Introduction to the Cold Frame Greenhouse

A cold frame greenhouse is the simplest and most cost-effective method to extend your growing season.  It is a small, unheated greenhouse that’s designed to trap heat and protect plants from cold weather. You can easily build a cold frame greenhouse with scrap materials or purchase one ready to use.

One of the advantages of a cold frame greenhouse is that it’s relatively easy and inexpensive to build. Unlike a traditional greenhouse, which requires a lot of materials and can be quite costly, a cold frame can be constructed using simple materials such as PVC pipe and clear plastic sheeting or wood and recycled windows. This makes it a great option for gardeners who are on a budget or who don’t have a lot of space to work with.

Another benefit of a cold frame greenhouse is that it allows you to start your plants earlier in the season. By providing a warm, protected environment, you can start seeds and seedlings weeks or even months before you would be able to plant them outside. This can be especially helpful if you live in a colder climate with a short growing season. Overall, a cold frame greenhouse is a versatile and effective tool for any gardener looking to extend their growing season and protect their plants from the elements.

Cold Frame Greenhouse Basics

A cold frame greenhouse extends the growing season for plants by providing a protected environment. It is typically made of wood, glass, plastic, or polycarbonate, and can be insulated or not, depending on the climate.

The cold frame creates a microclimate that is warmer than the surrounding environment, while still allowing for ventilation to prevent overheating. This is achieved by using clear materials that allow sunlight to enter, and by using features such as vents that can be opened or closed to regulate the temperature.

You can build your own cold frame using simple materials or buy one. Prices range from less than $100 to more than $1,000.  They be small and round or larger and rectangular and are a great option for gardeners who want to extend their growing season without investing in a full-sized greenhouse.

Overall, a cold frame greenhouse is a useful tool for any gardener who wants to grow plants outside of the normal growing season. With a little bit of knowledge and some basic materials, you can create a simple and effective structure to protect plants from the cold and provide a longer growing season.

How to Build a Cold Frame Greenhouse

If you’re looking to extend your growing season, building a cold frame greenhouse is an excellent solution. In this section, I will guide you through the materials and construction steps needed to build a cold frame greenhouse.

Materials and Tools

Materials

• Brick, stone or wood (cedar is a good option) for the sides of the frame
• Wood for the top of the frame
• Glass, plastic, or twin walled polycarbonate (reclaimed windows work well)
• Hinges and hardware
• Screws
• Gravel if needed (for drainage)

Tools

• Circular saw
• Drill
• Masonry tools if using brick or stone
• Screwdriver or bit

Construction Steps

1. Determine where you will place your cold frame greenhouse. It can sit on well-drained ground, concrete or other surface. You may want to place the frame on bricks to extend the life of the wood.
2. Measure and cut the wood to the desired dimensions of your cold frame greenhouse. Make sure to cut four pieces for the frame and two additional pieces for the lid. It works best to build it so the lid has a slope. If you are using reclaimed windows, build the frame to fit under the windows.
3. Assemble the frame using wood screws and a drill.
4. Cut the glass or plastic to fit the dimensions of the frame. If using reclaimed windows, make sure to remove any old paint or debris.
5. Attach the glass or plastic to the frame using hinges and hardware. This will allow you to easily lift the lid for ventilation and access to your plants.
6. Place a layer of gravel at the bottom of the cold frame greenhouse for drainage.
7. Once the construction is complete, place your cold frame greenhouse in a location that receives ample sunlight and is protected from harsh winds.

Here is a good tutorial for building a cold frame greenhouse.

Planting and Growing in Cold Frames

Choosing the Right Plants

When it comes to planting in cold frames, it’s important to choose the right plants that can withstand colder temperatures. Vegetables such as spinach, beets, carrots, lettuce, kale, corn, greens, cabbage, radish, salad greens, onions, arugula, broccoli, chard, and radishes are all great options for planting in cold frames. These plants can thrive in the cooler temperatures and provide a bountiful harvest. You can also use the cold frame to start more sensitive plants such as squash.

It’s important to note that not all plants will grow well in cold frames. Plants that require a longer growing season or warmer temperatures, such as tomatoes and parsnips, may not be suitable for planting in a cold frame. Be sure to research the plants you plan to grow and ensure they are suitable for colder temperatures.

Planting and Care Tips

Proper soil preparation is the key to success with a cold frame greenhouse. The soil should be well-drained and have adequate moisture. You can add compost or other organic matter to the soil to improve its quality.

You also need to consider sunlight and temperature. Cold frames should be placed in a location that receives ample sunlight, especially during the winter months when sunlight is limited. You can use a shade cloth to protect the plants from excessive sunlight during the warmer months. In addition to that, you will have to  monitor the temperature. If freezing is a threat, you can us straw bales, blankets or even debris to provide extra insulation. In hot weather, be sure to open the frame so you don’t cook your plants. 

Watering and drainage are also important considerations when planting in a cold frame. The soil should be moist but not waterlogged, and the frame should have adequate drainage to prevent water from accumulating.

When planting seedlings, make sure they are well-established before placing them in the cold frame. Dormant plants can also be planted in cold frames during the winter months to help them germinate.

