Cold Frame Greenhouses

What is a Cold Frame Greenhouse?

A cold frame greenhouse is a low, simple structure used to protect plants from harsh weather conditions, extend the growing season, and provide a sheltered environment for growing vegetables, flowers, and other plants. Cold frames are often used to start seedlings early in the spring or to grow hardy crops into the fall or winter months.

Typically, a cold frame greenhouse consists of a transparent cover (usually glass, acrylic, or clear plastic) that allows sunlight to enter, trapping heat inside. The frame itself is generally made of wood, metal, or PVC. Cold frames are designed to trap solar heat during the day, and while they do not have heating systems like traditional greenhouses, they retain enough warmth to protect plants from frost during colder weather.

Cold frame greenhouses are different from full-scale greenhouses in that they are much smaller, often built close to the ground, and do not require extensive construction or a permanent foundation.

Benefits of Cold Frame Greenhouses

Cold frame greenhouses offer a wide range of benefits for gardeners looking to extend their growing season and protect their plants. Here are the key advantages:

1. Extended Growing Season

One of the primary reasons gardeners use cold frame greenhouses is to extend the growing season. In many regions, cold temperatures can limit the types of plants that can be grown and the time of year in which they can be grown. Cold frames act as a barrier against frost and provide an insulated environment that allows gardeners to start growing earlier in the spring and continue growing into the fall or winter.

For example, with a cold frame, you can begin planting seedlings long before the last frost date in your area. Similarly, you can continue growing cold-tolerant crops, like lettuce, kale, and carrots, well after the first frost of the year.

2. Protection from Harsh Weather

Cold frame greenhouses protect plants from extreme weather conditions such as frost, heavy rain, and strong winds. By creating a barrier between your plants and the elements, cold frames reduce the likelihood of plant damage from freezing temperatures or sudden weather changes.

In colder climates, a cold frame can provide protection against late-season frosts in the spring and early-season frosts in the fall. This makes them particularly valuable for gardeners in regions where unpredictable weather can threaten the survival of tender plants.

3. Improved Seedling Success

Starting seeds indoors can be tricky, especially if you don’t have access to a greenhouse or grow lights. Cold frame greenhouses offer an excellent alternative by providing a natural environment where seedlings can get the sunlight they need while being protected from the elements. The consistent temperature inside a cold frame is perfect for germinating seeds and growing strong, healthy seedlings before transplanting them outdoors.

4. Energy Efficiency

Cold frame greenhouses are highly energy-efficient since they rely on natural sunlight to heat the structure. Unlike traditional greenhouses, which often require electricity or other forms of energy to maintain temperatures, cold frames rely solely on solar energy. During the day, sunlight enters through the transparent cover and warms the air inside the frame. At night, the structure retains the heat, keeping plants warm without any added energy costs.

5. Cost-Effective

Cold frames are an affordable alternative to full-scale greenhouses. Because they are smaller and require fewer materials, the cost of building or purchasing a cold frame is significantly lower than that of larger greenhouse structures. This makes cold frames a great option for gardeners on a budget or those with limited space who don’t need the extensive growing area offered by larger greenhouses.

Additionally, cold frames can be made with simple materials such as old windows, wood, or recycled plastic, further reducing the cost.

6. Space Efficiency

Cold frames are compact and ideal for smaller gardens or urban areas with limited space. Their low profile means that they can be placed in a variety of locations, including small backyard gardens, patios, or even on rooftops. For gardeners with limited growing space, a cold frame provides an efficient way to grow more plants without taking up much room.

7. Ease of Use

Cold frames are relatively easy to set up and maintain. They do not require complex systems like ventilation, watering, or heating systems that traditional greenhouses may need. Most cold frames can be assembled with basic tools and materials, and they require minimal maintenance throughout the growing season.

Types of Cold Frame Greenhouses

Cold frame greenhouses come in various designs and sizes, and the right one for you will depend on your needs, available space, and budget. Here are the most common types of cold frame greenhouses:

1. Traditional Cold Frame

The traditional cold frame greenhouse typically consists of a simple wooden or metal frame with a hinged, transparent lid that can be opened to allow for ventilation. The frame is low to the ground, allowing the structure to capture maximum sunlight. These cold frames are easy to build and can be customized to fit the available space in your garden.

