Cold Frame Gardening Tips: With Pictures

Last Updated on August 28, 2023 by Amit

A cold frame is a miniature greenhouse, often constructed using simple materials like old windows and wooden structures. It is a protective shield that captures the sun’s warmth and creates a cozy microclimate for plants to thrive in conditions they typically wouldn’t.

This age-old gardening method, used for centuries, has empowered gardeners to defy the seasons, starting seeds early in spring and harvesting crops in the dead of winter.

The beauty of cold frames lies not just in their simplicity but also in their adaptability. Whether you’re an urban gardener with a small balcony or have sprawling garden beds in the countryside, cold frames can be tailored to various scales and needs.

In this blog, we’ll delve deep into the art and science of cold frame gardening. From understanding its basic structure to mastering the tricks of temperature management, plant selection, and beyond, prepare to embark on a journey that might revolutionize your green thumb experiences.

Benefits of Using Cold Frames in Gardening

Extended Growing Season: Cold frames allow gardeners to get a head start in the spring by sowing seeds before the last frost and prolonging the growing season into the fall and winter. This means more months of fresh produce!

Protection from Elements: They shield against harsh weather conditions such as frost, heavy rain, and wind, ensuring that young plants and seedlings aren’t damaged.

Microclimate Creation: The contained environment of a cold frame can be several degrees warmer than the external environment. This microclimate is perfect for germination and growth, especially for plants that prefer a bit more warmth.

Pest Protection: While they’re not entirely pest-proof, cold frames can help deter certain pests like birds, rodents, and some insects from feasting on your plants.

Enhanced Seed Germination: The warmer, stable environment within the cold frame can lead to higher germination rates for seeds, giving them a strong start in life.

Water Conservation: Cold frames can help conserve moisture as the enclosed environment reduces the evaporation rate. This can be particularly beneficial in regions where water is scarce.

Versatility: Cold frames can be made from various materials, from repurposed windows to polycarbonate sheets, making them adaptable to different budgets and garden sizes. Depending on a gardener’s needs, they can also be portable or fixed.

Organic Growth Boost: Gardeners who aim for organic growth will find cold frames beneficial. The controlled environment means fewer pests, which reduces the need for chemical pesticides.

Acclimatization Assistance: Before transplanting outdoors, seedlings can be “hardened off” in a cold frame. This process gradually exposes them to the outside conditions, ensuring a smoother transition and reducing transplant shock.

Cost-effective: Compared to greenhouses, which can be expensive to set up and maintain, cold frames offer a budget-friendly alternative for those who enjoy some of the benefits of a controlled growing environment without the hefty price tag.

Space-saving: Cold frames offer an excellent solution for those with limited garden space. They can fit into small corners or even on balconies, ensuring that even city dwellers can enjoy fresh, home-grown produce.

Components of a Cold Frame

Here’s a closer look at the three main components of a cold frame:

Top (Often Transparent)

Material Choices: Common materials for the top include old windows, clear plastic sheets, and polycarbonate panels.

Function: The transparent or translucent top allows sunlight to penetrate, turning the cold frame into a solar collector. It warms the interior and promotes plant growth.

Ventilation: The top can be propped open during warmer days to prevent overheating and ensure adequate air circulation, vital for plant health.

Sides

Material Choices: The sides can be wood, brick, concrete, straw bales, or stacked stones.

Function: The sides provide structural integrity to the cold frame and offer insulation. They shield the plants from cold winds and help retain the heat captured during the day.

Design Considerations: The back (north-facing side) is often taller than the front (south-facing side). This slant aids in maximizing sunlight capture and ensuring that water doesn’t accumulate on the top.

Bottom (Soil or Another Base)

Direct Soil Contact: Most cold frames are placed directly on the ground, allowing plants to grow in the garden soil. This setup offers natural warmth from the earth and ensures plants have ample room for root growth.

Alternative Bases: In some cases, a solid base like wood or concrete might be used, primarily if the cold frame is used for hardening off plants in containers or for starting seedlings in trays. It’s essential to ensure proper drainage if using a solid base.

