Use the winter cold frame at the end of the season

It’s wonderful to be able to start plants months earlier than in the traditional garden, but the winter cold frame is equally useful at the end of the growing season. Mature vegetables can withstand a considerable amount of frost. Spinach, for example, will survive a 20 degree F night with no damage. A cold frame with insulation and a heat source is the key to extending the season.

As with winter gardening, the limiting factor is sunlight. For those intentionally planting to be able to harvest as long as possible into the fall and winter, aim to seed the plants so there’s enough time for them to reach a reasonable size while there is more than 10 hours of sunlight. Once the amount of sunlight dips below that amount, growth drops off and you’re mostly harvesting without substantial new growth.

When to plant the winter crop

To determine when to plant in the summer for a late season crop, look at the back of the seed packet. It will tell you how many weeks until maturity. Add a couple more weeks to mitigate for the waning sunlight. As an example, if lettuce is 4 weeks, plant it in early to mid-August to give it plenty of time to mature.

Harvesting greens in the winter cold frame – photo by Amy Grisak

Once the weather shifts, close the lid at night. At the beginning of the season, the warmth of the ground will typically be enough to keep the plants safe. But as the temperatures dip into the 20s or colder, turn on the light for additional protection.

At some point, plants will stop growing. For some, such as spinach, chard, and kale, leave them in the ground with the box covered and blanket over the top. This is often enough to carry them through until the days with sunlight begin to lengthen again. It is not unusual for these plants to resume growth. Leave carrots in the ground. Harvest them as needed throughout the winter.

Long-term winter gardening solution

It might take a half a day to build a winter cold frame. But, the effort is repaid with years of season extending capabilities. When the time of spring planting is accelerated or fall harvesting is delayed, there’s more time to enjoy your garden’s bounty – and less reliance on the supermarket’s wares.