Conditions, history, and source details
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Planning the year
See Harlan scheduleFertilizer
A foliar iron spray darkens the lawn's color without forcing the leaf growth a nitrogen feeding would, which is exactly what summer-stressed turf needs. Iron is taken up directly through the leaves, so results show in days rather than weeks. Shallow soil temperatures are in the action band at 75°F at 2 inches at the Shagbark Hills sensor, 59 miles from your location.
Source: Shagbark Hills station
Pest Watch
White grubs are the larvae of Japanese beetles, June bugs, and similar species, and they feed on grass roots through summer. Catching the first generation in early summer, before significant root damage, makes preventive insecticide much more effective than rescue treatments. Shallow soil temperatures are in the action band at 75°F at 2 inches at the Shagbark Hills sensor, 59 miles from your location.
Source: Shagbark Hills station
Lawn Care
Fall aeration after a hot summer relieves compacted soil and gives roots access to air, water, and nutrients heading into the cool-season recovery window. Pairing aeration with overseeding drops the new seed into open holes for ideal soil contact. Shallow soil temperatures are in the action band at 75°F at 2 inches at the Shagbark Hills sensor, 59 miles from your location.
Source: Shagbark Hills station
Depth: 2" • Last 12 Months
Shagbark Hills (Site 2068), IA
USDA NWCC AWDB soil temperature observations.
| Date | 2" °F | Δ 2" | 4" °F | 8" °F | 20" °F | 40" °F |
|---|---|---|---|---|---|---|
| Aug 17 | 74.8 | 0.0 | 75.9 | 75.7 | 73.0 | 69.1 |
| Aug 16 | 74.8 | -0.6 | 75.7 | 76.1 | 73.4 | 69.1 |
| Aug 15 | 75.4 | +0.6 | 76.3 | 76.5 | 73.6 | 69.1 |
| Aug 14 | 74.8 | -1.7 | 75.9 | 76.3 | 73.9 | 68.9 |
| Aug 13 | 76.5 | -1.0 | 77.7 | 77.5 | 74.1 | 68.7 |
| Aug 12 | 77.5 | 0.0 | 79.2 | 78.3 | 73.8 | 68.5 |
| Aug 11 | 77.5 | — | 79.3 | 77.5 | 73.0 | 68.5 |
Soil temperature by depth
Zone 5B
October 9
1,400 ft
Cool-season core
Ideal conditions for cool-season grass. As of August 19, the 2-inch soil temperature is tracking the 10-year normal for this date. The fall seeding window is open now. Cool-season seed should establish reliably at current soil temperatures. With an average first frost of October 9 and an elevation of 1,400 feet, your fall seeding window timing is shaped by both soil temperature trends and frost risk. Zone 5b winters mean the soil freezes hard enough that early-spring readings lag the air by several weeks. Data comes from the USDA station at Shagbark Hills, 59 mi away.
For established lawns and gardens, the 4 inch soil temperature is a more useful reading than the surface. This 4-inch root-zone depth changes more slowly than the 2-inch surface layer, so it is a steadier signal for timing fertilizer, aeration, and weed control. The depths your nearest station reports are shown above; stations in the federal network typically report 2, 4, 8, 20, and 40 inches, while modeled estimates for areas far from a station cover fewer depths.
This week’s watering for Harlan, IA
Ease off: about 0.85 inches tops off what the rain will leave short
| Weekly target | 1.13 in | at 75°F soil, for cool-season grass |
|---|---|---|
| Expected rain | 0.3 in | over the next 7 days |
| You supply | 0.85 in | in 2 deep sessions, watered 4-9 AM |
The weekly target includes rainfall, so irrigation only covers the deficit. Water deeply and infrequently rather than a little every day: shallow daily watering builds shallow roots and invites disease. Rainfall is a modeled forecast estimate for this location.
How to water by soil temperature, and audit your sprinklers →
Soil moisture near Harlan, IA
Wetter than normal
The 2-inch soil is at 36% volumetric water content, around the 77th percentile of this station’s own history for this time of year.
Measured at 2 inches by a USDA SCAN station, as of August 17.
The wetter-or-drier comparison uses this station’s own readings within about two weeks of today’s date, pooled across 5 years (135 readings). Frozen-soil days are left out. Baseline last computed July 19.
Lawn disease risk
The 7-day forecast near Harlan, IA favors active disease pressure. These diseases are the ones to watch now. Based on a modeled weather estimate for this location.
| Disease | Risk | Why now |
|---|---|---|
| Dollar spot (Clarireedia jacksonii) | Favorable | 7 of the next 7 days sit in its 60-85°F window; worse on underfed turf. Keep adequate nitrogen and remove morning dew (early mowing or dragging a hose) to shorten the wetness window. |
| Rust (Puccinia spp.) | Favorable | 7 of the next 7 days sit in its 65-85°F window; worse on underfed turf. Feed adequately and irrigate early so foliage dries fast; adequate nitrogen lets turf outgrow rust's slow cycle. |
How temperature drives lawn disease, and the cultural fixes →
Growing degree days near Harlan, IA
Michigan State ground-truthed these models in the Great Lakes region and does not recommend them for the mid-south transition zone or the South. Outside the Upper Midwest and Northeast, read them as a guide and confirm against local extension guidance.
Growing degree days measure the heat a lawn has accumulated this year: each day adds the amount its average temperature runs above 50°F, the point where cool-season growth and most pests get going. Turf managers use the running total to time crabgrass pre-emergent, annual bluegrass seedhead suppression, and grub control. Pairing it with the current soil temperature shows both the season's heat so far and what the ground is doing right now. Measured at the NOAA station Lincoln 8 ENE.
