Cold Frame Gardening (Easy Tips to Build, Grow, and Harvest Year-Round!)

A cold frame is a simple, low-cost way to keep growing food even when the weather turns cold. It acts like a small greenhouse, trapping warmth and protecting plants from frost, wind, and snow.

Whether you want to enjoy fresh greens in winter, start seedlings early in spring, or extend your harvest into late fall, a cold frame can make it possible.

In this article, you’ll learn how to build a cold frame, choose the right materials, manage heat and light, pick the best crops, and keep your plants healthy year-round.

Why Grow in a Cold Frame?

Cold frames give gardeners a simple and affordable way to grow more food for a longer part of the year.

Here are the main reasons why many gardeners rely on cold frames.

Extend the Growing Season

A cold frame lets you start planting earlier in spring and keep harvesting later into fall. In many areas, it’s even possible to grow hardy greens and root crops right through the winter.

Protect Plants from Harsh Weather

The clear cover shields crops from frost, wind, heavy rain, and snow. This creates a safer and more stable environment for your plants, helping them grow better in difficult weather.

Grow in Small Spaces

Cold frames are a good option for gardeners with limited space. They work well in small yards, patios, or even urban gardens, giving you fresh food without needing a large plot.

Save Money

You can build a cold frame cheaply, especially if you use reclaimed materials like old windows, scrap wood, or straw bales. This makes it a budget-friendly way to extend your harvest.

Create a Warmer Microclimate

A cold frame can make your garden feel like it’s one or two USDA zones warmer. This means you can grow crops that might not normally survive in your area.

Easy to Care For

Once set up, a cold frame needs little maintenance beyond venting, occasional watering, and harvesting.

A Space to Learn and Experiment

Cold frames give you the chance to try new crops and growing methods. You can also use them to harden off seedlings, grow cuttings, or protect tender plants through winter.

Picking the Best Spot for Your Cold Frame

Choosing the right location is important for getting the most out of your cold frame. A good spot will give your plants plenty of light and some extra protection from harsh weather.

Face It Toward the Sun

The best direction for a cold frame is usually south because it gets the most sunlight during the day.

If you want to avoid too much heat in the afternoon, you can also choose a spot that faces east or southeast. This way, the plants still get morning sun but stay cooler later in the day.

Use Natural Shelters

Placing your cold frame next to a house, shed, garage, or deck can offer extra warmth and protection from cold winds. These structures can act like a shield and help hold onto heat, especially during cold nights.

Think About Slope and Drainage

If possible, set the cold frame on a spot with a slight slope. This helps with water drainage and can also improve sun exposure if the slope faces the right direction.

Easy Access Matters

Pick a spot where you can easily reach the cold frame for planting, watering, venting, and harvesting. Convenience will make it easier to care for your plants throughout the seasons.

Easy Ways to Build a Cold Frame

You don’t need fancy tools or expensive materials to build a cold frame. Many gardeners make strong, useful cold frames from items they already have or can get cheaply.

Repurpose Old Windows or Doors

One of the easiest ways to build a cold frame is to use old windows or doors. These materials are often free or inexpensive and provide a perfect clear lid that lets sunlight in.

Simply create a wooden frame using scrap wood or cinder blocks, and then attach the window or door as the lid. This option is great for those who want a sturdy, low-cost cold frame.

Wooden Box with a Hinged Lid

Another straightforward option is to build a simple wooden box with a hinged lid. Cut four pieces of wood to the desired size for the base and sides, then attach them together to form a box.

For the lid, use clear plastic, old windows, or polycarbonate panels. Make sure the lid is hinged so you can easily open it for ventilation. Adding a slight slope to the lid can help with rain runoff.

Straw Bale Cold Frame

If you're looking for an option that requires no building skills, consider using straw bales. Arrange the bales in a rectangular shape, leaving space in the middle for plants.

