What succession planting is
Succession planting means sowing the same crop several times, a couple of weeks apart, instead of all at once. Virginia Cooperative Extension puts it this way: for certain crops, "you may wish to do multiple plantings spaced every two to three weeks during the planting window to achieve a continuous harvest." A single sowing comes ready all at once; several short rows sown two weeks apart spread the same harvest over months.
Virginia Tech's planting guide (Table 5) recommends two or more plantings a year for lettuce, bush beans, beets, carrots, spinach, radishes, peas, cucumbers, summer squash and sweet corn. The planner covers every crop we have a published sowing interval for.
How the planner builds the schedule
Every date counts from your frost dates. Enter a ZIP code to use the nearest NOAA weather station (1991 to 2020 normals), pick your hardiness zone for the zone's median dates, or type in your own.
Sowing dates = first sowing + interval × 0, 1, 2 ... up to the last sowing date
- First sowing is the crop's direct-sowing time, counted in weeks from the last spring frost. Frost-hardy crops such as lettuce and radishes take the early end of that window (3 or 4 weeks before the frost). Tender crops such as beans and cucumbers take the late end.
- Interval is the published gap between sowings for that crop, low end first. You can change it for each crop.
- Last sowing is the latest date a sowing can still mature before the first fall frost: the frost date minus the slowest days to maturity. For frost-tender beans the planner also subtracts 3 weeks of picking (Utah State gives 2 to 3), so the last planting is not killed half picked. Beets use the published rule instead: stop 8 weeks before the first frost.
- Harvest window runs from the sowing date plus the fastest days to maturity to the sowing date plus the slowest, plus the picking time where it is published.
If a crop has no verified days to maturity (cilantro is one), the planner cannot set a last sowing date. It shows four sowings and lets you change the number.
"Average" frost dates are the median: half of years still see frost after the spring date. "Safer" is the 30% date that The Old Farmer's Almanac prints, and "safest" is the 10% date. A safer date moves the first sowing later and the last sowing earlier, so the season holds fewer sowings.
Worked example: lettuce in Minneapolis (ZIP 55401)
The nearest station for 55401 is Lower St Anthony Falls, 1.2 miles away. Its average last spring frost is Apr 23 and its average first fall frost is Oct 16.
Lettuce is direct sown 2 to 3 weeks before the last frost, so the first sowing is Apr 2. Johnny's Selected Seeds suggests sowing every 14 to 21 days; the planner starts at 14. Lettuce takes about 60 days from seed, so the last sowing that can mature before Oct 16 goes in on Aug 17.
That is ten sowings. At the default 5 ft per sowing and 8 inches between plants, each one is about 8 heads. Switch to "safer" dates (Apr 30 and Oct 10) and the season shrinks to nine sowings, Apr 9 to Jul 30.
The planner also shows the warning the crop notes carry: lettuce germinates poorly above 80°F, and summer heat turns it bitter. Virginia Tech plans three spring and three fall plantings of head lettuce rather than one every two weeks through summer. If your summers are hot, open the crop's settings and move the last sowing date earlier to stop before midsummer.
Succession planting chart: intervals by crop
For cucumbers we found no crop-specific interval, so the planner uses Virginia Tech's general two to three weeks. Virginia Tech also lists two to three spring and summer plantings of cucumbers and none in fall.
How to choose an interval
Short intervals suit fast crops: radishes stay prime for only a few days and go in every 10 days in Utah State's guide, and Johnny's sows spinach every 7 to 10. Carrots, which take 70 to 100 days, go in every 28 days in Utah State's guide. For a crop with a range, use the short end if you eat it steadily and want small, frequent harvests, and the long end if a gap of a week between harvests does not matter.
Row length sets the size of each harvest. Start with a short row per sowing and add more later, instead of one long row that all comes ready together.
Exports and next steps
Download the schedule as a spreadsheet (CSV) or as a calendar file (ICS) with one reminder per sowing, or print it with the chart. Exports use next season's calendar once this year's sowing season is past.
To decide how much row each crop needs in total, use the garden size calculator. For crops you start indoors before the first sowing, the seed starting calculator counts back from the same frost dates. To fit the rows into beds, open the raised bed planner.
