Helps tailor timing recommendations to your grass type
Recommendations
Weed Prevention
NOT YET
It is still a little early for spring pre-emergent timing
Shallow soil temperatures are still below the typical action band. Keep monitoring conditions before acting.
ℹ️
When to come back
The weed prevention window typically opens when the 3-day soil temperature average reaches 50°F to 55°F. Current 3-day average is 44.7°F — bookmark this page and check back in a week.
NOAA USCRN soil temperature dataConfidence: Medium
Details: methodology, thresholds, and confidence
Methodology
Method: Based on historical soil temperature patterns and climatology rules
Depth: 4-inch soil temperature (primary evaluation depth)
Conditions
Temperature range: Window opens when 4-inch soil temps sustain above 50°F and closes above 65°F
Stability requirement: Requires 7 consecutive days of sustained temperatures
Frost adjustment: Window end date adjusted based on average first frost date (Oct 22, 356, ~733 km) with a 42-day safety buffer
Confidence
Confidence: Medium confidence because historical patterns at this location show some variability.
Source: NOAA USCRN soil temperature data.
Fall window: Aug 1 – Sep 10
Average first frost: Oct 22 (356, ~733 km). Fall recommendations stop 42 days earlier.
Daily Soil Temperature
Depth: 2" • Last 12 Months
Showing chart
Nearest USDA Station
Boulder 14 W (Site USCRN-94075) — CO
Distance: 33 miles from Denver, CO
Elevation: 5330 ft
Coordinates: 40.0400, -105.5400
NOAA USCRN soil temperature observations.
The 2-inch reading first crossed 50°F on May 23 — the pre-emergent window opened that day.
Date
2" °F
Δ 2"
4" °F
Apr 22
46.4
↑ +1.4
44.8
Apr 21
45.0
↑ +2.4
43.3
Apr 20
42.6
↑ +2.0
41.4
Apr 19
40.6
↑ +4.3
39.4
Apr 18
36.3
↑ +0.5
36.7
Apr 17
35.8
↓ -5.6
37.0
Apr 16
41.4
—
40.6
Find the current soil temperature in your area and make confident lawn timing decisions. Enter your ZIP code for ground temperature readings near you — plus planting windows, pre-emergent timing, fertilizer guidance, and disease watch alerts based on your nearest USDA monitoring station.
How Soil Temperature Drives Lawn Timing
Track how soil temperatures are trending at your location with daily readings and 12-month historical data. Unlike air temperature forecasts, soil temps change gradually — a sustained warming trend over several days is a stronger planting signal than any single reading. Enter your ZIP code above to see the current soil temperature trend and forecast for your area.
Soil temperatures — sometimes called ground temperatures — shift more slowly than air readings, making them a more reliable indicator of root zone conditions. When the 2-inch depth reaches germination thresholds for several consecutive days, weed seeds activate — that is your signal for pre-emergent timing. At 4-inch depth, sustained temperatures above 65°F indicate warm-season grass is actively growing and ready for fertilizer or aeration. Compare the planting window and recommendation guidance above with the daily chart below to make your decision.
About the Data
Readings refresh nightly from the USDA-NRCS Soil Climate Analysis Network and the NOAA US Climate Reference Network (USCRN). Planting windows are derived from multi-year climatology overlaid with NOAA 1991–2020 frost normals. Recommendation cards evaluate current soil conditions against research-backed thresholds from university extension sources. Check back regularly as conditions change — the guidance updates with every new reading.
Data sources: USDA-NRCS SCAN network, NOAA USCRN, NOAA 1991–2020 climate normals, and localized frost climatology via Soil Temps analytics.
Ideal conditions for cool-season grass. As of April 24, the 2-inch soil temperature is running 10°F above the 10-year normal for this date. The spring seeding window opens around June 5, roughly 42 days out. With an average first frost of October 22 and an elevation of 5,330 feet, your fall seeding window timing is shaped by both soil temperature trends and frost risk. Zone 6a sits in the tall-fescue transition belt where both cool- and warm-season grasses have to be timed carefully. Readings come from the Boulder 14 W USCRN research-grade station, 33 mi away.
What soil temperature is needed to plant grass seed?
Cool-season grasses like fescue and bluegrass germinate best when soil at 2 inches stays between 50–65°F for several consecutive days. Warm-season grasses like Bermuda and Zoysia need soil temperatures of 65–70°F or higher before seeding.
How deep should I measure soil temperature?
Measure at 2 inches for germination decisions — that is where seeds sit. For established lawn health, 4-inch readings indicate root-zone conditions and help time fertilizer, aeration, and disease prevention.
What’s the difference between soil temperature and air temperature?
Soil changes temperature much more slowly than air due to thermal mass. A warm afternoon does not mean the ground is warm. Soil temperature lags air temperature by days or weeks, making it a more reliable indicator of when biological processes like germination actually begin.
When should I apply pre-emergent based on soil temperature?
Apply pre-emergent herbicide when soil at 2 inches reaches 55°F for several consecutive days. This is the threshold where crabgrass and other summer annual weeds begin germinating. Applying after this point reduces effectiveness significantly.
What is a USDA Plant Hardiness Zone?
USDA Plant Hardiness Zones divide the US into 13 zones based on average annual extreme minimum temperature. They help determine which plants and grasses can survive winter in your area. Zone numbers increase from coldest (1a) to warmest (13b).
