What is a cold frame?

Contents

Using Cold Frames In The Garden: Learn How To Use A Cold Frame

Greenhouses are fantastic but can be quite pricey. The solution? A cold frame, often called the “poor man’s greenhouse.” Gardening with cold frames is nothing new; they’ve been around for generations. There are a number of uses for and reasons for using cold frames. Keep reading to find out how to use a cold frame.

Uses for Cold Frames

There are a number of ways to build a cold frame. They may be made out of plywood, concrete or hay bales and covered with old windows, Plexiglas or plastic sheeting. Whatever materials you choose, all cold frames are simple structures used to capture solar energy and create an insulated microclimate.

Gardening with cold frames allows the gardener to lengthen the garden season, harden off seedlings, start seedlings earlier, and to overwinter tender dormant plants.

How to Grow Plants in a Cold Frame

If you are using cold frames to extend your growing season, the following plants grow well in a cold frame environment:

  • Arugula
  • Broccoli
  • Beets
  • Chard
  • Cabbage
  • Green onion
  • Kale
  • Lettuce
  • Mustard
  • Radish
  • Spinach

If you are using cold frames to protect tender plants from winter temps, cut the plants back as much as possible before the first fall frost. If it isn’t already in a pot, put it in a large plastic container and fill it with soil. Pack the cold frame with pots. Fill in any large air gaps between pots with leaves or mulch. Water the plants.

Thereafter, you will need to monitor the conditions inside the cold frame. Keep the soil damp but not wet. Cover the frame with a white plastic cover or the like to keep out most of the light. Too much light will encourage active growth and it isn’t the right season for that yet. The white plastic will also keep the sun from heating the cold frame too much.

Seedlings can be transferred to the cold frame or started directly in the cold frame. If sowing directly into the cold frame, have it in place 2 weeks before seeding to warm the soil. If you start them inside and transfer them to the frame, you can start those 6 weeks earlier than normal. Keep an eye on the amount of sun, moisture, temps, and wind within the frame. Seedlings benefit from warmer temps and moisture, but winds, heavy rain, or too much heat can kill them. That said, how do you properly use a cold frame to grow plants and germinate seeds?

How to Use a Cold Frame

Growing plants in a cold frame requires the constant monitoring of temperature, moisture and ventilation. Most seeds germinate in soil that is around 70 degrees F. (21 C.). Some crops like it a little warmer or cooler, but 70 is a good compromise. But soil temps are not the only concern. Air temperature is also important, which is where the gardener needs to carefully monitor.

Careful monitoring and response is important. If the frame is too warm, vent it. If the cold fame is too cold, cover the glass with straw or other padding to conserve heat. To vent the cold frame, raise the sash on the opposite side from which the wind is blowing to protect tender, young plants. Open the sash completely or remove it on warm, sunny days. Close the sash in the late afternoon once the danger of excess heat has passed and before the evening air turns chilly.

Water plants early in the day so the foliage has time to dry before the frame is closed. Only water the plants when they are dry. For transplanted or direct sown plants, very little water is necessary since the cold frame retains moisture and temperatures are still cool. As temps increase and the frame is open longer, introduce more water. Allow the soil surface to dry between watering but not until the plants wilt.

The Benefits of Using a Cold Frame

Posted January 24th, 2013 by Garden & Greenhouse in Greenhouse & Indoor Gardening Articles, April 2013

One of the most valuable tools in a gardener’s arsenal is the cold frame. A cold frame is a small, unheated greenhouse that creates a microclimate by trapping solar energy to warm the plants inside. A cold frame also protects plants from potentially harsh environmental conditions. There are many different types of cold frames and they can be built from various materials. Regardless of the style or materials used, as long as it is an enclosure that allows sunlight in and can be sealed enough to trap the sun’s heat, it can work as a cold frame. The two most common types of cold frames used by hobbyists are box style and hoop-house style.

The box style cold frame is nothing more than a bottomless box with an angled, transparent top. Box style cold frames can be built from a number of materials as basic as a box made of cinderblocks with an old sheet of glass on top or as technologically advanced as a composite structure complete with thermostat and auto-openers. Box style cold frames can be used to either house plants in containers or be placed over plants which are in the ground. Most hobbyist horticulturists looking to start their own seeds in a cold frame choose some variation of the box style.

