The window sets the interval, not the other way round
Everyone knows succession sowing means putting a crop in every few weeks. The number of weeks is not a preference, it is arithmetic: if one planting is worth picking for three weeks, sowings more than three weeks apart leave a gap, and sowings closer than that just overlap. Sixteen weeks of supply on a three week window needs six sowings, and six sowings cover eighteen weeks — two weeks of deliberate overlap that absorbs one slow planting without a hole in the middle of the season.
Which means the input worth measuring is the window. Growers guess it, and they usually guess it long, because the plants are still alive at the end. The question is not whether there is anything left on them, it is how long they are worth cutting at the quality you sell, which is a shorter answer.
Sowings compress even when harvests do not
This is the part that catches people. Spread six sowings evenly across sixteen weeks and the harvests start 18.2 days apart. But if the last sowing takes 25 percent longer to reach the first pick than the first one did — 69 days against 55, as the days shorten — then each sowing has a longer run at the same finish line, and the sowing dates have to tighten to compensate. At the defaults they land 15.45 days apart, 2.75 days closer than the harvest interval they produce.
Sowing on the harvest interval and hoping is the standard way to find yourself short in September. The effect gets larger the bigger the seasonal add-on, and it is worth checking against your own records: the gap between what you sowed and when it actually came in, for the late plantings, is the number the creep field is trying to capture.
| Sowing | Days to first pick | Sow on day | Days after the previous sowing |
|---|---|---|---|
| 1 | 55 | -55 | — |
| 2 | 58 | -39.6 | 15.45 |
| 3 | 61 | -24.1 | 15.45 |
| 4 | 63 | -8.6 | 15.45 |
| 5 | 66 | 6.8 | 15.45 |
| 6 | 69 | 22.3 | 15.45 |
Day 0 is the day you want the first pick. The last sowing goes in three weeks after the harvest has already started, which is worth knowing when you are working out what else the propagation space is doing that month.
Ground per sowing, not ground per season
Ninety units a week across a three week window with 20 percent added for culls is 324 units from each sowing, and at 1.4 units a bed foot that is 231 bed feet. Rounded to whole 100 foot beds it is three beds — 300 feet planted for 231 needed, which is 30 percent going to rounding, six sowings over: 1,800 bed feet of ground prepared for 1,389 of crop. Shorter beds round tighter, and this is one of the clearest arguments for sizing beds to the smallest planting you actually make rather than to the tractor.
Where this fits
The quantity side of a whole crop plan is the CSA share planting plan calculator, which works out bed feet across a crop list rather than the calendar of one crop. What the sowings turn into on a harvest morning is the market harvest pick list calculator. For propagation space before the transplants go out, see the propagation tray and bench capacity calculator, and for covered ground, the hoop house sizing calculator.
Questions people ask
How do I measure the harvest window?
Pick one planting and keep a note of the date of the first cut you were happy to sell and the date of the last one. That interval is the window, and it is usually shorter than the interval between the first cut and the plants dying. If you have never recorded it, start with a figure you think is slightly short rather than slightly long, because a short window produces more sowings and an overlap, while a long one produces a gap you cannot fix once you are in it.
Why do the sowing dates get closer together?
Because a later sowing takes longer to reach the first pick as the days shorten and cool, so it has to start earlier relative to when you want it. If the last sowing needs 69 days where the first needed 55, that fourteen day difference has to come out of the sowing intervals, and across five intervals it tightens each one by nearly three days. The size of the effect depends on how far into the season you are going and how much a crop feels the change.
What is the seasonal add-on and where do I get it?
It is how much longer the last sowing takes to reach picking than the first one did, as a percentage. There is no published number for it worth using, because it depends on your latitude, your crop, whether the planting is covered and how the autumn goes. The way to get it is to look at your own records: compare a spring sowing and a late summer sowing of the same thing and see how the actual days to first pick differed. If you are only sowing into a rising season, put zero.
Does this handle a crop that is cut more than once?
Yes, as long as the window and the yield per bed foot both describe the whole life of the planting. A cut-and-come-again crop that gives three cuts over four weeks has a four week window, and the units per bed foot figure should be the total across all three cuts, not one of them. The page has no idea how many individual picks happen inside the window and does not need to.
Can I turn the day numbers into actual dates?
Yes, by picking the date you want the first pick and counting from it — day zero is that date, negative numbers are before it. What the page will not do is check that those dates make sense where you are, because the last useful sowing date, the first and last frost and how a crop behaves in your autumn are local enough that only your own records and your extension service are worth using. A calendar that works forty miles away can be a week wrong on your ground.