Features:

• Simple construction with a transparent lid (glass, acrylic, or clear plastic).
• Hinged or removable lid for ventilation.
• Great for small-scale gardening and protecting individual plants or seedlings.
• Low-maintenance and cost-effective.

Best for:

• Beginner gardeners.
• Small gardens or raised beds.
• Protecting a few plants or growing a limited number of seedlings.

2. PVC Cold Frame

PVC cold frames are an affordable and lightweight option that use a PVC pipe frame covered with clear plastic sheeting or polyethylene. These cold frames are easy to assemble and can be customized to any size or shape. PVC cold frames are particularly suited for gardeners who need a flexible structure that can be easily moved or adjusted.

Features:

• PVC pipe frame with clear plastic covering.
• Lightweight and easy to assemble.
• Customizable and portable.
• Affordable and effective.

Best for:

• Budget-conscious gardeners.
• Smaller or temporary growing spaces.
• Moving the cold frame around to optimize sunlight exposure.

3. Mini Cold Frame

Mini cold frames are compact and designed for gardeners with limited space. These cold frames are often small enough to fit on balconies, patios, or smaller garden plots. They typically come with a transparent lid for capturing sunlight and protecting plants from frost.

Features:

• Small and compact design.
• Ideal for small-scale planting or seed starting.
• Often made from plastic or acrylic materials.
• Portable and easy to set up.

Best for:

• Urban or apartment gardening.
• Balcony or patio gardening.
• Starting seedlings or growing herbs and small plants.

4. Raised Bed Cold Frame

A raised bed cold frame combines the benefits of a raised garden bed with the protection of a cold frame. These cold frames are built on top of an existing raised bed structure, providing additional protection for plants while allowing for deeper root growth. Raised bed cold frames are ideal for gardeners looking to grow vegetables or flowers in a more controlled environment.

Features:

• Built on top of raised garden beds.
• Provides protection from frost while allowing for deep root growth.
• Can be constructed with wood, metal, or other materials.
• Excellent for growing vegetables, herbs, and flowers.

Best for:

• Raised bed gardeners.
• Growing a variety of vegetables and flowers.
• Gardeners with a moderate amount of space.

How to Set Up a Cold Frame Greenhouse

Setting up a cold frame greenhouse is relatively simple and can be done with a few basic materials. Here’s how you can set up your own cold frame:

Step 1: Choose the Right Location

Select a sunny spot in your garden where your cold frame will receive at least 6-8 hours of sunlight each day. Ideally, the site should be sheltered from strong winds, as cold frames are relatively lightweight and may be vulnerable to wind damage. Avoid low-lying areas where frost is likely to collect.

Step 2: Build or Purchase Your Cold Frame

You can either purchase a pre-made cold frame greenhouse or build one yourself. If you're building it, use materials such as wood, PVC, or metal for the frame. Use clear plastic, acrylic, or glass for the lid. If you're purchasing one, look for a design that suits your available space and budget.

Step 3: Prepare the Soil

Before placing your cold frame, make sure the soil beneath it is well-draining and free of rocks or debris. If you're planning to use the cold frame for growing, you may want to amend the soil with compost or other organic matter to improve fertility.

Step 4: Place the Cold Frame

Place the cold frame in the chosen location, ensuring that it is positioned to capture maximum sunlight. If you have a hinged lid, make sure it can be easily opened for ventilation.

Step 5: Ventilation and Watering

To maintain healthy growing conditions, ensure that your cold frame is well-ventilated. Open the lid periodically to release excess heat and moisture, especially during warmer days. Water the plants as needed, making sure not to overwater, as cold frames retain moisture effectively.

Maintaining Your Cold Frame Greenhouse

Proper maintenance of your cold frame is essential to ensure that it continues to function effectively. Here are some maintenance tips:

1. Check for Leaks: Periodically check for any gaps or leaks in the structure. Repair any damaged areas to maintain a sealed environment.
2. Ventilation: Open the lid regularly, especially on sunny days, to prevent overheating.
3. Winter Care: In colder months, ensure that your cold frame is properly insulated. Use additional covers, like blankets or tarps, if necessary, to provide extra warmth.
4. Cleaning: Clean the cover of your cold frame regularly to ensure that sunlight can pass through freely.