The hoop-house style cold frame is an arched structure commonly constructed out of PVC or conduit slid over metal stakes that have been driven into the ground. The metal stakes act as anchors and the PVC or conduit material is bent over the desired area creating an archway. The PVC or conduit material create the “ribs” of the cold frame which is covered with some sort of transparent plastic sheeting. This style cold frame is usually chosen when a large area of frost sensitive plants needs protection from the elements.

Cold Frame Benefits

Gardeners that utilize cold frames could gain a few different advantages. Getting an early start on the outdoor growing season is probably the most common benefit reaped by hobbyist horticulturists. With the use of a cold frame, gardeners can get their starts acclimated (hardened off) sooner which allows them to plant larger, more robust plants into the ground. Cold frames will keep the soil and plants contained within approximately 5-10 degrees warmer than the ambient outdoor temperature. This usually allows gardeners to start the acclimation process a couple of weeks before the average last frost date in their area.

Another advantage of using a cold frame is it allows growers to extend the growing season for a number of weeks. This is great for plants that would otherwise wither and die at the first sign of fall. Extending the harvest also means you get to enjoy your own home grown veggies for a longer period of time.

Some gardeners, depending on their geographical location, use cold frames throughout the winter to either protect dormant plants until spring or to continue to harvest root vegetables and cold tolerant greens. A sunken cold frame or one that is at least partially buried under ground are the best types of cold frames for the hobbyist looking to overwinter dormant plants.

A favorite benefit of using a cold frame is it saves money. By using a cold frame to start your own seeds in the spring you don’t have to purchase starts from a nursery. Starting your own seeds also gives you the “pick of the litter” when it comes to choosing which plants you will use and which you will discard. The last two growing seasons my vegetable garden has been prolific and produced more than when I was purchasing starts from a nursery. Cold frames allow any gardener to start their own seeds. This is a huge advantage in itself because it reduces the likelihood of pest insects or other pathogens you may acquire from purchased starts. Besides avoiding the nasty headache of dealing with an infestation, this also saves money otherwise spent on pesticides. Extending the growing season with a cold frame saves money too. When using a cold frame in the fall you extend your harvest of edibles which negates having to buy them at the grocery store.

Last year I made a couple of box style cold frames out of some old windows that the previous owners left behind in our barn. It was surprising how much we ended up using them. We used them to start all of our vegetable seeds, acclimate our herb starts and grow winter lettuce and kale in the fall. After you build or acquire a cold frame it’s really easy to get started using it.

Starting Seeds

To start in early spring, choose cool-season plants as they will germinate in colder temperatures. You can either plant the seeds in trays or directly into the ground (assuming you have a portable cold frame). If you plan on sowing directly into the ground, be sure to place your cold frame in the desired location a week or so before you begin. This will allow the soil to “warm up” and become ready for planting. If you are growing warm-season plants (most vegetables), you should be able to start your seeds a week or two prior to the average last frost date in your area. Cold frames are great at keeping in the sun’s heat and protecting plants but they are not invincible to drastic weather conditions. Seedlings are very sensitive to temperature fluctuations so it is very important to check on the latest weather conditions. It may be necessary to find an indoor area at night if the temperatures are predicted to drop significantly. We moved our seedlings indoors a couple of nights last year. They may have been alright but it is better to be safe than sorry.

Acclimating (Hardening Off) Starts

In order to properly acclimate starts to outdoor conditions they must be slowly exposed to their future environment. A cold frame works great for keeping young plants sheltered while allowing them a “taste” of outdoor life. The process of acclimation, commonly referred to as hardening off, lessens the chance of transplant shock and thickens the cuticle (the waxy protective covering on the leaf’s surface) which reduces the amount of water the plant will transpire. Plants started indoors or purchased at a nursery can be placed directly into the cold frame for acclimation.

As with seedlings, cool-season plants can be started earlier while most warm-season plants can begin the acclimation process around two weeks prior to the average last frost date. If your cold frame is portable, start in a shady location. Throughout the next week you can slowly increase the exposure to direct sunlight. If your cold frame is stationary, or you don’t want to move it, a small section of shade cloth can be used to limit the exposure to direct sunlight. Each day you can remove the shade cloth for longer periods of time until the plants are acclimated. Most plant varieties will be fully acclimated within 7-14 days when using a cold frame. We acclimated the herb starts we purchased at a local nursery in our cold frame. I got a little anxious to get them in the ground so they were only acclimated for 5 days. I noticed a slight case of transplant shock on a few varieties which I believe was preventable had I been patient and given them a few more days to acclimate in the cold frame.