Drainage: Regardless of the base used, drainage is vital. If the cold frame is placed in an area prone to waterlogging, adding gravel or sand beneath the soil can aid drainage.

Understanding these components and their interplay will guide you in choosing the right cold frame for purchase or designing one tailored to your garden’s needs.

How Cold Frames Work: Trapping Solar Energy to Create a Microclimate

Cold frames are a marvel of simplicity, harnessing the sun’s natural energy to create a unique environment for plants. Here’s a breakdown of how this ingenious system operates:

Solar Collection: The transparent or translucent top of a cold frame allows sunlight to enter. This sunlight, even from the low winter sun, contains energy in the form of heat.

Heat Retention: Once the sunlight penetrates the cold frame, it heats the air, soil, and any objects inside. The materials used for the sides and the base, whether wood, brick or another insulator, help retain this heat.

As the soil or base warms up, it acts as a heat reservoir, slowly releasing warmth into the cold frame’s interior as temperatures drop outside.

Protection from External Elements: The solid sides of the cold frame provide a barrier against cold winds, rain, and frost. By shielding plants from these external elements, the cold frame reduces the loss of trapped heat.

Creation of a Microclimate: All these factors combined lead to the formation of a microclimate inside the cold frame. This microclimate can be several degrees warmer than the external environment, especially when the difference is most pronounced at night.

Additionally, the enclosed space raises humidity levels, which can benefit seed germination and plant growth.

Ventilation and Temperature Regulation: On sunny days, especially as the seasons transition, the interior of a cold frame can get quite warm. Gardeners can prop open the top to prevent overheating and provide fresh air. This process is crucial for temperature regulation and ensures plants don’t suffer from excessive heat.

Adapting to Daily Cycles: Cold frames leverage the daily solar cycle. During the day, they capture and store heat. At night, when temperatures plunge, they release this stored heat, maintaining a relatively stable and warm environment for the plants inside.

Choosing the Right Location for Your Cold Frame

Selecting the ideal spot for your cold frame can differentiate between a bountiful harvest and mediocre results. Location influences the amount of sunlight the cold frame receives, its drainage, and how well it protects plants from adverse weather conditions.

Here are vital considerations to ensure you choose the best location:

Sunlight Exposure

South-Facing: Cold frames should ideally be positioned so they face south (in the Northern Hemisphere) to maximize sunlight exposure. In the Southern Hemisphere, a north-facing orientation is preferable.

Full Sun: Choose a spot that receives at least 6 hours of direct sunlight daily. The more sun, the warmer the cold frame will get.

Wind Protection

Natural Barriers: It’s advantageous to place the cold frame near a hedge, wall, or building that can act as a windbreak, especially for north and west prevailing winds, which tend to be colder.

Avoid Wind Tunnels: Be wary of areas between buildings where wind can funnel and intensify.

Good Drainage

Elevated Ground: Position the cold frame on slightly elevated ground to encourage water runoff and prevent waterlogging.

Soil Quality: Loamy or sandy soil offers better drainage compared to clayey soil. If the drainage is poor, consider adding a layer of gravel beneath the frame’s soil.

Accessibility

Regular Checks: You’ll need to regularly monitor the plants, temperature, and moisture levels inside the cold frame. Therefore, choose a location that is easily accessible to you.

Water Source: Positioning the cold frame near a water source can make watering more convenient.

Avoid Overhead Hazards

Falling Debris: Keep the cold frame away from locations where it might be at risk from falling branches, icicles, or other debris.

Shade: While protection from elements is good, avoid placing the cold frame directly under large trees or structures that cast shadows for most of the day.

Consider the Angle

The back of the cold frame (typically north-facing in the Northern Hemisphere) should be slightly higher than the front. This slight angle maximizes sunlight capture and ensures that rainwater runs off efficiently.

Room for Expansion

If you’re considering adding more cold frames in the future or other garden structures, ensure adequate space for expansion without crowding.

Cold Frame Materials: Exploring Options and Their Benefits

When constructing or purchasing a cold frame, the materials you select can significantly impact its durability, insulation properties, and overall effectiveness.

Let’s delve into the common materials used for cold frames and their respective pros and cons:

Transparent Top Materials

a. Old Windows:

Pros: Reusing old windows is eco-friendly, cost-effective, and can give a rustic look to the garden.

