A Guide to Winter Harvest Crops & Overwintering for Spring Harvest
When temperatures and day length drop, your harvest season need not come to a full stop. As more growers construct high tunnels on their farms and participate in winter markets, we are frequently asked, "What can I plant to harvest in winter, and when should I plant it?"
To begin, it is helpful to distinguish between the two main winter growing strategies. The first group you harvest in winter, the second group you leave in place over the winter to produce an early spring crop.
- Winter Harvest Crops are planted in late summer or early fall, primarily in high tunnels, for harvest throughout the winter.
- Overwintered Crops are planted in the fall or winter, often outside in the field or under low tunnels, and left in place for the earliest possible spring harvest.
There is plenty of flexibility and overlap in the methods employed, including a combination of both strategies together.
Producing marketable crops in winter requires learning the correct planting window times for your location. Use the following guidelines while adjusting the techniques and timing to fit your practice. Remember to keep records, to determine what works best and improve upon your successes.
Ten hours of day light
The key to scheduling your plantings is to identify when your winter days reach less than 10 hours in length. It is during this darkest time of the year — referred to by Eliot Coleman as the "Persephone period" — that plant growth essentially stops. (You can obtain exact dates for your location using an app or website such as Rise or SunriseSunset.)
The goal is to seed your plants so they are at least 75% mature by the time the Persephone period begins.
Though plants may not grow appreciably thereafter, they can be harvested as needed while their maturity holds.
Careful scheduling allows you to control growth incrementally by planting at least two or three sowings at 7- to 10-day intervals. This will allow for crops to mature at different times and provide a longer harvest period. With well-timed, staggered plantings you can create a smooth transition from one harvest to the next for a steady supply through the winter. Multiple seedings also help you identify the best seeding dates for specific crops, and spread out the risk of crop failure due to unfavorable weather conditions.
Two neat tricks to get plants ready for the darkest days in high or low tunnels
- Transplant crops like spinach that are normally direct-seeded. Start the plants elsewhere and grow them to transplant size before planting them in your high tunnel, after your summer-producing crops have been removed.
- Establish hardy crops outside in late summer, then place a moveable tunnel over them, or construct a caterpillar tunnel over the crop as winter threatens.
Squeeze in even one more crop
In late winter, before you have harvested your winter crops, anticipate open bed space and what could be planted once the bed is available. As the end of the Persephone period draws near, you can reseed or transplant the openings. These winter sowings will be ready for harvest by early spring, often long before the same crop when grown outside.