Extending the Growing Season

Hoop-house style cold frames built right over the rows is a common method of extending the season with a cold frame. Portable box style cold frames can serve the same purpose although usually for a smaller area. I used our cold frames to plant winter lettuce and kale in late summer. This worked great at extending our very short growing season. It felt good to harvest fresh greens long after most gardeners in my area had hung up their hoes. Broccoli, swiss chard, kale, carrots, beets, and winter lettuce are just a few of the veggies whose season can be extended into winter by using a cold frame.

Cold Frame Maintenance

Cold frames are great but they are not a “set it and forget it” apparatus. Unfortunately, there is a little work that is required to ensure your cold frame works for you and not against you. Solar energy is a very powerful thing. It is very important to open a cold frame on warm, sunny days. Gardeners using cold frames must be very aware of the weather conditions. Even late into the fall, my plants could have been cooked alive had I not cracked open their enclosure on sunny days. Squatters can cause additional maintenance as well. A cold frame’s warmth and protection can be very inviting to insects and critters (we had ants and wasps try to make their homes in ours last year). Condensation is very common in a cold frame. This will cloud up transparent material and possibly create an environment for molds or fungus. Regular cleanings should be scheduled to not only retain the transparency but also to reduce the chance of harboring unwanted pathogens.

Not all gardeners have the space or the means to have a greenhouse but every gardener could reap the benefits of a cold frame. Cold frames are easy to build and can take up as much or as little space as desired. Many cold frames are constructed from recycled materials which makes them free or very inexpensive. Even if you choose to purchase a pre-built cold frame from a manufacturer it is absolutely worth the investment. Cold frames allow gardeners to get an early start on the season, extend their season and save money. Those three reasons, combined with relatively easy accessibility, are why every horticulturist should have a cold frame.

Eric Hopper resides in Michigan’s beautiful Upper Peninsula where he enjoys gardening and pursuing sustainability. He is a Garden & Greenhouse contributing editor and may be contacted at [email protected]

Want more information? Read these articles:

A Cheap and Easy Seedling Greenhouse

Cooking up a Lasagna Style Garden and Using Cold Frames to Extend the Growing Season

Cold Frames and Cloches

Extended Harvest Planning – Get Acquainted with Cold Hardy Vegetables

Make Your Own Cloche from Anything That Will Work

Understanding Polycarbonate Greenhouses

How To Build a Cold Frame with Straw Bales

The bales are also good for stacking into play forts, but this time of year, when nights are still cool and the vegetables of summer are calling to be planted, straw bales suffice as building material for a tiny greenhouse, also known as a cold frame.

Like a greenhouse, a cold frame gives you a head start on the growing season so tomatoes, peppers and other vegetables that shiver when the temperature drops below 50 degrees (and keel over when it drops below 32 degrees) have the sauna-like conditions they prefer, even when it’s cold outside.

The concept is simple: the bales are used as an insulated wall and a couple of old window frames make a roof that lets the sun’s rays through, but prevents heat from escaping.

If you want, build your cold frame over an existing garden bed and plant directly into the soil, or build it on any level patch of ground and place flats of potting soil inside for starting summer seedlings.

You Will Need

Straw bales*

Old windows**

8 pieces of ½-inch by 24-inch rebar

2 8-inch wood stakes

A ‘mini’ sledgehammer

*Straw bales, which are made with just the stalk of the grain, are preferable over hay bales, which include the seedhead of the grain and are intended as animal fodder, not building material.

**The total window area should be roughly 4 to 6 feet by 4 to 6 feet – the exact dimensions aren’t that important because the structure can be adjusted to match. The number of bales needed depends on the size of the windows, as well as the size of the bales.

Step One – Arrange the Bales

Determine which direction is south (hint: it’s at the midpoint between where the sun rises and where it sets) and arrange two bales lengthwise facing that direction. Then place a bale on either end in a perpendicular position to form a three-sided structure. These two bales should be placed so they rest on their skinny side, making them taller than the first two.

Step Two – Place the Windows

Lean the windows against the shorter bales at the back of the three-sided structure, allowing the other edge to rest on the ground in front (this creates a slanted surface that is angled toward the sun as it passes through the southern half of the sky). Now, adjust the two side bales to close off the space between the windows and the ground. Drive a wooden stake in the ground at the base of each window so they don’t slip off the straw bales at the other end. Larger windows may require an additional bale on each side to close off the space between the windows and the ground.

