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Regional Calendars, Climate & DataData Sources for Planting Calendars
A planting calendar is only as good as the data under it. These are the public sources worth knowing, and what each one can and cannot tell you.
Key points
- NOAA, regional climate centers and local NWS offices supply frost and climate data.
- USDA NASS gives typical timing, and RMA gives insurance dates.
- Extension guides supply crop thresholds and varieties for your area.
- Check years, thresholds and risk levels before comparing sources.
- Document each source, its threshold and its years before mixing numbers.
Which sources give frost and freeze data?
NOAA's NCEI publishes freeze and frost probability tables at thresholds of 36, 32 and 28 degrees F, as NC State Extension explains, with dates at several probability levels. National Weather Service local offices, such as the one in Medford, Oregon, publish frost and freeze charts for their areas. The Midwestern Regional Climate Center freeze date tool covers counties in the north-central and northeastern states, with data from 1950 and thresholds from 20 to 40 degrees F.
Check which years each source covers and what threshold it uses.
If a source gives frost dates for a single point, check how far that point is from your farm and whether it sits in a similar setting. Distance in miles matters less than differences in elevation and exposure.
Where do you find climate normals?
NCEI's U.S. Climate Normals are 30-year averages, currently for 1991 to 2020, covering temperature, precipitation, growing degree days, growing season length and many other statistics. They are updated every ten years and serve as a benchmark for comparing current weather.
Regional climate centers and state climatologists provide station and county tools built on the same underlying data, often through the Applied Climate Information System.
If you need data at a very fine scale, ask your state climatologist or extension office whether a state network or local mesonet exists, since some states run their own weather stations with soil temperature readings.
- NOAA NCEI climate normals
- Regional Climate Centers
- State climatologist offices
- National Weather Service local offices
What do USDA sources add?
USDA NASS publishes usual planting and harvesting dates for field crops and for vegetables, and weekly Crop Progress reports. The USDA Plant Hardiness Zone Map shows average annual extreme winter minimums, which helps with perennial crops but does not give frost dates or planting dates. USDA Climate Hubs offer regional guidance on adapting timing and crop choices.
The Risk Management Agency publishes insurance planting dates by crop and county, which can limit when planting is eligible. Always read the page that describes how a dataset was built, since the method explains most of the differences between sources.
How do extension guides fit in?
Land-grant extension services produce the most practical local guidance: planting guides, variety trials, soil temperature articles and pest advisories. Kansas State publishes a Kansas Crop Planting Guide, Iowa State publishes planting date articles for corn and soybeans, and University of California gives regional planting tables for vegetables.
These are the sources to use for crop-specific thresholds and varieties.
Extension publications are usually the most current for crops, so check the publication date and look for newer versions before you rely on a guide.
How should you combine sources?
Use climate data for frost anchors and heat accumulation, USDA records for typical timing, extension guides for crop thresholds, and your own records for calibration. Where sources disagree, look at the years, thresholds and risk levels each used.
Keep a short list of the sources you rely on and the date you last checked them.
Write down for each source what it covers, what threshold it uses, which years it includes and when it was last updated. A short table like this saves you from mixing incompatible numbers later.
What are the cautions?
Data from older publications may not reflect current varieties or practices. Station data may not match your terrain. Modeled values such as soil temperature or gridded forecasts are estimates. Web calendars from commercial sites often do not state their method, so verify their dates against an extension or NOAA source.
When in doubt, call your county extension office. They usually know which sources local growers trust. Review your source list every year and drop any that have not been updated.
Which sources do you check during the season?
Before planting, check the National Weather Service forecast for your area, local soil temperature readings and your own thermometer. During the season, the U.S. Drought Monitor shows dryness at a glance, and USDA NASS Crop Progress shows how planting and harvest are moving across the country compared with earlier years.
After the season, add your own results to your records. Over time, your own data becomes the most useful source of all.
Sources and further reading
Last reviewed: November 2026. Educational information, ranges only. Confirm timing with your county extension office.