Top the bales with a clear plastic sheet or old windows to create a simple, insulated cold frame. The straw bales provide natural insulation, keeping the cold out and the warmth in.

Cinder Block Cold Frame

Cinder blocks are another inexpensive and easy material to use for building a cold frame. Stack the blocks to form a rectangular shape, leaving the top open.

For the lid, use clear plastic, old windows, or polycarbonate panels. The cinder blocks provide some insulation and structure without requiring complex construction.

How to Keep the Cold Out

Keeping the cold out is key to helping your plants grow strong, even in chilly weather. There are simple ways to insulate your cold frame and keep it warm.

Use Straw Bales and Bags of Leaves

Straw bales and bags of leaves are great natural insulators. Piling them around the outside of your cold frame creates a thick barrier that helps block out cold air and prevent heat loss.

Straw, in particular, is excellent at trapping air within its fibers, which helps retain warmth.

You can arrange the straw bales or leaves on the north or windward side of the cold frame to shield it from cold winds.

This method is easy to do and costs very little, especially if you have access to leftover straw or dry leaves.

Bank Soil Against the Sides

A simple and free way to add insulation to your cold frame is to bank soil around the outer edges.

By mounding soil against the walls, you can help keep the cold from seeping in from the sides and provide extra thermal mass.

The earth absorbs heat during the day and slowly releases it at night, helping to stabilize the temperature inside your cold frame.

This technique also helps protect the structure from frost heaving, which can happen when the ground freezes and thaws repeatedly.

Line the Inside for Extra Warmth

If you live in a region with particularly cold winters, you may want to add an extra layer of insulation inside your cold frame.

Lining the interior walls with materials like styrofoam, foam board, or even old carpet can create an extra layer of warmth.

These materials trap heat and prevent it from escaping, especially at night when temperatures drop.

Just be sure to leave some ventilation space to prevent humidity buildup, which can lead to mold and mildew.

Add Extra Covers When Needed

On exceptionally cold nights or cloudy days when the sun isn't warming your cold frame, adding an extra layer of protection can make a huge difference.

You can use an old blanket, quilt, or even a heavy-duty tarp to cover the cold frame. This creates an additional layer of insulation and helps trap heat inside.

Be sure to remove the covers during the day, especially on sunny days, to allow for proper ventilation and prevent overheating.

Create a Microclimate

If you place your cold frame against a wall or structure that absorbs heat during the day (like a greenhouse or brick wall), it can create a warmer microclimate. This can make it feel like you’re gardening in a region one or two zones warmer.

What to Use for the Top (Lid or Cover)

The lid, or cover, is one of the most important parts of a cold frame. It lets sunlight in while keeping the cold out.

Glass or Clear Plastic

Glass is one of the most common materials used for cold frame lids, especially old windows that are easy to repurpose.

It allows plenty of sunlight to reach your plants while providing a sturdy and weather-resistant cover. Glass is also durable, but it can be heavy, and it’s more prone to breaking if not handled carefully.

If you’re looking for a lighter, safer alternative, clear plastic sheets can also do the job. Clear plastic is easier to work with and won’t break as easily as glass, making it ideal for DIY projects.

You can find plastic sheets that are specifically designed for cold frames, but any clear plastic will work, as long as it allows enough light to pass through.

Single-Wall or Double-Wall Polycarbonate

For colder climates, using a more insulating material can make a big difference in keeping your cold frame warm.

Polycarbonate panels—especially double-wall polycarbonate—are an excellent choice for insulation.

These panels trap heat within the two layers of plastic, which helps keep your plants warmer during colder nights.

Single-wall polycarbonate is less expensive but still provides better insulation than glass or standard plastic.

Double-wall polycarbonate is the most efficient for heat retention, making it ideal for areas with very cold winters.

While double-wall polycarbonate tends to be pricier, the extra insulation is worth it if you’re gardening in a harsh climate.

Keep It Simple and Sturdy

Your cold frame lid should be strong enough to withstand weather conditions, including light snow, but not so heavy that it’s difficult to open for ventilation.

