Grow Greens All Winter Using a Cold Frame

By Bethany Hayes

Nothing makes me sadder than when the garden season comes to an end, but using a cold frame allows gardeners the opportunity to extend their growing season. For those who live in regions with cold periods, we need season extenders to make use of each week.

Believe it or not, you can grow greens well into the fall and winter with cold frames. It gives you a simple way to continue eating fresh greens and even some brassicas as the temperatures dip down. 

Ready to give it a try? Let’s take a look at what you should know. 

What is a Cold Frame?

The name suggests what this is; it’s an outdoor frame covered with a transparent or clear cover, typically glass or plastic, that protects your plants throughout the cold winter months while also letting sunlight inside. 

You don’t heat cold frames as you might heat greenhouses; they’re unheated, so all of their power comes from solar energy. Solar power comes and stores inside of the structure and soil throughout the day. The frames shelter your plants from the snow, ice, and winter winds, warming up the oil even when the temperatures outside aren’t as warm. 

This is an excellent tool for gardeners, giving your plants natural sunlight and extra warmth when they won’t receive that from outside elements. However, if you live in a USDA hardiness zone below 6, you will need a more robust, hardier version for your winter greens and crops. 

Materials Needed to Make a Cold Frame 

The fantastic thing about building a DIY cold frame is that you can use whatever materials you want or have on hand. You can be as creative a possible or buy all of the materials new. 

Here are some examples.

• Top of the Cold Frame

The top of the frame is where you’ll put your light-permeable cover; it will be used to open and close. You’ll have to create a structure to hold the material that you select. A few examples include:

• Glass
• Old Windows
• Plexiglass
• Greenhouse Plastic

It’s best if the top is slightly angled toward the sun to absorb as much sunlight as possible. You can either cut slanted sides in the wood or mound soil underneath it at an angle to make the front lower than the back, which is where the hinges will be located. 

• The Sides

Most people use wood to create the sides; you need to create a supportive structure to hold up the cold frame’s cover. Some people use wood; it’s the most substantial option, and it will hold up the edge of the top. 

Another option is to use straw bales. They’re thick and insulating, inexpensive, fully biodegradable, and easy to put together. However, they won’t last for years, so if you want something permanent, straw bales won’t be the best choice. 

• The Bottom

You don’t need to add a bottom to your cold frame; you can leave it open and fill your frame with soil. If you need to create a base for your cold frame, you’ll need to make sure it allows water to drain thoroughly. 

Examples of DIY Cold Frame Plans

If you’re looking for plans to build your own at home, here are some DIY ideas.

• A Simple Cold Frame
• PVC Pipe Frame
• DIY Cold Frame Tent
• An Amish Cold Frame
• Easy Polycarbonate DIY Frame
• An Intermediate Frame Plan

What Vegetables Grow Well in a Cold Frame?

When you pick the plants that you want to grow, remember that inside of the cold frames will only be slightly warmer than outside. They are best used in the winter with frost-tolerant crops during the winter, so look for these hardy crops. 

• Lettuce
• Spinach
• Arugula
• Kale
• Broccoli
• Cabbage
• Swiss Chard
• Radishes
• Cauliflower
• Scallions
• Beets
• Chinese Cabbage
• Mustard Greens

5 Tips for Growing Greens in the Cold Frame

1. Select the Best Location for Your Cold Frame

The first thing that you need to do is to find the best location to build it. The best place is to find a south-facing spot with early morning sunlight; this sunlight is the strongest, and it will heat your cold frames enough for the entire day.

Ensure that you don’t put them on the north side of the house, near a building, or a tall tree. These placements won’t provide enough sunlight.

2. The Materials You Select Do Matter

While you can be as creative as you want while creating this, the materials you select do matter. The most common are wood, polycarbonate, straw bales, and bricks. 

Many gardeners note that the selection of materials does lend a hand to whether or not your cold frame will be successful. 

For example, you can find pre-made options at garden centers created with polycarbonate sides and tops. These are great for spring and fall, but they won’t provide enough protection to grow greens all winter. 

3. Ventilation Matters – Majorly 

This is where so many gardeners flop – they fail to add ventilation when they create their frames. In the fall and spring, temperatures can fluctuate wildly. One day, it’s 40℉ with clouds and rain, and the next day it’s 75℉ with an abundance of sunshine. 

It’s essential to prop up the lid during warm weather, but you can buy automatic vent openers that will open the top when the temperature inside reaches a specified degree. 

If you don’t add plenty of ventilation, you can kill your plants – essentially frying them to death. That’s not the only problem; it also can heat up your fall and winter crops too high, which won’t put them in ideal growing conditions. 

4. Don’t Block Your Tops

Picking your location is vital, and if you’re building in the late fall or early spring, your trees might not be at full bloom. I made this mistake, building a bed too close to a massive mulberry tree. In full bloom, it casts way too much shade. The same thing applies to frames. 

In the winter, you’ll want to brush off the snow regularly to prevent ice build-up. Snow also can block sunlight, preventing your plants from growing. 

5. Paint or Use Foil 

Here is another simple tip. You want to boost the light and heat retention, so a simple idea is to paint the inside of the frame’s walls a nice white or line them with aluminum foil. Another simple trick is to add a few black painted one-gallon water jugs. When they’re filled with water, they’ll absorb heat during the day and release it throughout the night, increasing the frames’ temperature. 

6. Add Extra Protection

You should install a thermometer into the frame to monitor any temperature fluctuations. You need to know how hot or cold it is inside of the frame. 

It’s best to build the frame’s back next to a wall to provide extra protection against northerly winds. Keep old blankets or hay on standby; you can add it over the top for extra insulation on freezing nights. 

Other Ways That You Can Use a Cold Frame 

You know that a cold frame can be used to extend the growing season or extend the harvesting season, but they can do so much more than that. Here are some reasons that you might want to add a cold frame to your garden. 

1. Start Your Seedlings Earlier

When you have a cold frame, the soil in it will be warmer than the soil in your typical garden beds. That warmth allows you to sow early vegetables sooner than average, such as spinach, peas, or radishes. 

Not only is the ground warmer, but it keeps the seeds themselves warmer, so it helps them germinate faster, giving you a head start. 

That doesn’t mean you should start warm-season vegetables in them. Plants such as tomatoes and peppers need high temperatures, so it’s still best to start them outside if you live in a colder region. 

2. Harden Off Your Seedling

When you start your seeds inside, the process of bringing them outside is called hardening off. Typically, you do this by placing them in a sheltered spot outside gradually for more extended periods each day. The process can take up to two weeks, but it can be a pain in the butt.

Each day, you have to think about how long they’ve been outside and move all of your seedlings inside and outside. If you have dozens or hundreds of seedlings, that can be a serious chore. 

Moving them to a cold frame makes the process a lot easier. Just move your seedlings into the cold frame and open the lid for more extended periods each day. You don’t have to worry about moving the seedlings in and out each day. 

Truth be told, I’ve broken several seedlings this way as well! 

3. Overwinter Plants

Some plants can live their entire lives inside a cold frame. You can sow them in late summer, keeping them throughout the winter. Even very hardy plants can appreciate being covered throughout the summer, and without a snow cover, you can find the plants to harvest. 

Final Thoughts

If you want to grow green all winter, using a cold frame is a genius idea. These little frames can help hold in the solar energy, warming up the soil, allowing you to grow veggies earlier in the spring and later in the fall. You can grow greens well into the winter by the use of these simple frames. 

Learn More About Cold Frames

https://extension2.missouri.edu/g6965

https://www.hort.purdue.edu/hort/ext/Pubs/HO/HO_053.pdf