What does this succession planner calculate?
This tool builds a sowing schedule from three inputs: the crop, the first sowing date, and the number of days between sowings. It lists every sowing with the date that batch should begin reaching maturity, based on the crop's typical days to harvest.
If you set your ZIP code, the planner also compares each batch's ready date against your median first fall freeze from NOAA climate normals, and flags the sowings that land past it.
What you will need
The crop
The crop list covers vegetables suited to repeat sowing: crops that mature quickly, produce over a limited window, or lose quality as they age. Each crop carries a suggested interval and a days-to-maturity value. Use the seed packet's maturity figure when it differs.
First sowing date
This is the date the first batch goes in, whether as seed in the ground or transplants set out. If the first sowing depends on your last freeze, find that window with the planting calendar or seed starting calculator, then use this planner for the batches that follow.
Interval between sowings
The interval controls everything. Too short and all batches mature together anyway; too long and you get gaps in supply. The suggested value suits the crop's harvest window, but adjust it for your household. A smaller family can stretch lettuce intervals to three weeks and still stay supplied.
Number of sowings
Each sowing needs its own space. Check that you have room for every batch before committing to a long schedule, or plan for an earlier crop to vacate the space.
How the planning works
The math is simple on purpose:
First sowing + interval × batch number = that batch's sowing date
Sowing date + days to maturity = expected ready date
A sowing of leaf lettuce on April 15 at a 10 day interval for six batches produces sowings on April 15, April 25, May 5, May 15, May 25, and June 4. At roughly 45 days to maturity, the first batch is ready about May 30 and the last about July 19.
The frost check works the same way in the other direction. If the median first fall freeze for a location is October 20, any batch whose ready date lands after October 20 gets flagged. You can still sow it under row cover, but it is no longer a sure thing.
Worked examples
Lettuce for a household
A gardener wants salads from mid-May through early July. First sowing April 10, interval 10 days, six sowings. The schedule runs to May 30, and the last batch is ready around mid-July. After that, summer heat makes lettuce unreliable, so the planner's list naturally ends where a fall sowing would pick up in August.
Bush beans through summer
Bush beans produce most of their crop in two weeks or so, then fade. A first sowing after the last freeze, followed by three more at 14 day intervals, gives four harvests spanning about six weeks. In a long-season climate, a second series can start in late summer.
Radishes without a glut
A whole packet of radishes sown at once means 200 radishes ripe in the same week. Sowing a short row every 7 days spreads the same seed packet across a month of harvests at very different table sizes.
What the frost flag means
The flag compares each batch's expected ready date with the median first fall freeze for the nearest NOAA station. It is a planning filter, not a verdict. Fast crops sown a few weeks before frost often still produce, especially under row cover, and the flag mainly tells you to stop counting on unprotected growth.
Cool-season crops also handle frost differently. Spinach and kale shrug off light freezes, while beans and cucumbers stop at the first touch. The flag treats them all the same, so apply crop knowledge on top of it.
Making the intervals work in practice
A schedule on paper fails if the beds cannot support it. A few habits keep it real:
- Reserve a small dedicated space for the crop instead of scattering sowings wherever there is a gap.
- Mark each sowing date on a calendar or set reminders. Missing one week breaks the chain.
- Sow smaller amounts more often rather than the same large row each time. The goal is steady supply, not maximum yield.
- Rotate the series to a different bed if soil-borne problems show up in the first batches.
Common mistakes
Sowing too much each time
The most common failure is treating every sowing like a full planting. A succession sowing only needs to cover the household's needs for its harvest window.
Forgetting the summer pause
Cool-season crops like spinach, lettuce, and cilantro stop cooperating in midsummer heat. Sowing them on schedule through July produces bolting plants, not harvests. Use heat-tolerant crops for midsummer slots or pause the series until August.
Ignoring maturity days on the packet
A 30 day radish and a 60 day carrot on the same interval behave very differently. The ready dates come from the crop's maturity figure, so use the packet value when it gives a more specific number.
When this planner may not be the right choice
Long-season crops grown once per year, such as tomatoes, peppers, and winter squash, do not suit interval sowing; staggered varieties do that job better. For one-off planting dates, the planting calendar and seed starting calculator give the full picture. For figuring out how many plants each batch needs, run the bed through the plant spacing calculator first.
Frequently asked questions
What interval should I use between sowings? Two to three weeks suits most quick crops like lettuce, radish, and bush beans. Shorten the gap in spring when everything grows fast and lengthen it toward fall as growth slows.
What does the frost flag mean? Flagged sowings are unlikely to mature before your median first freeze. They are warnings, not blocks: keep them if you want to gamble on a late crop under row cover, or drop them from the plan.
Should I keep sowing all summer? Not for cool-season crops. Lettuce, spinach, and radish bolt in real heat, so midsummer sowings produce bitter, stunted plants. Pause those crops through the hottest weeks and restart for fall.