Cons: Old windows can be heavy, and the glass can be fragile. They may also lack UV protection, which some plants might benefit from.

b. Polycarbonate Panels:

Pros: Lightweight, durable, and offers good insulation. Twin-wall polycarbonate panels have excellent insulative properties.

Cons: More expensive than other options and can become discolored over time.

c. Clear Plastic Sheeting:

Pros: Cheap, lightweight, and easy to replace.

Cons: Less durable, can deteriorate quickly under UV rays, and might provide less insulation than other materials.

Side Materials

a. Wood:

Pros: Natural look, sturdy, and provides good insulation. Cedar and redwood are remarkably durable and resistant to rot.

Cons: Can be prone to decay if not appropriately treated. It may require regular maintenance, like staining or painting.

b. Bricks or Cinder Blocks:

Pros: Extremely durable and provides excellent insulation. They also retain heat well, releasing it slowly.

Cons: Heavier, more permanent, and can be more labor-intensive to set up.

c. Straw Bales:

Pros: Excellent insulation and easy to set up. Ideal for temporary cold frames.

Cons: Decomposes over time and can attract pests.

d. Corrugated Metal or Aluminum:

Pros: Durable, rust-resistant, and lightweight.

Cons: It provides less insulation than some other materials.

Base Materials (if not using direct soil)

a. Gravel:

Pros: Improves drainage and adds a layer of insulation.

Cons: Weeds may sprout if a weed barrier isn’t used.

b. Pavers or Concrete Slabs:

Pros: Durable and provides a solid, flat base.

Cons: Doesn’t offer the insulation of soil and may require additional drainage solutions.

c. Wooden Planks:

Pros: Raises the cold frame off the ground, making it more accessible.

Cons: Can rot over time if not treated.

Temperature Management Inside the Cold Frame

The primary purpose of a cold frame is to create a favorable microclimate for plants during colder periods. However, even during these cooler times, the sun’s energy can rapidly increase temperatures.

Overheating can be as detrimental as freezing temperatures, so actively managing the internal temperature is crucial.

Here’s a guide to ensure your plants remain in an optimal environment:

Monitoring:

Thermometer: Always have a thermometer inside your cold frame. It helps you keep a constant check on the internal temperature.

Daily Checks: Temperature fluctuations can be common, especially in transitional seasons, so check daily, ideally in the morning and late afternoon.

Ventilation:

Manual Venting: On sunny days, prop open the cold frame lid slightly to allow excess heat to escape. The degree to which you open it will depend on the external temperature.

Automatic Vent Openers: These devices automatically open the cold frame’s lid when a specific temperature is reached. They utilize a wax cylinder that expands with heat, pushing the cover open, and contracts in the cold, closing it.

Shading:

Shade Cloth: On exceptionally sunny days, especially as the seasons transition, a shade cloth can be draped over the cold frame to reduce the intensity of sunlight and, thus, the heat.

White Wash: Some gardeners paint the cold frame’s transparent top with a diluted whitewash during peak summer, reflecting some sunlight. It can be washed off when full transparency is desired again.

Insulation:

Bubble Wrap: Lining the inner sides of the cold frame with bubble wrap can provide extra insulation on freezing nights.

Straw or Hay Bales: Placing these around the exterior of the cold frame can help insulate and protect from cold winds.

Old Blankets or Rugs: These can be draped over the cold frame during frosty nights and removed during the day.

Water Barrels:

Heat Absorption: Placing black water barrels or containers inside the cold frame can be effective. They absorb heat during the day and radiate it out during the night, helping maintain a consistent temperature.

Soil Considerations:

Dark Soil Absorbs Heat: Darker soil or compost can help absorb more sunlight and retain warmth during colder periods.

Mulching: Mulch acts as an insulator. Applying a thick layer of organic mulch, like straw or leaves, around plants can help regulate soil temperature.

Cold Snaps and Freezing Temperatures:

Heating Cables: For gardeners in freezing climates, soil heating cables can be installed below the surface to provide steady, gentle heat.