Step Three – Secure the Bales

This is optional, but a good idea if you want the most airtight and secure cold frame. If you are only using the cold frame for a couple of months, you can skip this step. You may need a couple of friends to help with this part. Slide a big handful of loose straw between the two rear bales to fill in the gap where they meet as if you’re chinking the logs of a cabin. Then have two people push the bales toward each other while you pound a rebar stake through each side of the two bales to hold them in place. Add more straw between the side bales and rear bales, if needed.

Cold Frame Tips

The windows function as a lid to provide access to the plants inside the cold frame, as well as to provide ventilation so the plants don’t overheat. When the sun is shining, the temperature inside a well-sealed cold frame may be twice the ambient temperature. In sunny weather, prop the windows open a few inches whenever the temperature goes above 40 degrees. If temps are above 50 degrees, remove the windows entirely and return them to the closed position as the sun sets, trapping the heat inside. During early spring, the lid of the cold frame will generally be open during the day and closed only at night.

How to Build a Straw Bale Cold Frame

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Make a simple DIY straw bale cold frame using old windows, to either harden off your plant starts or to extend your growing season!

Today I am going to share with you how I created more room for my plant starts. My growing rack was getting full, and I came up with this simple DIY project, making a straw bale cold frame with old windows we had lying around.

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How to Harden Off Your Seedlings
Simple Easy Gardening, Use Mulch for No Weeding!
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DIY Straw Bale Cold Frame

It’s so simple, it will only take a moment to tell you how we built it. We bought six bales of straw. The straw will be reused later, for mulching in the garden. Don’t use hay if you want to mulch with it. Hay has lots of seeds in it, straw has less.

We had 3 windows lying around, that had blown their seals. So six bales of straw was the perfect size for us. Depending on what old windows or glass doors you can get your hands on, you may need to buy more or less.

We simply placed 2 bales end to end on the long side, 1 bale on each end, and placed the windows on top.

Hardening Off Plants in a Cold Frame

We built this cold frame to have additional space for our veggie starts. I needed my growing rack to start peppers and tomatoes, but it was full of celery, asparagus and artichokes.

If it is still cool out, this works very well. We had a heat spell this week, where it got in the high 70’s and low 80’s. We actually had to shade some of the starts from direct sunlight it was so hot! So be careful on warm days that your plants don’t cook in there.

Also, be aware of fire hazard, if you leave the windows on and it gets very very hot. Straw is extremely combustable, so be sure that you are venting the cold frame properly in hot weather.

Venting the Cold Frame

Even on not so hot days, be sure to open the cold frame up and vent it appropriately. We only have it completely closed up at night, and on days where it is 40 degrees or less.

As it gets closer to actual planting time and continues to warm up, you should have it open more and more. Even at night as you slowly harden the plants off.

Extending the Growing Season with a Cold Frame or Greenhouse

Not only can you extend the growing season by using the cold frame in late winter/early spring for hardening off plants and housing your veggie starts, but you can actually grow in it! Especially with this straw bale design. If you wanted to fill in the center of the cold frame with soil, you could start growing greens and other cold hardy vegetables such as brassicas or root crops in there in winter with the windows on top for a spring harvest.

You could also do the same thing in fall and early winter. Simply plant a fall crop of greens or brassicas or root crops and they should do fine temperature wise in there for quite some time. Plant growth may slow down as the daylight wanes in mid winter, but should resume as the days lengthen.

I also love my greenhouse for this reason. It is a plastic greenhouse, unheated, almost more of a high tunnel really. But it has served me well over the years. It allows me to move my tomatoes and peppers into it the first weekend in April, and they are usually still producing into October for me. Which for the PNW is pretty incredible as we have such a short growing season here.

Eliot Coleman, the Master of Winter Gardening

To learn more about 4-season gardening, extending the growing season, be sure to check out the book The Winter Harvest Handbook: Year Round Vegetable Production Using Deep Organic Techniques and Unheated Greenhouses by Eliot Coleman. He lives in Maine, and is a market gardener, who grows food all year long. In Maine. Through the winter. Yes, he really knows his stuff!

Beware of Mice, Voles and other Vermin

A perfect warm and cozy home for mice and voles, so be aware!

