What the calendar shows
The planting calendar shows a crop window from a cited state extension guide. Ten states have a guide. The publisher, the title, and the date it was read are printed with the crop. Other states still show the station’s frost dates.
Week offsets follow the guide’s wording. When a guide says “weeks after the frost-free date” and does not name a 10%, 50%, or 90% level, those weeks are applied to the median last 32°F date, and the page says so. Weeks before the first freeze use the median first 32°F date. A month named without a day is expanded to the first and last day of that month, and the page says so. A phrase such as “late May,” without a start and an end, stays a phrase. An “or” or a slash between two week counts is one continuous span. The methodology page lists each of those readings.
How to use it
Look up a ZIP first. If that state has a guide, choose a crop. If the guide splits the state into regions, choose the region that matches the guide’s map, not a region you wish you were in. The seed-packet card repeats the printed label and, where the offset can be applied, the resulting month and day at this station. Two cities in the same state can show different days because their stations have different median frost dates. The week counts do not change.
Texas has an extra fall chart. When the ZIP’s zone maps to a region in that chart’s table, the calendar can also print the average fall planting date from that table. It names the chart. It does not mix that date into the spring window.
Days to harvest, when the same guide prints them, are shown as a note. They are the guide’s range for the crop, not a measurement from your packet. If your packet disagrees, the packet is the one to use in the fall and seed tools, which ask you to type the number.
A city planting calendar uses the same layout with the station already filled in. The list of guides is on the methodology page.