel's SSURGO map unit, test pH, and amend toward congo signal grass's 4.5–7.5 target before planting. How to handle it →
What to actually do about these — and the constraints that apply to every Oregon grower, not just congo signal grass — is covered on the Oregon growing guide.
Timing shifts within Oregon
Oregon isn't one climate. In Klamath County, the last hard freeze (28°F) holds until about Jun 9 — roughly 67 days later than the recorded state median — so plant congo signal grass to your county's window, not the statewide date.
Congo Signal Grass needs about 120 days of frost-free season to complete its cycle. 35 of Oregon’s 36 counties give it that outright. The tightest that does is Lake County at 134 frost-free days — 14 to spare. Below that line you are transplanting or extending the season, not direct-sowing.
Across Oregon’s 36 counties the frost-free season runs from 86 days in Klamath County to 308 days in Lincoln County — a spread of 222 days, which is why a single statewide planting date misleads. The median Oregon county sees 213 frost-free days, leaving congo signal grass about 93 days of slack on a typical parcel — room for a second sowing where the season runs long.
County last-freeze dates and frost-free day counts: NOAA Regional Climate Centers ACIS (1991-2020), county 28°F freeze (earlier than the folk 32°F "last frost"). Congo Signal Grass's 120-day requirement: USDA PLANTS / Growable Ground plant database (minimum frost-free days). A parcel report resolves your address's own frost dates.
Oregon Cooperative Extension
For Oregon-specific cultivar recommendations, planting calendars, and pest pressure for congo signal grass, the canonical source is OSU Extension Service. Their fact sheets carry the local trial data we can't generalize across 50 states.
Common Questions About Growing Congo Signal Grass in Oregon
When can I plant Congo Signal Grass in Oregon?
Oregon's last spring hard freeze (28°F) clears between Feb 25 and Apr 26, and the first fall hard freeze lands between Oct 19 and Nov 26 (NOAA Regional Climate Centers ACIS, 1991-2020). Congo Signal Grass is frost-tender — its listed minimum temperature is 66.2°F (USDA PLANTS Database) — so wait two to three weeks past your site's last hard freeze, when light frost has also stopped, before planting out.
What hardiness zone is Congo Signal Grass grown in across Oregon?
Oregon spans USDA hardiness zones 5a-10a (USDA ARS PHZM 2023). Congo Signal Grass carries a range of zones 10-13, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical Oregon site have?
A typical Oregon site sees ~213 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Congo Signal Grass needs 120+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date. In cooler counties like Klamath, the freeze-free season runs shorter than the state average, so verify your own county's window.
How should I amend the soil for Congo Signal Grass in Oregon?
Congo Signal Grass tolerates pH 4.5-7.5 and well (dry spells) drainage (FAO ECOCROP). That is a 3-unit span, acid ground through alkaline, so pH is rarely what limits this plant on a Oregon site — amend for drainage and organic matter first.
Will Congo Signal Grass actually grow on my specific land in Oregon?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores congo signal grass against your address's exact soil pH, drainage, sun, and frost-date data drawn from USDA SSURGO, NOAA, and PRISM — not state averages.
Check your specific parcel in Oregon
State-level data is a sketch. Your Growable Ground report scores congo signal grass against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Oregon congo signal grass averages can't show:
We read public map data around Oregon — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Oregon congo signal grass average
Explore More
Growing guides for congo signal grass
Analysis by the Growable Ground research team, grounded in USDA PLANTS, USDA NRCS SSURGO, NOAA Climate Normals (1991-2020), and named Cooperative Extension sources. How we know →
Cite this dataset
Kirchick, M. (2026). Growable Ground Plant Database [Data set]. Zenodo. https://doi.org/10.5281/zenodo.21435643
Licensed CC BY-NC 4.0. DOI 10.5281/zenodo.21435643
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