What to do in O'Fallon now
O'Fallon is in cool-season grass country. Dates are typical for this spot, worked out from 23 years of weather at St Louis Spirit Of St Louis Ap; each status uses this year's soil estimates.
Cool-season: tall fescue, Kentucky bluegrass, perennial ryegrass, fine fescue
- Crabgrass pre-emergent Closed Mar 25 Typical: Mar 19 – Apr 62-inch soil held 55°F for a week from Mar 25, so crabgrass was sprouting. Next window: about Mar 19 – Apr 6, 2027.
- Seed or overseed Seed now · last days Typical: Sep 22 – Oct 30The window usually closes by Oct 30, but this fall has kept 4-inch soil at 65°. Seed only if you can keep it moist, and expect slower germination as soil cools.
- Late-fall feeding Final feeding from about Nov 7 Typical: Nov 7 – Dec 4Not too late. Feed on your normal fall schedule; the last feeding of the year goes down when 4-inch soil falls to about 50°F (typically Nov 7) and before it reaches 40°F (typically Dec 4).
Warm-season: bermudagrass, zoysia, St. Augustine, centipede, bahia
- Crabgrass pre-emergent Closed Mar 25 Typical: Mar 19 – Apr 62-inch soil held 55°F for a week from Mar 25, so crabgrass was sprouting. Next window: about Mar 19 – Apr 6, 2027.
- Seed or sod Wait for late spring Typical: May 8 – Sep 22Warm-season seed needs 4-inch soil at 65°F or more, and seedlings need the rest of summer to establish. Next window opens about May 8.
- Fall pre-emergent (Poa annua) Germinating since Sep 29 Typical: By Sep 214-inch soil fell below 70°F on Sep 29, when annual bluegrass begins to sprout. A pre-emergent now only stops later flushes; plan to apply by about Sep 21 next year.
- Dormancy and last feeding Any day now Typical: Around Oct 30Warm-season grass slows and browns once 4-inch soil stays under 55°F, typically Oct 30. Make the last nitrogen feeding at least a month before that.
The last 60 days and the week ahead
O'Fallon soil is 13° warmer than normal for Nov 3, warmer than on 97% of those dates since 2005, and 17° warmer than a year ago.
The green line is our estimate of the daily average soil temperature 2 inches down, driven by temperatures at St Louis Spirit Of St Louis Ap, 15.2 km from the city center. The dashed part runs the National Weather Service forecast through the same model. Hover or tap for any day.
2-inch soil, estimated From the NWS forecast Normal Normal range (8 years in 10)
Show the numbers
| Date | 2-inch soil | 4-inch soil | Air high / low | Normal (2 in) |
|---|---|---|---|---|
| Oct 21 | 57° | 60° | 76° / 41° | 56° |
| Oct 22 | 58° | 60° | 77° / 42° | 56° |
| Oct 23 | 58° | 60° | 76° / 42° | 56° |
| Oct 24 | 59° | 60° | 76° / 43° | 56° |
| Oct 25 | 59° | 61° | 79° / 44° | 55° |
| Oct 26 | 60° | 61° | 77° / 47° | 54° |
| Oct 27 | 60° | 61° | 71° / 46° | 54° |
| Oct 28 | 60° | 61° | 79° / 45° | 53° |
| Oct 29 | 62° | 63° | 82° / 51° | 52° |
| Oct 30 | 63° | 64° | 76° / 54° | 51° |
| Oct 31 | 63° | 64° | 68° / 56° | 51° |
| Nov 1 | 62° | 63° | 64° / 59° | 51° |
| Nov 2 | 63° | 64° | 70° / 58° | 51° |
| Nov 3 | 64° | 65° | 70° / 63° | 51° |
| Nov 4 (forecast) | 60° | 62° | 59° / 43° | 51° |
| Nov 5 (forecast) | 58° | 60° | 63° / 44° | 51° |
| Nov 6 (forecast) | 54° | 57° | 56° / 35° | 51° |
| Nov 7 (forecast) | 51° | 54° | 54° / 34° | 51° |
| Nov 8 (forecast) | 50° | 53° | 61° / 35° | 51° |
| Nov 9 (forecast) | 51° | 53° | 65° / 40° | 50° |
| Nov 10 (forecast) | 52° | 54° | 68° / 42° | 49° |
Which grass grows in O'Fallon
O'Fallon winters are cold enough (January averages 32°F) that cool-season grasses, mostly Kentucky bluegrass, tall fescue and perennial ryegrass, make up most lawns. They grow in spring and fall and slow down in summer heat.
O'Fallon soil through the year
Weekly 2-inch estimates for 2026 so far against 2025 and the normal for each week. The red lines mark 50°F, when crabgrass pre-emergent should be down, and 65°F, when warm-season seed sprouts well.
