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4 ways for using coldframes in your garden

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4 ways for using coldframes in your garden

4 ways for using coldframes in your garden

Hey country friends, today I thought I will review a couple of options for using coldframes in your garden.


What are coldframes?

If you are like me and would like to extend your gardening season to end with the season’s first hard frost, then you will need a cold frame. This simple bottomless box with a removable glass or plastic lid protects plants inside from excessively low temperatures, wind, snow, and rain while creating a microclimate that is a zone+ warmer than your garden! I’m located in Eastern Ontario ‘North of 7’ as the local farmers like to call it, and we get frost around November.  A cold frame in my area of Eastern Ontario provides me more Vancouver like temperatures for my garden,  and I am rewarded with vegetables all winter long!

First things first; what are cold-frames and what is their use?

A cold-frame is simply a structure to keep the sun’s solar energy in an insulated space, and create a micro-climate within your garden.

It is one of the oldest, universal  practices to extend the growing season.  If you want fresh greens in February, or perhaps wish to have flowers well past frost, cold frames are the key. Also, think spring – start seeds early to get a jump on the growing season and sow them into your coldframes.

Which coldframes are right for me?

Now that you know what coldframes are, you are most likely wondering how do you go about purchasing or building these structures?

Take the following points into consideration:

  • The types of plants you can grow in cold frames depends on the size and design of the coldframe.
  • Some plants fare better in cold frames than others.
  • The main conditions you will want to control/monitor are temperature, sunlight, moisture, and wind exposure.

 Three main types of cold frames:

1.  A portable frame with a rigid plastic cover is perfect to move around your garden.  It can extend the harvest of cool-season vegetables, and will allow direct-sow seeds earlier in the spring.  Always use cedar, never pressure treated lumber! The picture below is an awesome and easily portable frame Palram Cold Frame, Double

For more coldframes and greenhouse comparisons read our review of the top 10 Garden Greenhouses.

2. Sunken cold frame with field-stone, brick, or cinder-block walls acting as a thermal mass with a rigid plastic cover is best for over-wintering tender plants and hardening off seedlings.

3. If your budget is tight, a simple Zenport Cold Frame Greenhouse Cloche
can be used to warm the soil for spring seedlings, and protects frost-sensitive plants in spring and fall.

For more coldframes and greenhouse comparisons read our review of the top 10 Garden Greenhouses.

Starting Seeds Early

Whether you are starting seeds in flats, or sowing them directly into the soil, a portable cold frame provides the opportunity to get your plants going a few weeks early.

Coldframes eliminate the transplanting shock that many plants suffer from because they will be acclimatized from the onset.

If you are seeding in the early spring or fall, focus on cool-season plants, as they tend to have lower temperature thresholds for germination. Keep in mind that seedlings are more susceptible to extreme weather conditions than established plants.

garden cold framesIf you are sowing directly, start two weeks prior to seeding in order to warm the soil for germination. Keep the seedbed evenly moist and once seedlings have germinated, the cold frame should be vented frequently to discourage damping off by increasing air circulation.
When starting seeds in a greenhouse or under grow-lights, you can start them a good five to six weeks earlier than usual (March in my case) and transplant them to a cold frame outside in your garden. Do make sure you place the coldframes outside two weeks prior to transplanting to warm the soil up nicely while monitoring  the amount of sunlight, moisture, temperature, and wind.  A little trial and error will give you lots of knowledge for your specific micro-climate and garden situation so don’t give up!

Use transparent cover of plastic or glass as you are encouraging active growth.  Remember, the plants will need light. The soil will tend to dry out more quickly inside a cold frame than outside, so keep the soil moist, especially while the plants are getting use to their new site. Keep in mind that more plants die of excessive heat and drought in cold frames than from cold damage.  Proper ventilation is particularly important for cool-season plants. After you have established your transplants, vent the frame when the outside temperature is 40°F or higher. If your plants are closer to the seedling stage, you may want to wait until the outside temperatures are 45°F to 50°F before venting.