Soil temperature readings on this page cover 2 ZIP codes in Harlan, IA:
51537, 51593
Know when to seed, fertilize, and stop crabgrass at your address. The timing here comes from live in-ground readings at your nearest USDA or NOAA monitoring station, not from the calendar.
Check the current soil temp at your location, or open the live US soil temperature mapto see today’s ground readings from 380+ USDA and NOAA stations across the country. Enter your city or ZIP code for live soil temperatures near you, plus planting windows, pre-emergent timing, fertilizer guidance, and disease watch alerts based on your nearest USDA monitoring station.
Readings refresh nightly from the USDA-NRCS Soil Climate Analysis Network and the NOAA US Climate Reference Network (USCRN). Readings are measured by in-ground sensors at federal monitoring stations, not estimated from weather models; see how we measure. Planting windows are derived from multi-year climatology, overlaid with NOAA 1991–2020 frost normals where a station is close enough to support a local frost date. 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.
Browse soil temperature data by state, over 2,000 cities with current readings, hardiness zones, and planting windows.
Explore the US Soil Temperature Map for a live station view of readings across the country.
Current soil temperature: 75°F at the 2-inch depth, 0.2°F above the historical average for this date. Measured August 17, 2026 at the Shagbark Hills USDA station, 59 miles away. Falling 2.7°F over the last 7 days.
Current conditions in Harlan, IA
75°F
2-inch depth
A foliar iron spray darkens the lawn's color without forcing the leaf growth a nitrogen feeding would, which is exactly what summer-stressed turf needs. Iron is taken up directly through the leaves, so results show in days rather than weeks. Shallow soil temperatures are in the action band at 75°F at 2 inches at the Shagbark Hills sensor, 59 miles from your location.
View detailsExpected rain covers part of the weekly target. Irrigation only needs to make up the remaining deficit.
View details7 of the next 7 days sit in its 60-85°F window. This is a conditions indicator, not a diagnosis or prediction.
View detailsAir and rain
Weather context
Right now the ground near Harlan is wetter than usual for this time of year: the soil at 2 inches holds 36% water, around the 77th percentile of this station's own history for the date. The reading is measured at the station, not modeled.
For warm-season grasses, yes. The 2-inch soil temperature near Harlan, IA is currently 74.8°F, measured in the ground at the Shagbark Hills monitoring station (59.4 mi away). That is at or above the 65°F threshold where Bermuda and zoysia establish, and above the 50–65°F cool-season band, so hold cool-season seeding until soil cools back through 65°F.
The soil at 2 inches near Harlan, IA is at 36% volumetric water content, around the 77th percentile of this station's own history for this time of year, so the ground is wetter than usual for this date. This is a direct ground measurement from 337 active USDA and NOAA in-ground monitoring stations, not a forecast or a model.
Soil temperature outside the germination band is the most common cause. The 2-inch soil temperature near Harlan, IA is currently 74.8°F, measured in the ground at the Shagbark Hills monitoring station (59.4 mi away). Cool-season seed germinates at 50–65°F and warm-season seed at 65°F or higher; outside those bands seed sits dormant rather than sprouting. If the temperature is right, the usual culprits are seed buried too deep, topsoil that dried out during the sprout window, or a pre-emergent herbicide applied the same season, which blocks grass seed the same way it blocks weeds.
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°F or higher before seeding. If you are seeding, a high-phosphorus starter fertilizer goes down in the same window; regular established-lawn fertilizer follows different timing.
Apply pre-emergent herbicide, the product sold at retail as crabgrass preventer, 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, and applying after that point reduces effectiveness significantly. Weed-and-feed products that include a pre-emergent follow the same window. The pre-emergent timing page for Harlan tracks this threshold against the current reading.
Harlan, IA is in USDA hardiness zone 5b. Cool-season grasses (tall fescue, Kentucky bluegrass, perennial ryegrass) are built for winters here and stay alive under frost and snow. Warm-season grasses risk winterkill in this zone: Bermuda and zoysia come through mild winters but thin or die back in hard ones.
Use 2 inches for germination decisions, since that is where seeds sit. Use the 4 inch soil temperature for established lawn and garden timing: it reads the root zone, changes more slowly than the surface, and is the depth most fertilizer, aeration, and disease guidance references. The 8 inch reading shows deeper root-zone trend. The 20 and 40 inch readings track deep soil and frost depth where federal stations report them.
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.
It is a direct ground measurement. The 2-inch soil temperature near Harlan, IA is currently 74.8°F, measured in the ground at the Shagbark Hills monitoring station (59.4 mi away). Soil Temps reads from 337 active USDA and NOAA in-ground monitoring stations, which report daily at depths from 2 to 40 inches.
Each window above is counted on its own base temperature and start date, which is why those numbers differ from the headline total. A target range means nothing without them.
Grass seed germination
Your soil near Harlan, IA: 75°F at 2 inches, as of August 17, 2026.
| Grass species | Seeding soil temp (2 in) | Days | Right now |
|---|---|---|---|
| Kentucky bluegrass | 60–70°F | 14-30 | Too warm to establish |
| Tall fescue | 60–70°F | 7-12 | Too warm to establish |
| Perennial ryegrass | 60–70°F | 5-10 | Too warm to establish |
| Fine fescue | 60–70°F | 7-14 | Too warm to establish |
| Bermudagrass | 75–90°F | 10-30 | Germinates slowly |