Portland
Treat broadleaf46°F↑ warming
Fall is the best time to treat dandelions and clover: they pull weed killer down to their roots.
Broadleaf window Sep 11 – Nov 8
Oregon Weed Watch · updated Nov 3, 1:18 AM CT
When to apply pre-emergent in Oregon
Live soil temperatures for Portland, Eugene, Medford and Bend, updated every three hours. Weeds sprout by soil temperature, not by the calendar, so the right week moves from year to year.
In Oregon, pre-emergent is a spring job: it stops crabgrass. Fall is seeding season here, so fall weed control means treating broadleaf weeds instead.
Spring pre-emergentNext season
Typically Mar 22 – May 15
Stops crabgrass and other summer weeds before they sprout.
Fall: no pre-emergentThis season
Treat broadleaf weeds Sep 1 – Nov 9
Fall is seeding season here, and pre-emergent would stop grass seed too.
Right now · fall (seeding season)
Treat broadleaf weeds now: Portland and Eugene. Broadleaf season over: Medford and Bend
Soil is 38–46°F now. In fall, dandelions, clover and creeping Charlie pull sugars — and weed killer — down to their roots. Seeding this fall? Skip pre-emergent; it stops grass seed too.
Soil temperature by city
Soil 2 inches down, 5-day average: solid line = the last two weeks, dashed = the six-day forecast.
Eugene
Treat broadleaf46°F↑ warming
Fall is the best time to treat dandelions and clover: they pull weed killer down to their roots.
Broadleaf window Sep 1 – Oct 26
Medford
Done for now44°F↑ warming
Done for this year. Spot-treat on a mild day, or wait for spring.
Broadleaf window Sep 11 – Nov 9
Bend
Done for now38°F↑ warming
Done for this year. Spot-treat on a mild day, or wait for spring.
Broadleaf window Sep 1 – Oct 15
Oregon pre-emergent calendar
Spring pre-emergent stops crabgrass. The window runs from the typical day soil warms to 50°F to the day it holds 55°F, when crabgrass starts germinating (2016–2025). In fall Oregon lawns are in seeding season, so there is no fall pre-emergent; the window shown is for treating broadleaf weeds instead, from September until two weeks after soil usually cools to 55°F.
| City | Spring pre-emergent (crabgrass) | Fall (seeding season) |
|---|---|---|
| Portland | Mar 22 – Apr 27 | None (seeding season) · treat broadleaf Sep 11 – Nov 8 |
| Eugene | Apr 17 – May 15 | None (seeding season) · treat broadleaf Sep 1 – Oct 26 |
| Medford | Mar 27 – May 5 | None (seeding season) · treat broadleaf Sep 11 – Nov 9 |
| Bend | Apr 22 – May 5 | None (seeding season) · treat broadleaf Sep 1 – Oct 15 |
These are typical-year dates (the median of 2016–2025); any one year can run a couple of weeks earlier or later, which is what the live readings above are for. For your exact yard, check soil temperature by ZIP.
What people in Oregon are identifying
We record the state each identification comes from. Oregon's list appears here once it has at least 40 identifications spread over 7 or more days — so no single scan stands out. Until then, see the national list, or add yours:
Identify a weed from a photoWeeds to watch in Oregon this fall
Questions about Oregon
When should I apply crabgrass pre-emergent in Oregon?
Put crabgrass pre-emergent down as soil warms to 50°F, before it holds 55°F and crabgrass starts germinating. In a typical year (2016–2025) that window is Mar 22 – Apr 27 in Portland; Apr 17 – May 15 in Eugene; Mar 27 – May 5 in Medford; Apr 22 – May 5 in Bend.
Should I put down pre-emergent in the fall in Oregon?
Usually not. Fall is the best time to seed a cool-season lawn in Oregon, and pre-emergent stops grass seed as well as weeds. Fall is the time to treat broadleaf weeds such as dandelion, clover and creeping Charlie, once the summer heat breaks and while they are still growing.
What is the soil temperature in Oregon right now?
As of Nov 3, 1:18 AM CT: Portland 46°F, Eugene 46°F, Medford 44°F, Bend 38°F (5-day average, about 2.4 inches down). Treat broadleaf weeds now: Portland and Eugene. Broadleaf season over: Medford and Bend.
How the readings and dates are made, and their limits: Weed Watch method. Soil data: Open-Meteo.com (CC BY 4.0); typical dates: NASA POWER.