Planting calendar
Indoor starts, outdoor planting windows, succession sowing and the latest planting dates for your crops, counted from your own frost dates.
The table reads the frost dates and crops from your setup. Rows are sorted by the first thing to do. A row marked This week has a window open today. Module 6 explains every column.
How many days you want to keep picking a crop before the first fall frost. No source we use gives a per-crop figure, so it starts at 0. A larger number moves every latest-planting date earlier. It is saved in this browser.
How the dates are counted
| Column | Rule | Source |
|---|---|---|
| Plant outdoors | Hardy crops: 2 to 4 weeks before your average last spring frost. Semi-hardy: 0 to 2 weeks before. Tender: around the date (cucumber and summer squash transplants wait until frost potential is over). Very tender: 2 or more weeks after. | Colorado State University Extension, CMG GardenNotes #720 Convention |
| Start indoors | The outdoor window, moved earlier by the crop's transplant age in weeks. | CSU #720 transplant ages; Cornell Cooperative Extension Rockland County for lettuce, kale and onion; University of Minnesota for basil Convention |
| Min. soil temp | The lowest soil temperature at which the seed germinates in laboratory tests. CSU says to measure at 8 a.m., 4 inches deep (beans at 6 inches). | Oregon State University Extension (Harrington data) Physical principle |
| Succession | Days between sowings for a steady harvest. | University of Kentucky Cooperative Extension, credited to Johnny's Selected Seeds Convention |
| Latest planting | First fall frost minus (days to harvest + 14-day fall factor + 14-day frost-tender factor for tender and very tender crops + your harvest period). For crops whose days to harvest count from transplanting, the seed-indoors date subtracts the longer transplant age as well. | Nebraska Extension G1343; Virginia Cooperative Extension 426-334 Convention |
| Garlic | No date. Plant cloves in fall, 4 to 6 weeks before the ground freezes; your extension service gives the local window. | University of Illinois Extension Ask the authority |
Where a source gives a range of days to harvest, the calendar uses the longer figure (kale 65, sweet corn 90), so a latest-planting date errs early. A crop marked does not fit has a latest planting date earlier than its spring planting window: from direct seed, it cannot mature between your two frost dates by the formula. Module 6 works through the options with a fictional example.
Where extension services disagree
Extension services publish different windows for the same frost classes. The calendar uses Colorado State's, and does not average them. If your own state's service publishes a calendar, use theirs: it was written for your conditions.
| Class | Colorado State #720 | Purdue HO-186 (Indiana) |
|---|---|---|
| Hardy | 2 to 4 weeks before the last frost | 4 to 6 weeks before |
| Semi-hardy | 0 to 2 weeks before | 2 to 4 weeks before |
| Tender | Around the last frost date | After the last frost |
| Very tender | 2 or more weeks after | 2 or more weeks after |
Utah State University Extension groups crops A to D relative to the last frost with its own offsets. Virginia Cooperative Extension's 426-331 gives windows by region of Virginia. Both are linked in the resource library.
Assumptions
- Your frost dates are the ones you entered. The commonly published date is the 50 percent date: half of past years had a later frost. If you want less risk, enter the 10 percent date instead (Module 2).
- Days to harvest are general figures; your packet's figure for your variety is better. Change the plan, not the source.
- The calendar cannot see this year's weather. A cold spring moves everything later. Soil temperature and the ten-day forecast overrule the table.
- Where your area rarely or never frosts, the calendar computes no dates, because these frost-based conventions do not describe your season.
These are planning windows from published conventions and your frost dates, not instructions for this year's weather. Check the soil thermometer and the forecast before each planting, and keep row cover on hand for a late frost.