Here is a concise guide if you want more detail on how to make the most of your cold frame greenhouse.

Planting in a cold frame is an efficient, inexpensive way to  extend the growing season and provide a bountiful harvest. By choosing the right plants and providing proper care, you can enjoy fresh veggies even during the colder months.

Benefits and Drawbacks of Cold Frame Greenhouses

Cold frame greenhouses are a great way to extend the garden season and protect crops from pests and harsh weather conditions. However, there are both benefits and drawbacks to using a cold frame greenhouse.

Benefits

• Protection: Cold frame greenhouses protect crops from pests, frost, and harsh weather conditions. The plastic cover provides insulation, keeping plants warm and dry.
• Mini Greenhouse: Cold frame greenhouses are a great way to start seedlings early in the season. They provide a mini greenhouse environment, allowing plants to grow and thrive before being transplanted outside.
• Harvest: Cold frame greenhouses can extend the garden season, allowing for a longer harvest period. Fresh vegetables can be grown well into the fall and winter months.
• Fresh: Cold frame greenhouses provide fresh vegetables year-round, even in areas with limited space.
• Money: Cold frame greenhouses are an inexpensive alternative to traditional greenhouse structures. They require minimal maintenance and are durable, lasting for many years.

Drawbacks

• Rust and Rot: Some cold frame greenhouse structures may rust or rot over time, reducing their durability.
• Limited Space: Cold frame greenhouses have limited space and may not be suitable for larger operations.
• Pests: Cold frame greenhouses may still be susceptible to pests, which can damage crops.
• Maintenance: Cold frame greenhouses require some maintenance, such as replacing plastic covers and cleaning the structure.
• Monitoring: Cold frames don’t lend themselves to automatic monitoring systems. You have to be diligent with them.

In conclusion, cold frame greenhouses have benefits for both the commercial grower and the self-sufficient gardener. They provide fresh vegetables year-round, extend the garden season, and are an inexpensive alternative to traditional greenhouses. However, they do have some drawbacks, such as limited space and the need for maintenance.

Advanced Techniques and Tips

Ventilation is Key

One of the most important things to keep in mind when using a cold frame greenhouse is ventilation. Without proper ventilation, your plants can quickly become overheated and die. Excessive humidity and moisture can also wreak havoc on your plants. The hinged lid makes adjusting the ventilation simple, but you have to be diligent about monitoring the environment inside the cold frame.

Insulation is Important

Another important factor to consider is insulation. Greenhouses with insulated walls and roofs are better at maintaining a consistent temperature, which is crucial for creating a stable microclimate for your plants. Remember that insulation doesn’t have to be built in. It can be as simple as using straw or hay bales, blankets, or debris.

Overwintering and Nursery

If you plan on using your cold frame greenhouse for overwintering or as a nursery, make sure to adjust the temperature accordingly. Leeks, for example, prefer cooler temperatures, so you may need to adjust the ventilation and insulation to keep the temperature within the optimal range.

Clear vs. Translucent Greenhouses

When choosing a greenhouse, consider whether you want a clear or translucent design. Clear greenhouses allow more light in, which can be beneficial for plants that require a lot of sunlight. Translucent greenhouses, on the other hand, provide more diffuse lighting, which may be better for some plants. Of course you can always use shade cloth with clear panels to regulate the amount of light. 

Frequently Asked Questions

What are the advantages and disadvantages of using a cold frame greenhouse?

A cold frame greenhouse is an excellent way to extend the growing season and protect plants from harsh weather conditions. The biggest advantage is that it allows you to start your plants earlier in the season and grow them later into the fall. It also provides protection from strong winds, heavy rain, and snow. And it does all this at a low cost. However, it can be difficult to regulate the temperature inside the cold frame. You have to be diligent, especially during very hot or very cold weather. 

What is the difference between a cold frame and a greenhouse?

A cold frame is a simple, low-cost structure that is usually made of wood, plastic, or metal and covered with a clear material such as glass or polycarbonate. A greenhouse, on the other hand, is a larger, more complex structure designed to provide a controlled environment for plants, with features such as heating, cooling, and ventilation systems. Generally speaking, you can walk into a greenhouse. You would have to be a very tiny person to walk into a cold frame. 

Can a cold frame get too hot for plants?

Yes, a cold frame can get too hot for plants, especially during the summer months. To prevent this from happening, it’s important to provide proper ventilation by opening the lid or door on hot days. You can also use shade cloth or a white wash to reflect some of the sunlight and reduce the temperature inside the cold frame.

When is the best time to plant in a cold frame?

The best time to plant in a cold frame depends on your location and the type of plants you want to grow. In general, you can start planting in a cold frame as early as February or March and continue planting throughout the spring and summer months. You can also use a cold frame to extend the growing season into the fall and winter. Usually, a cold frame can add two weeks or more to either end of the growing season.

How much warmer is a cold frame at night compared to outside temperatures?

A cold frame can be several degrees warmer than the outside temperature at night, depending on the type of material used to cover the frame and the amount of insulation provided. On average, a cold frame can be anywhere from 5 to 10 degrees warmer than the outside temperature at night.