One thing to be aware of in either a cold frame or a greenhouse, are mice, voles and other vermin eating your plants. They are known to love to nibble the tops off of your brand new veggie starts. In the dead of winter, they will find your root crops if you have them growing in there, they will eat them too.

So be sure to have some type of mouse/vole trap in place. Eliot Coleman has a great design for a DIY trap, that I found some pictures of in this excellent article: Extend the Growing Season with Coleman’s Double-covered Low Tunnels. They also talk about the trap and how it works in this article. Scroll down and on the left hand side, you can see two pictures of a wood box with mouse traps inside.

Reusing the Straw Bales

The benefits of a straw bale cold frame, is that you can re-use the straw bales for other things when you no longer need the cold frame. I prefer to use my straw for mulch in the garden. Which prevents weeds, see my article here on The Secret to Easy Gardening, No Weeding!. It could also be used as animal bedding for goats or chickens or what have you.

As I mentioned above, you can fill in the cold frame with soil, and use the straw bales as your raised garden bed supports. Another option, is to also garden right inside the straw bales themselves. Simply use a pointy trowel, dig out a hole in them, add some compost and plant your plant! This is also known as straw bale gardening. There are lots of sources online about it and I have two personal friends who only garden in straw bales, so I know it works!

Simple Straw Bale Cold Frames – for Winter Gardening

Simple Straw Bale Cold Frames – for Winter Gardening

  1. 1. Simple Straw Bale Cold Frame by Sue Mullen Living in a straw bale house has expanded my lifestyle in many ways. Since that first building project five years ago, i’ve enjoyed discovering many more uses for straw bales. Reclamation of overgrazed land eats up a lot of them. I generally re-seed with locally gathered native flower and grass species, and then lay down enough straw to completely cover zhe ground It’s not as much mulch as I’d like to use, but I’ve got a lot of ground to cover. some of the seed always germi- nzzes, and the mulch helps to slow down and infiltrate surface runoff from heavy rainfall. In addition, the soil retains more moisture, and the mulch offers a home to any wind scattered seeds. Some of my other straw bale uses include makeshift privies, compost piles, saw horses, microclimates for border- line cold sensitive species (my fig tree), and cold frames. 13 Perma culture Drylands Joumal For a salad lover, the straw bale cold frame is the most rewarding use of bales. IfI already have salad greens in production as winter approaches, I simply enclose the bed with bales, and cover with pieces of corrugated fiberglass roofing. These are held in place by cement blocks, bricks, or rocks. My cold frame encloses a bed about 4 by 12 feet, and uses 10 bales. The bales on the south side lie flat, and those on the other three sides are placed up on edge. This gives a little more southern exposure. The climate inside the frame stays warm, moist, and protected. This winter garden always yields the best salad greens of the year—very tender and sweet. The roofing pieces provide easy access to separate sections of the bed. I usually sit or kneel on the bales to gather the greens. IfI’m weeding, transplanting, or if the bales are really wet, I simply roll a couple of bales away, do my work, and roll them back when I’m through. As spring approaches, and the days get warmer, I like to remove the roofing during the day, replacing it at night. When I feel that the bales are no longer necessary, I dismantle the cold frame and use the straw for mulch. Be creative, and let us know what works for you!

Learn how to make a cold frame for the garden with these tips. When those first frosts of fall hit, you’ll want to protect your precious plants!

What are Cold Frames?

At their simplest, cold frames are bottomless boxes that are set over plants in the garden to protect them from adverse weather. They are usually built low to the ground and have a transparent roof to let in light and a hinge for easy access.

Why Use a Cold Frame?

Cold frames protect plants from strong winds and retain heat. Gardeners use cold frames to extend their gardening season—both in the autumn to protect plants for a few more weeks and in the spring to get a jumpstart on sowing seeds. Cold frames are also used to “harden off” seedlings that were started indoors.

  • Try sowing seeds of crops such as radish, lettuce, endive, and scallions directly in the frame for an early or late harvest.
  • You can even raise them there all summer as long as the cover is removed when warm weather arrives.
  • Consider growing winter lettuces or other salad greens, like spinach or kale.

How to Make a Cold Frame

Cold frames can be bought or constructed from timber and plastic, but concrete blocks or bricks can also be used. You can even construct a simple, bottomless wooden box and set it in the garden or atop other good soil in a sunny location. Watch our video, below, for step-by-step building instructions!