Candle or Lamp: A small candle or lamp can give off enough heat to raise the inside temperature a few degrees, preventing frost damage. However, be cautious and ensure there’s no fire hazard.

Plant Selection and Timing for Cold Frames

Cold frames can extend your gardening season by providing a more stable and warmer microclimate than the surrounding environment. However, for success, it’s vital to choose the right plants and understand the optimal timing for planting.

Here’s a guide to help you make informed decisions:

1. Plant Selection:

Cool-Season Crops: These are ideal for cold frames as they tolerate frost and cooler temperatures. Some examples include:

Leafy Greens: Lettuce, spinach, kale, and Swiss chard thrive in cold frames.

Root Vegetables: Radishes, carrots, and beets can benefit from an early start in a cold frame.

Herbs: Cilantro, parsley, and chervil are suitable cool-season herbs.

Transplants: Cold frames are excellent for starting seedlings early in the season, which can later be transplanted into the main garden. This includes both cool and warm-season crops.

Winter-Hardy Plants: Some plants can survive even the coldest months in a cold frame, such as mache (corn salad), some kale, and winter lettuce.

2. Timing:

Spring:

Early Start: Begin sowing cool-season crops in the cold frame several weeks before the last expected frost date. This gives them a head start and ensures an early harvest.

Hardening Off: Before transplanting seedlings started indoors to the main garden, move them to the cold frame to acclimate to outdoor conditions gradually.

Summer:

Succession Planting: After harvesting your spring crops, replant with another round for a continuous supply.

Protection from Excessive Heat: Be cautious during peak summer; cold frames can become too hot. Consider using them to harden off plants for autumn planting during this period or leave them open for regular summer crops.

Autumn:

Extended Harvest: Plant late-season cool crops, allowing you to harvest them well into fall and winter.

Overwintering Crops: Some crops can be planted in late summer or early fall and left to grow slowly over winter for an early spring harvest.

Winter:

Growth Pause: In extremely cold areas, plants might stop growing during the coldest months but will remain alive. They’ll resume growth as daylight increases, giving you an early spring harvest.

Microgreens and Sprouts: If you want fresh greens in winter, consider growing microgreens and sprouts in your cold frame.

3. Tips:

Know Your Zone: Understanding your USDA hardiness zone will help determine what plants can thrive at different times of the year.

Monitor Soil Temperature: This is just as crucial as air temperature. Some seeds have optimal soil temperature ranges for germination.

Rotate Crops: If you use your cold frame year-round, rotate crops to prevent soil-borne diseases and maintain soil health.

Soil and Watering Considerations in Cold Frame Gardening

Ensuring successful cold frame gardening is not just about managing temperature or choosing the right plants; the soil’s quality and correct watering practices play pivotal roles.

Here’s what you need to know:

1. Soil Considerations:

Soil Composition: The ideal soil mixture for cold frames is a blend of garden soil, compost, and a bit of coarse sand for drainage. This combination ensures a nutrient-rich medium that retains moisture without becoming waterlogged.

Drainage: Good drainage is paramount. Stagnant water can lead to root rot and other plant diseases. Ensure your cold frame’s base has a slight incline, or add a layer of gravel beneath the soil to enhance drainage.

Soil Depth: Aim for at least 12 inches of soil depth to accommodate a variety of crops, especially if you plan to grow root vegetables.

Soil Temperature: Remember that some seeds require specific soil temperatures to germinate. Even if the air in the cold frame feels warm, the soil might still be too cold. A soil thermometer can be helpful.

Refresh the Soil: If you’re using your cold frame throughout the year, it’s a good idea to refresh the soil at least once a year by adding new compost or organic matter.

2. Watering Considerations:

Water Source: Having a water source close to your cold frame will make the task easier and ensure regular watering.

Morning Watering: It’s best to water plants in the morning. This gives them ample time to absorb it before the colder evening temperatures. Avoid watering in the evening, as cold temperatures and wet soil can stress plants.

Monitor Moisture Levels: Overwatering is a common mistake in cold frame gardening because the enclosed space reduces evaporation. Check the soil’s moisture a few inches down. If it feels damp, wait another day before watering.

