Cold Frame Greenhouses

What are Cold Frame Greenhouses?

A cold frame greenhouse is a simple, unheated outdoor structure designed to protect plants from cold weather while still allowing exposure to sunlight. It acts as a miniature greenhouse, creating a microclimate that extends the growing season. Cold frames are typically low-profile boxes with a transparent lid that opens to allow ventilation. The transparent top, usually made of glass or rigid plastic, allows sunlight to enter and warm the interior, while providing insulation against cold temperatures outside.

Benefits of Using Cold Frames

Cold frames offer several advantages for gardeners and plant enthusiasts:

1. Season Extension: By providing a protected environment, cold frames allow gardeners to start seeds earlier in spring and continue growing cool-weather crops later into fall or even winter in some climates.
2. Hardening Off: Cold frames are ideal for hardening off seedlings started indoors, gradually acclimating them to outdoor conditions before transplanting.
3. Frost Protection: The insulating properties of cold frames can protect plants from light frosts, allowing for earlier planting and later harvesting.
4. Versatility: Cold frames can be used for seed starting, growing cool-weather crops like lettuce and spinach, overwintering hardy plants, or providing protection for tender perennials.
5. Space-Saving: With their compact size, cold frames are perfect for small gardens, patios, or balconies where space is limited.

Types of Cold Frame Greenhouses

Cold frames come in various types and can be constructed from different materials:

1. Wooden Cold Frames: Traditionally, cold frames were built with wood frames and glass or plastic lids. These can be permanent or portable structures.
2. Plastic Cold Frames: Lightweight and inexpensive, plastic cold frames are often made from rigid plastic or polycarbonate panels and are easy to assemble and move.
3. Mini Greenhouses: Some cold frames are designed as small, portable greenhouses with shelving or growing racks inside for seed starting or housing potted plants.
4. Raised Bed Cold Frames: These cold frames are built directly over raised garden beds, providing protection for in-ground crops.
5. Window Cold Frames: Repurposed old windows or storm windows can be used to create simple, cost-effective cold frames.

Construction and Placement

When constructing or placing a cold frame, consider the following factors:

1. Orientation: Position the cold frame to face south or southeast to maximize sunlight exposure, especially during winter when the sun is lower in the sky.
2. Slope: Angle the lid or top slightly to allow for better solar exposure and to shed rain and snow more easily.
3. Ventilation: Ensure the cold frame has vents or the ability to open the lid for ventilation on warm days to prevent overheating.
4. Insulation: Adding insulation around the sides or underneath the cold frame can improve its ability to retain heat.
5. Drainage: Provide proper drainage to prevent waterlogging, which can lead to root rot and other issues.

Maintenance and Care

To keep your cold frame greenhouse functioning optimally, follow these maintenance tips:

1. Ventilation: Open the lid or vents on warm, sunny days to prevent overheating and provide air circulation.
2. Watering: Monitor soil moisture levels and water plants as needed, being careful not to overwater.
3. Cleaning: Regularly clean the transparent lid or top to maximize light transmission.
4. Pest Management: Inspect plants for pests and diseases, and take appropriate action if necessary.
5. Winter Protection: In colder climates, add an extra layer of insulation, such as bubble wrap or row covers, during extreme cold snaps.

With proper construction, placement, and maintenance, a cold frame greenhouse can be a valuable asset for any gardener, extending the growing season and providing a protected environment for plants to thrive.