Cold Frame Building Tips

  • Most gardeners use wood to build the frame, since it’s readily available and is easy to cut to the required size using hand tools. If you’re lucky enough to find scraps of hardwood, then use this, as it will last longer than softwood.
  • Avoid old wood that’s been treated with creosote or similar non-earth-friendly products, especially if you’ll be positioning the cold frame directly on the soil. The wood can always be painted with a non-toxic paint if you’re worried about it looking scruffy.
  • Top the box either with glass (perhaps an old storm window) or a frame covered with clear plastic. Thicker materials will provide more insulation, of course. Old windows and shower doors are classic subjects for this project. Hinge the cover or add a sliding lid so that it may be opened for ventilation on warm days.
  • If you have high-sided raised beds, you could add a sheet of glass on top to construct a temporary cold frame.
  • Temporary frames or “cloches” can also be made by leaning old storm windows tent-style over the plants along the length of the garden row.
  • For those of us with limited time and/or DIY skills, try cutting the bottoms out of plastic milk jugs and placing them over individual plants, holding the jugs in place with mounded soil. During sunny days, remove the caps for ventilation.

How to Make a Hot Bed

A hot bed is a cold frame that is heated. Some gardeners use electric heating tape or cables, but the age-old method of using horse manure or compost works well, too.

  • For a nonelectric hot bed, excavate 18 to 24 inches under the frame and add fresh manure or compost.
  • Turn and moisten this material every couple of days for a week until it settles, then cover it with 6 inches of soil.
  • As the manure or compost decomposes, it will generate enough heat to protect against early or late frosts.

See our video with step-by-step instructions on how to build a cold frame.

Do you use a cold frame or hot bed in your garden? Share your technique in the comments below!

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Cold frames are a great season extension tool to help you garden in cold weather or to start warm weather seedlings long before your last frost date. Learn all about cold frames (including DIY cold frames) in this article!

Cold frames: a useful resource for cool and cold-weather gardening

Have you ever tried to start seeds indoors and ended up with anemic, gravity challenged sprigs? Bright, direct light is vital to emerging seeds and most windowsills are not sunny enough.

This leaves you with two options:

  1. indoor grow lights (like the DIY grow light system we recommend), or
  2. real sunlight with cold protection.

Artificial lighting (grow lights) is an ideal choice if you have the indoor space. If your indoor space is at a premium but you want to start garden seedlings to get a jump start on the growing season, cold frames are your best bet.

Thankfully, cold frames are also easy and inexpensive to build!

Not everyone has a greenhouse like this. Cold frames are a more frugal option for both money and space.

A cold frame is exactly what it sounds like: a transparent outdoor frame that protects plants from cold weather while still letting sunlight in.

This means your plants get natural sunlight and extra warmth. In most regions, a cold frame can be used effectively to grow winter seedlings and crops, though if you live in a climate zone below USDA Zone 6, you may need a more fortified version than the one I use in my garden.

A cold frame can be constructed from materials you can easily find. This one, photographed in Asheville NC (zone 7a/6b), is made from lumber and some old windows. Notice the rocks around the cold frame as well, which trap heat, helping to create a warmer microclimate.

Also, if you don’t feel like making your own cold frame, you can order a really good Austrian/German-designed cold frame via Amazon. It’s double sided (more space), made of durable materials, lets in light from all angles, and you probably couldn’t make it more affordably if you were to buy all the pieces/parts yourself.

How to make cold frames

Cold frames are typically unheated. All their plant-protecting power comes from solar energy stored in the structure and soil during the day.

Parts of a cold frame:

Top – A light-permeable cover such as glass, plexiglass, or greenhouse plastic is used for the top of a cold frame.

Sides – The sides are made of any material that will create a supportive structure for the cover.

Bottom – A bottom is not necessary for your cold frame. Most people just use soil. If you decide to create a base for your cold frame, make sure it allows water to drain.

Our cold frame constructed from straw bales and recycled windows.

We used recycled windows for our cold frame. Some of them came from a friend’s farm, some of them came from my husband’s coworker, and some of them came from our local Habitat for Humanity store.

Glass is the most transparent and permanent material you can use… unless you live next to children playing ball or position your cold frame under the Whomping Willow (or any aging tree).

Depending on how cold your weather gets you may want the straw bale joints on your cold frame to overlap more. In very cold areas be sure to stuff any gaps with loose straw or leaves.