You won’t be able to keep your plants growing lushly through the deep winter months, but you can provide plants with the right conditions for a gentle dormancy, and they will be eager to resume growth come spring.

Controlling the weather conditions to maintain a healthy dormancy is crucial.  Here are some key points to keep in mind.

  • Keep the soil moderately moist but not wet.
  • Little sunlight to discourage active growth. I had success using a less transparent or white plastic covers on my cold frames limiting the amount of light penetration while controlling spikes in daytime temperatures.
  • Temperature fluctuations can be harmful to dormant plants so you should control temperatures by venting the cold frame. As a general rule, if it’s 35°F to 40°F and sunny, you should open the frame part-way, while at 45°F to 50°F, you may need to open it up entirely. Using a sunken cold frame is a perfect solution, and it will offer much-needed protection from extreme exposure. This is especially important for plants that still carry foliage in winter.


Hardening off seedlings

When plants are moved from a warm, sheltered location—such as a greenhouse or indoors into the outside garden, they must be gradually acclimatize to fluctuations in temperature, sunlight, moisture, and exposure. Generally this is done by carrying the plants outside and back in again for gradually longer periods of time over the course of a week or two. The same effect can be achieved by opening and closing a cold frame over a five to seven day period.

The trick to a successful hardening-off period is to keep track of the extended weather forecast and plan accordingly.

If you are  moving out cool-season or young perennial plants from the greenhouse, you will have to wait for a stretch of weather where the lows don’t fall below 35°F. Even if the temperature drops after this period, plants hardened off and growing in a cold frame will be fine. For warm-season plants, you would wait until the temperatures have stabilized and we are within two to three weeks of our last frost date.

In general, wait until seedlings have formed multiple sets of true leaves and are well rooted before moving them into cold frames. Once the plants are packed closely into a frame, start venting the frame during the warmest part of the day, gradually increasing the length of time the frame is left open. If you are not able to tend to the frame during the day, try to time the onset of your hardening-off period with cloudy weather, and start by venting the frame just a crack, gradually increasing the open gap each day.

As plants acclimate to cooler temperatures, more direct sunlight, and wind exposure, their foliage will often thicken and darken in color. New growth is also a good sign that the transition is going well and your plants are ready for their final move into your garden.

Extending the seasons

You can easily and affordably extend your growing season with a simple plastic hoop tunnel. you will get the same benefits of insulating the plants inside and keep frost at bay. An easy DIY way would be to use some rebar spikes with 6-foot sections of PEX pipe creating an arch. You can then stretch some clear or white plastic over these hoops. If you don’t feel like doing the work get one of these easy alternatives.

Happy Gardening!



  • Lula says:

    Always liked the idea of extending the growing season. What would be the advantage of using coldframes over greenhouses?

    • zolika says:

      Besides filling different needs, think of coldframes as a quicker cheaper and more felxible alternative to green houses. Green houses will be covered in a seperate article and will make sure I will mention the the differences. Happy gardening!

    • GreenGuru says:

      Besides filling different needs, think of coldframes as a quicker
      cheaper and more felxible alternative to green houses. Green houses will
      be covered in a seperate article and will make sure I will mention the
      the differences. Happy gardening!

  • Alli says:

    I have always wanted a green house, but I think this is a great first step. What kind of wood has anyone used and had success with?

    • GreenGuru says:

      Like always using natural-wood products around your garden is best. Cedar is frequently used for raised beds, green houses and it is a natural choice for a rot-resistant natural material. Cedar is has its ability from its natural oils to weather over the years. No wonder you can see 100+ year cedar railing in the countryside. Drainage and air flow should be optimized, using a
      professional-quality landscape cloth as this will allow drainage and air movement around your raised bed or greenhouse keeping the wood dry. Happy Gardening!

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