About This Site

What we track

Lawn jobs like pre-emergent herbicide, grub control, overseeding, and aeration only work inside narrow windows driven by soil conditions, not by the date on the calendar. We track Growing Degree Days (GDD, base 50°F, accumulated from January 1) and an estimated 2–4 inch soil temperature for every US ZIP code, and translate them into a plain answer: too early, getting close, apply now, or window closing.

• Pre-emergent herbicide timing — apply-now window at 150–200 GDD, before crabgrass germinates
• Grub Control timing — preventive window at roughly 1,000–1,300 GDD, before beetle eggs hatch
• Overseeding timing — cool-season seeding window while soil holds 50–65°F
• Aeration timing — spring and fall active-growth windows keyed to soil temperature
• Soil temperature map — estimated soil temperature by state and ZIP, updated daily
• Live preventive grub-control report — a daily national summary with reusable data and graphics

Data sources

Every number on this site is computed from public, primary-source data:

• NOAA GHCN-Daily — daily maximum and minimum temperature observations from thousands of US weather stations.
• US Census ZCTA Gazetteer — the latitude and longitude of every US ZIP Code Tabulation Area.

We don't interpolate from national gridded models or forecasts — each ZIP code's numbers come from actual thermometer readings at nearby stations.

Methodology

1. Station matching. Each of the 33,000 ZIP codes is mapped to its eight nearest NOAA stations by Haversine (great-circle) distance. Using eight stations gives a fallback chain when a station reports late or has gaps.
2. Daily GDD. For each day since January 1 we compute max(0, (Tmax + Tmin) / 2 − 50°F) and add it to the running total. This is the standard averaging method used by university extension programs.
3. Estimated soil temperature. We estimate 2–4 inch soil temperature by relaxing the previous day's estimate toward each day's mean air temperature (an exponentially weighted average with a ~4-day time constant, floored at 32°F for frozen ground) — a simplified form of the published Zheng–Hunt–Running daily soil temperature model. Turf-covered soil at that depth lags air temperature by roughly 3–5 days, which is exactly what this smoothing captures. Expect about ±5°F versus an in-ground thermometer, with the largest errors under persistent snow cover.
4. Status thresholds. The signals are compared against operational timing bands for each job: 150–200 GDD for spring pre-emergent, the site's broad 1,000–1,300 GDD phenology band for preventive grub planning, 50–65°F soil for cool-season seeding, and active-growth soil ranges for aeration. These are planning cues, not pesticide-label instructions or universal biological cutoffs.

The bands are informed by published university extension guidance, but GDD totals are only comparable when the calculation method, base temperature, and start date match. They mark broad biological windows, not precise dates — local microclimate, shade, species, and soil moisture can shift local timing. Always follow the current product label.

Update frequency

The data pipeline downloads fresh NOAA observations and recomputes GDD for every ZIP code daily. Station observations typically lag 2–5 days behind real time; the freshness of your specific result is shown with every ZIP lookup.

Independence & how we make money

This site is independently built and operated. It is not affiliated with any product manufacturer. Some product links are affiliate links — we may earn a commission if you buy through them — but your ZIP code result alone determines which product types we show, and timing recommendations never depend on what's linked.