Crop planning in the Southern Hemisphere: why northern plans break

While I seed my first flats of the spring, the growers in Victoria, in Canterbury and in the Cape are harvesting the last of their summer and starting to plan the next season. This one is for them. Most crop plans, templates and planting calendars are laid out on a year that runs from January to December, and down under that year cuts your best season in half. The good news: the market gardener method, biointensive and regenerative, is not tied to one climate. What has to change is how you lay out the plan.

The calendar-year trap

A northern season fits inside one calendar year. Yours does not. The tomatoes you seed in the nursery in September go into the field in October and give until well after New Year. On a plan that runs from January to December, that one planting is cut on December 31: half of it on this year's page, half on next year's, and neither page shows that the bed is taken. Shifting a northern plan by six months does not fix it; it only moves the cut.

So start your planning year when your season starts. Make the first week of July week 1 of your plan, not the first week of January, and set your frost dates from your own area's weather records, not from a northern calendar: the dates in my book come from our farm in southern Quebec, zone 6. Every summer planting then sits whole on the same page, from the nursery to the last harvest, and your successions, bed rotation and cash flow read in the order you actually live them.

The days to maturity on the packet are not your days

The days to maturity printed on a seed packet is a standard number, often measured in steady conditions (we explained why in Why Seed Packets Lie). A plant responds to heat and day length, so the same crop does not grow at the same speed at the start, the middle and the end of your season. For vegetables transplanted early in spring or late in the fall, the days to maturity have to be adjusted for slower growth: we add five to ten days to the first and last plantings of a succession, and late in the fall, days to maturity can double.

For your last plantings, count back from light as much as from frost. They should reach about 70 percent of their growth before the day falls under ten hours. That rule does not care which hemisphere you farm in; only the month changes.

Let Heirloom do the math

This is where plans on paper fall apart: forty crops, each with its own dates, each shifting with the season. Heirloom does that work for you now. In your farm settings, under Season & climate, set the Planning season to start in July: your plans, tasks and reports then run from July to June. Heirloom also estimates your last and first frost dates from ten years of weather at your address, with the seasons flipped south of the equator; check them against what you know of your land, then Use these dates.

Then, in the planting window, turn on Use climate-adjusted DTM: days to maturity follow your own farm's climate, week by week, from the heat your crops will get (the growing degree days) to the length of the day where you are. Your first and last plantings get their longer days on their own, and a tomato planting that crosses New Year stays whole on your Game Plan, from the nursery to the last harvest.

-JM