The August window: what to plant now for a winter harvest

The winter harvest is decided in the heat of August, when nobody has their mind on it. Heat is not what limits fall crops; light is. Here is how we time the plantings of our winter market garden, and the crops that deserve a bed this month.

Count back from the 10-hour day

The first rule of winter gardening: once day length drops below 10 hours, growth comes to a near standstill. At Ferme des Quatre-Temps, in Hemmingford, that moment arrives around November 1. After that, the tunnel becomes a big cold room we harvest from. Look up the date for your farm: Montréal is November 1, Portland November 3, Burlington November 5, Paris October 29, San Francisco November 20.

The rule we follow: a crop should reach 70 percent of its maturity before that date. Take its days to maturity (DTM), keep 70 percent, and count back. Tatsoi at 35 days needs 25, so it goes in by October 7. Spinach at 45 days and Hakurei turnips at 60 both go in by September 30.

Ten days late costs weeks

The closer you get to November 1, the more DTM climb. Tatsoi seeded on October 5 matures in about 35 days, like in summer. Seeded on October 15, it needs at least 50. DTM can even double depending on temperature and sunlight.

For cut-and-come-again crops like Salanova, arugula and Asian greens, plan two or three seedings seven to ten days apart. In winter, expect about three cuts per planting.

In the book, we tell you to draw this graph for your own crops after a winter of notes. Heirloom now gives you a head start. In Charts, open Direct seeding or Transplantation and click the curve icon on a crop's row: the curve shows how many days that crop takes to mature depending on the week you plant it, adjusted to your own farm's climate, day length included. It starts from the row's Average DTM, so change that number and the curve follows. Turn on Use climate-adjusted DTM on a planting and the Game Plan moves its harvest date to match.

What goes in during August

Storage carrots come first, sown at the end of July, and by August 10 under a caterpillar tunnel. We sow them in the garlic beds right after the garlic harvest; the straw that covered those beds for months leaves far fewer weeds. We harvest over a few weeks from November. They withstand a hard frost and stay in the field until the snow, and they get so sweet that they are a hot topic at the market. We always run out.

Outside under row cover, our dates in southern Quebec are August 1 for dandelion, komatsuna and senposai, and August 15 for kale, Salanova, mâche, Swiss chard and watercress. Claytonia goes in on August 20 and needs no cover. Salanova is the base of our winter mesclun and gives up to four cuts. Parsley has become a must-have winter crop: transplant it early, by August 30 even in a minimally heated greenhouse, so you have huge plants by November 1. Spinach, the star of the show, waits for September, like arugula, Asian greens, turnips and radishes.

Roots first, cold later

Winter crops need strong roots before the cold. Anything we transplant for winter goes into a 72-cell tray instead of the 128 we use in summer, so seedlings build a bigger root system in the mild weather. Then, around mid-November, we harden them off on purpose: we leave the covers off or open the tunnel to let the cold in, gradually, before real freezing temperatures arrive.

Have the covers ready

Our row cover, P19, lets through 85 percent of the light and adds 1.5 to 2°C (3 to 4°F). We spread it over hoops, and double or triple it on the coldest nights. Once days are under 10 hours, it stays on all the time. Set the hoops beside the beds when you plant, not the evening before a frost.

August is tiring. Plant anyway. Your customers will thank you in December.

-JM