Snow can accumulate on top of the lid, so make sure it can handle the weight without bending or breaking. It’s a good idea to brush off the snow regularly to avoid any potential damage.

You also want the lid to be easy to open. Proper ventilation is essential, especially during sunny days when the temperature inside the cold frame can rise quickly.

You can achieve this by either installing a hinged lid or creating a removable cover. The key is to make sure the cover is easy to lift or open, even when it's covered with snow or ice.

Letting Fresh Air In

Venting is important because it stops the cold frame from getting too hot. Even in winter, the sun can warm the inside of the frame quickly.

Without fresh air, plants can overheat or grow too fast, making them weak and more likely to get damaged by cold nights.

How to Vent by Hand

On sunny days, especially when the temperature is above 40°F (4°C), you should prop open the lid a little to let out extra heat. This also brings in fresh air, which plants need to stay healthy.

Using Automatic Vent Openers

If you want less work, you can add an automatic vent opener. This handy tool opens the lid when the inside gets too warm and closes it when it cools down.

Best Plants to Grow in a Cold Frame

Choosing the right crops is the key to success with cold frame gardening. Some plants handle cold weather much better than others.

Category	Plants
Hardy Greens and Herbs	Spinach, mâche (corn salad), claytonia, scallions, arugula, mizuna, parsley, sorrel, mustard greens
Root Vegetables	Carrots, turnips (cold weather makes them sweeter)
European Salad Greens	Frisée endive, radicchio, minutina, ‘Biondissima Trieste' chicory, mâche (very hardy, can be harvested when frozen)

When to Plant

For winter harvests, it’s important to plant early in the fall so the crops can grow to a good size before the days get short and cold. In Maine, for example, planting often starts between mid-July and September, but you should adjust this timing based on your local climate.

Keeping Plants Warm and Bright

Along with venting, you’ll also need to manage heat and light to keep plants growing well.

• Check Temperatures: Use a digital thermometer to monitor the temperature inside the cold frame, so you know when to vent or cover it.
  
• Reflect More Light: Paint the inside walls white or line them with aluminum foil to reflect more light onto your plants.
  
• Use Water Jugs for Extra Heat: Place black-painted one-gallon water jugs inside the cold frame to absorb heat during the day and release it slowly at night.
  
• Snow Can Help or Hurt: A light layer of snow can act as insulation, but heavy, wet snow should be removed to prevent damage to the lid or blocking sunlight.

Extra Heating Tricks

In very cold weather, adding extra heat to your cold frame can help keep your plants safe and thriving. One popular method is using electric roof ice-melting cords inside the cold frame.

These cords are controlled by a thermostat that turns them on when the temperature inside drops below 40°F (4°C), providing just enough warmth to protect your plants without overheating the space.

On especially cold nights or during prolonged freezing weather, layering additional covers, like a blanket, old quilt, or frost cloth, over the lid can help trap more heat and keep the temperature stable.

However, if you’re using electric heating, it’s important to prioritize safety—make sure the cords and connections are designed for outdoor use and are kept away from any water sources to prevent accidents.

These extra heating tricks can make a big difference in ensuring your cold frame provides the warmth and protection your plants need during the harshest winter conditions.

Planting More as You Go (Year-Round Tips)

Cold frames can be used throughout the year, not just in winter. With good planning, you can keep planting and harvesting in every season.

Fall Planting

For winter crops, timing is everything. Plant your winter vegetables like spinach, kale, and mustard greens in mid to late summer or early fall.

This gives them enough time to grow and establish their roots before cold weather slows their progress.

By planting at the right time, you allow these crops to mature slowly during the cooler months, with the cold frame offering some protection from frost.

Spring Seedlings

Cold frames are an excellent tool for starting seedlings early in the spring.

The extra warmth inside a cold frame helps young plants get a head start, allowing them to develop strong root systems before being planted out in the garden.