Watering Methods:

Hand Watering: This is the most common method and gives you control over the amount of water each plant receives.

Soaker Hoses: If you have a larger cold frame, consider using soaker hoses, which deliver water directly to the roots and minimize evaporation.

Watering Cans with Long Spouts: These are ideal for targeting water at the base of the plants, keeping foliage dry, which can help prevent fungal diseases.

Humidity: Cold frames can become quite humid due to the trapped moisture. Open the lid slightly on sunny days to allow ventilation and reduce excessive humidity.

Rainfall: Remember that when the cold frame lid is closed, rain can’t penetrate it. So, even if it’s raining outside, you might still need to water the plants inside.

Maintenance and Pest Management in Cold Frame Gardening

Even with the controlled environment a cold frame provides, it’s challenging. Regular maintenance and proactive pest management can ensure your cold frame remains an optimal space for plant growth.

Here’s what you need to consider:

1. Maintenance:

Cleaning: Over time, the transparent top of your cold frame can accumulate dirt, reducing the amount of sunlight reaching your plants. Regularly clean the top with water and mild detergent to keep it clear. If it’s made of plastic, avoid abrasive materials that could scratch it.

Seal Leaks: Check for cracks or gaps that might let in cold drafts and repair them immediately. This is especially important as seasons transition and temperatures drop.

Hinges and Supports: Regularly inspect and oil the hinges of your cold frame to ensure they operate smoothly. If you’re using props or supports to keep the lid open, ensure they’re sturdy and in good condition.

Refreshing Soil: If you’re planting in your cold frame year-round, consider refreshing or amending the soil annually with compost or organic matter to maintain soil fertility.

2. Pest Management:

Regular Inspection: Check plants regularly for signs of pests or diseases. The confined space of a cold frame can mean issues spread quickly.

Physical Barriers: If you’re dealing with larger pests like rodents or birds, consider adding a layer of hardware cloth or mesh under the soil and around the sides.

Natural Predators: Encourage beneficial insects like ladybugs, lacewings, and predatory mites. They can naturally keep pest populations like aphids and spider mites in check.

Diatomaceous Earth: This is a natural insect killer and can be sprinkled on the soil’s surface. It’s effective against crawling insects like ants and slugs.

Neem Oil: A natural pesticide, neem oil can be used as a preventive measure against a range of pests. However, use it sparingly and preferably when the cold frame is open to avoid harming beneficial insects.

Ventilation: Regularly ventilating your cold frame reduces humidity, making it less hospitable for pests like fungi gnats and diseases like mold.

Crop Rotation: If you’re planting in the cold frame continuously, try not to repeatedly plant the same crop in the same spot. Rotating crops can reduce the buildup of crop-specific pests and diseases.

Healthy Soil: Healthy soil often equates to healthy plants. Plants growing in rich, well-balanced soil are generally more resistant to pests and diseases.

Advanced Tips and Tricks for Cold Frame Gardening

While the basics of cold frame gardening can offer excellent results, advanced gardeners often seek ways to optimize their setups further.

Here are some expert tips and tricks to elevate your cold frame gardening experience:

1. Dual-Purpose Lids:

Hinged Double Lids: Consider a design with two lids instead of one. On warmer days, you can open just one side for ventilation, ensuring optimal temperature.

Convertible Tops: Use a lid with a transparent section for cold months and a shade cloth section for warmer months. This way, you can adjust based on the weather without changing the entire lid.

2. Automated Systems:

Solar-Powered Fans: Integrate small solar-powered fans for increased ventilation during hotter days, ensuring consistent air circulation.

Drip Irrigation: Implementing a drip irrigation system ensures plants get a consistent water supply without the risk of overwatering.

3. Deep Cold Frames:

Trench Gardening: Digging a trench about a foot deep and placing your cold frame over it allows for an even more stable thermal environment, as the ground remains at a relatively consistent temperature year-round.

4. Mobile Cold Frames:

On Wheels: Design your cold frame with wheels. This way, you can move it around the garden, utilizing it where needed and following the sun during transitional seasons.

