Can cold frames extend the growing season for greens?

Extending the Growing Season

Cold frames work on the principle of insulation and passive solar heating. They consist of a transparent or translucent lid that allows sunlight to enter, a frame to support the lid, and a bottom that can be covered with soil and plants. By using a cold frame, you can extend the growing season for greens like kale, spinach, and lettuce by 2-6 weeks in cold climates.

Design and Construction Considerations

When designing and building a cold frame, consider the following factors: size, orientation, and materials. A cold frame should be at least 2-3 feet wide and 4-6 feet long to allow for good air circulation and easy access. The frame should face south to receive maximum sunlight, and the lid should be adjustable to allow for ventilation. Use durable materials like wood, metal, or recycled plastic to build the frame, and make sure it is well-insulated to retain heat.

Maintenance and Plant Selection

To get the most out of your cold frame, maintain a consistent temperature between 40-60°F (4-15°C) by covering the top with a layer of straw or burlap at night and uncovering it during the day. Choose cold-hardy varieties of greens like ‘Winterbor’ kale, ‘Space’ spinach, and ‘Loose-Leaf’ lettuce, which can tolerate light frosts. Plant seeds 1-2 inches apart in late spring or early fall, and add a layer of mulch to retain moisture and suppress weeds.