2026 2025 Normal (2005–2025) 8 years in 10
Normal by month
| Month | 2 in | 4 in | Air |
|---|---|---|---|
| Jan | 35° | 37° | 32° |
| Feb | 37° | 38° | 36° |
| Mar | 46° | 47° | 46° |
| Apr | 56° | 57° | 56° |
| May | 66° | 67° | 66° |
| Jun | 77° | 78° | 75° |
| Jul | 80° | 82° | 79° |
| Aug | 79° | 80° | 77° |
| Sep | 72° | 73° | 69° |
| Oct | 59° | 61° | 57° |
| Nov | 46° | 48° | 45° |
| Dec | 38° | 39° | 36° |
Soil: average of our daily estimates, 2005–2025. Air: NOAA 1991–2020 normals for the station.
Typical lawn dates in O'Fallon
Each date is when the soil estimate (or the air, for freezes) crossed the threshold, year by year since 2005. “Early” and “late” are the 10th and 90th percentile years, so 8 years in 10 fall between them.
| Event | Typical | 2026 |
|---|---|---|
| Last spring freeze (32°F) | Apr 13 | Mar 28 |
| Crabgrass model: 250 growing degree days | Feb 20 | Feb 17 |
| Pre-emergent window opens (2-inch soil 50°F) | Mar 19 | Mar 9 |
| Crabgrass begins to sprout (2-inch soil 55°F) | Apr 6 | Mar 25 |
| Cool-season lawns start growing (4-inch soil 55°F) | Apr 7 | Mar 15 |
| Warm-season seeding opens (4-inch soil 65°F) | May 8 | Apr 15 |
| Cool-season seeding opens (4-inch soil under 70°F) | Sep 22 | Oct 5 |
| Cool-season seeding ends (4-inch soil under 55°F) | Oct 30 | not yet |
| Warm-season grass goes dormant (4-inch under 55°F) | Oct 30 | not yet |
| First fall freeze (32°F) | Oct 28 | not yet |
| Roots stop feeding (4-inch soil under 40°F) (in 19 of 21 years) | Dec 4 | not yet |
Checked against a real sensor
Measured nearby: 65°F at 2 inches on Nov 3, at the USDA SCAN site “Shaw Nature Reserve”, 22 miles away.
Our estimate for O'Fallon on Nov 3 is 64°F; the sensor read 65°F at 4 inches against our 65°F. Sensor sites sit in open, unwatered ground outside town, so they often run a few degrees apart from city lawns; use them as a check on the trend.
There is no soil sensor in most cities, so we estimate it. Shallow soil follows air temperature with a lag of a few days, and runs a little warmer than the air in fall. We fitted that relationship to 190 USDA soil-sensor stations; on years held out of the fit, the estimate was off by 3.3°F on an average day, and it put the spring 55°F date within a median of 3 days. Read the methodology.
Weather: RCC ACIS station KSUS (ST LOUIS SPIRIT OF ST LOUIS AP), daily data since 1987. Forecast: National Weather Service, LSX office, issued Nov 4, 2026, 5:51 AM EST. Last observed day: Nov 3, 2026.
O'Fallon questions
What is the soil temperature in O'Fallon today? Our estimate for Nov 3 is 64°F at 2 inches and 65°F at 4 inches, as a daily average. Early-morning soil runs a few degrees cooler than that, and afternoon soil warmer.
When should I put down crabgrass pre-emergent in O'Fallon? Apply when 2-inch soil holds about 50°F and before it holds 55°F. That has typically been Mar 19 to Apr 6 in O'Fallon. For 2026 the window closed on Mar 25.
Is it too late to overseed in O'Fallon? Seed now · last days. The window usually closes by Oct 30, but this fall has kept 4-inch soil at 65°. Seed only if you can keep it moist, and expect slower germination as soil cools.
Is it too late to fertilize in O'Fallon? Final feeding from about Nov 7. Not too late. Feed on your normal fall schedule; the last feeding of the year goes down when 4-inch soil falls to about 50°F (typically Nov 7) and before it reaches 40°F (typically Dec 4).
When is the last frost in O'Fallon? The last 32°F night of spring has typically come around Apr 13, and as late as Apr 23 in 1 year in 10. The first fall freeze typically arrives around Oct 28.
Why 2 inches and 4 inches? Crabgrass and most weed seeds sprout in the top inch or two, so pre-emergent timing follows 2-inch soil. Grass seed and roots respond to the slightly steadier soil at about 4 inches.
How accurate is this? It is a model, not a probe in your yard. Expect about 3–4°F of difference on a given day; shade, slope, mulch and irrigation all move real soil. The dates and trends are more reliable than any single day.