5. Reflective Surfaces:

Maximize Sunlight: Place reflective materials or surfaces (like whiteboards or aluminum foil) on the sides facing away from the sun to redirect sunlight back into the cold frame, especially during shorter winter days.

6. Multi-layer Insulation:

Double Glazing: Much like energy-efficient windows, a double-glazed cold frame lid can provide an extra layer of insulation.

Bubble Wrap: In particularly cold climates, line the insides of your cold frame with bubble wrap to add another layer of insulation.

7. Companion Planting:

Beneficial Partners: Plant crops that benefit each other within the cold frame. For example, radishes can be grown with lettuce. Radishes grow quickly, marking the row, and by the time they’re harvested, the slower-growing lettuce needs the space.

8. Succession Planting Strategy:

Continuous Harvest: Plan your plantings so that as one crop is harvested, another is ready to take its place. This ensures a constant supply of produce.

9. Intercropping:

Space Utilization: Grow fast-maturing crops like radishes or lettuce between slower-growing ones like broccoli. By the time the slow growers need more space, the fast growers have been harvested.

10. Soil Solarization:

Pest Control: During the hottest part of the year, leave your cold frame closed and empty for a week or two. The heat will kill many soil pests, diseases, and weed seeds, preparing it for the next planting cycle.

Final Thoughts

Cold frame gardening, an age-old method, has grown in popularity among gardeners of all levels. Cold frames allow garden enthusiasts to defy traditional growing seasons, obtain fresh produce nearly year-round, and get a head start on spring plantings by creating a protective microclimate for plants.

From the basics of choosing the right location and materials to advanced techniques like mobile designs and automated systems, cold frames offer many options tailored to beginners and seasoned green thumbs.

The beauty of cold frame gardening lies not just in its versatility but also in the way it encourages experimentation. Every garden, region, and climate will present unique challenges and rewards.

By understanding and adapting to these variables, gardeners can unlock the full potential of their cold frames.

FAQs on Cold Frame Gardening Tips

Q: What crops grow best in a cold frame?

A: Leafy greens like lettuce, kale, and spinach thrive in cold frames. Additionally, root vegetables like carrots and radishes, as well as brassicas like broccoli and cauliflower, can benefit from the protection of a cold frame, especially during their early stages.

Q: Is a cold frame better than a greenhouse?

A: It depends on the purpose. Cold frames are smaller, cheaper, and suitable for protecting plants during transitional seasons.

Greenhouses are larger structures designed for year-round cultivation and can accommodate various plants. The choice between them depends on space, budget, and gardening goals.

Q: How long can you grow in a cold frame?

A: With the proper management, you can use a cold frame to extend the growing season by several weeks in the spring and fall. In milder climates, growing certain crops throughout the winter is possible.

Q: What is the best use of a cold frame?

A: The primary use of a cold frame is to protect plants from harsh weather conditions, to extend the growing season, and to harden off seedlings before transplanting them outdoors.

They’re excellent for early starts in spring and for growing cold-hardy crops in the fall and winter.

Q: How do you keep a cold frame warm at night?

A: To keep a cold frame warm at night, ensure it’s well-insulated and consider using thermal mass objects, like water-filled containers or bricks, which absorb heat during the day and release it at night.

Covering the cold frame with blankets or burlap can also provide extra insulation during freezing nights.

Q: Can I grow herbs in a cold frame?

A: Absolutely! Many herbs, such as parsley, cilantro, and chives, can thrive in a cold frame, especially during cooler months when they might not survive outside.

Q: Does a cold frame need to be in the sun?

A: Ideally, yes. A cold frame should be positioned in a location that receives ample sunlight, preferably south-facing in the Northern Hemisphere. The transparent lid captures solar energy, creating a warmer microclimate inside.

Q: Do you need to water in a cold frame?

A: Yes, plants in a cold frame still require watering, though perhaps less frequently than outside due to reduced evaporation. It is essential to monitor the soil moisture and ensure it remains consistently damp but not soggy.

Q: What is the best angle for a cold frame?

A: If you’re constructing a sloping cold frame, aiming for an angle of 30-40 degrees towards the sun (usually south in the Northern Hemisphere) is ideal. This orientation captures maximum sunlight during the cooler months.