A cold frame acts as a mini-greenhouse, protecting tender seedlings from unexpected frosts or chilly nights.

Whether you're starting tomatoes, peppers, or herbs, using a cold frame can give your spring garden a strong start and allow you to transplant earlier than you could with outdoor sowing.

Summer Propagation

In the summer months, cold frames can serve as a great tool for propagating new plants. You can use them to grow new plants from leafy cuttings of perennials, herbs, or other plants that root easily.

The warm, humid environment inside the cold frame encourages healthy root growth. To keep the temperature under control during the hotter months, you may want to add a bit of shade, like a light cloth or shade netting, to prevent the frame from overheating.

This gives you the opportunity to grow more plants without taking up valuable space in your main garden.

Overwintering and Bulb Forcing

Cold frames also serve as a fantastic way to overwinter tender plants, such as certain herbs, lettuce, or flowers that would normally be damaged by freezing temperatures.

By placing them inside a cold frame, you protect them from harsh winter weather while still allowing them to get natural sunlight. In addition, cold frames are perfect for forcing bulbs to bloom early.

By planting bulbs like crocuses, hyacinths, and daffodils in the fall, you can create a cozy environment inside the cold frame to encourage them to bloom in early spring—offering a burst of color and fragrance during the colder months.

Sowing New Crops in Winter

Even in the winter, cold frames can be used to grow certain crops. When space opens up in your cold frame, consider sowing fast-growing, hardy greens like arugula, mâche, spinach, claytonia, or radishes.

While these crops will grow slowly at first, they’ll take off as the days start getting longer and warmer in late winter or early spring.

The cold frame offers enough protection from the elements to give these crops a head start, meaning you’ll be able to harvest fresh, homegrown greens when other gardens are still dormant.

Simple Maintenance Jobs

Cold frames are easy to care for, but a few simple tasks will help keep your plants healthy and growing well.

1. Daily Venting

Check the temperature inside the cold frame each day, especially when the sun is out. Open the lid a little if it gets too warm. If you have an automatic vent opener, this job becomes even easier.

2. Snow and Debris Removal

In winter, brush off snow and fallen leaves from the top of the cold frame. This makes sure enough light can reach your plants. A sturdy push broom works well for this.

3. Check Insulation and Covers

From time to time, inspect the frame’s insulation and lid. Replace or adjust any parts that are damaged or worn out.

4. Monitor Plant Health

Look at your plants regularly to catch any problems early, like pests or diseases. Healthy plants are better able to handle cold temperatures.

Maximize your harvest year-round by using a cold frame to grow fresh food, even in the colder months!

Cold frame gardening is a simple and rewarding way to grow fresh food all year.

By choosing the right spot, building with sturdy or recycled materials, managing heat and light, and picking the best crops, you can enjoy a steady harvest even in the colder months.

Whether you’re growing hardy greens through winter, starting seedlings early in spring, or protecting tender plants, a cold frame can help you make the most of every season.

With just a little care and planning, your cold frame can keep producing food while saving time and money.

Frequently Asked Questions (FAQs)

Got questions about cold frame gardening? Here are some quick answers to help you get started and make the most of your cold frame, no matter the season.

1. What’s the easiest material to build with?

Scrap wood and old windows are some of the easiest and cheapest materials. Straw bales and cinder blocks also work well.

2. How do I stop my cold frame from getting too hot?

Open the lid on sunny days to let out extra heat. You can also install an automatic vent opener to handle this for you.

3. What plants are best for winter growing?

Spinach, mâche, claytonia, scallions, carrots, and hardy greens like mustard and mizuna do very well in winter cold frames.

4. When should I plant for winter harvests?

Most winter crops should be planted in mid to late summer or early fall, depending on your local climate.

5. Can I use a cold frame in summer too?

Yes, cold frames can be used in summer for starting seedlings, growing cuttings, or protecting plants from heavy rain.