Available materials and permanence: considerations when constructing your cold frame

Straw has been our material of choice for the sides of our cold frame. Why? Straw bales are:

  • thick and very insulating,
  • easy to come by (garden, home improvement, and farm stores all carry them),
  • relatively inexpensive (in bad hay years the price goes up),
  • fully biodegradable when we are finished with them,
  • extremely easy to assemble.

At this point we’ve been using straw for 3 years and have found it perfectly suited for our needs. I had given up on shelf greenhouses or ever getting around to building a wooden cold frame and was carrying my seed trays in and out of the house on warm days. Needless to say I am much happier with our cold frame!

Note that you don’t have to use straw for your cold frame! People also use lumber, bricks, and many other materials to create cold frames. Use what’s easily available and/or within your budget!

Easy to assemble, easy to disassemble

In our case we don’t have a permanent spot to keep our cold frame in, so it has moved around the past 3 years. Sometimes it is in our driveway, sometimes next to our shed, and sometimes it is out in the garden.

That means our building materials and cold frame needed to be:

  • easy to carry, and
  • easy to take apart and put back together again.

When the summer plants are dormant we could even put a temporary cold frame on top of one of our late-emerging beds.

Plants stay toasty warm inside, but so do the critters! Watch out for slugs and other plant-munchers.

Recommended placement of your cold frame

You can put a straw bale (or any cold frame) just about anywhere in the yard. However, the best places get south-facing sunlight for early morning sun.

The least effective placement is on the north side of a house, building, or tall tree (not enough sun).

Seed trays and potted plants aren’t the only use for a cold frame. You can put them directly over a half-hardy plant in the garden like these golden snow peas and remove the structure when the weather warms in the spring.

Ideal plants for cold frames

Since the plants inside will only be a little bit warmer than the outside air, cold frames are mostly used for frost-tolerant crops during the winter. Check out our article Easiest plants to grow in the fall and winter, for a complete list of frost-hardy plants.

Spring transplants under cold frames

You can also use your cold frame to grow out your spring transplants. If you do, you’ll want to pay careful attention to the weather and bring the more tender seedlings inside on nights when it drops below freezing.

Don’t forget that all sugar, snow, and shelling pea varieties have edible greens. Plant Austrian winter peas or any other type and harvest salad greens all winter long.

Too cold – Although most winter crops are at least a little bit frost tolerant, they don’t grow when it is under 40 F outside. They’ll appreciate the cover of your cold frame staying on any time the weather is below 50 F.

Too hot – Likewise, cool weather crops don’t like it hot. If the thermostat says 50 F or warmer, crack the cover or take it off completely.

You’ll start to get a feel for how warm or cool your cold frame stays as time goes on!

These tomato seedlings were grown out in our straw bale cold frame.

As the weather warms…

By spring, you’ll start leaving the cover off of your cold frame all the time. We usually leave our cold frame up until we’re well past any freak late freezes.

Then we give the straw bales a second life by spreading them under our rows of blackberry and raspberry brambles. When the berries leaf out and send out new canes they rest on top of the bales and block light from competing weeds. While the bales are under the brambles, they become hosts to mushrooms and other soil organisms.

We think the summer mushroom colonies mycoremediate any herbicides the previous farmer used. Ideally, you can find straw bales that don’t have pesticide residue so this issue doesn’t have to be a concern.

By fall the bale weed barrier has rotted enough to lose its form. The bales get a third life in the garden when they’re dumped in the chicken run to be dismantled as a precious feast by our laying hens. At that point they become compost that we can use to fertilize our next batch of seedlings!

One of our chickens enjoying what’s left of a straw bale.

We hope this article helps you better understand what cold frames are, how to use them, and how to build one yourself.

Happy gardening!

-Eliza @ GrowJourney
Master Gardener, Master Naturalist, Permaculture Instructor

Sometimes our articles will contain Amazon affiliate product links. These products have been carefully curated by our team. We use them, trust them, and know they work (or in the case of books, know that the information is extremely helpful). GrowJourney may earn a small commission on any sales that are generated via these affiliate links (without any additional cost to you).

It is often seen as the poor relation to a greenhouse, but if you reckon a cold frame won’t earn its place in your garden, think again. Even the smallest of gardens can accommodate one, giving protection to a succession of seedlings, young plants, succulents, alpines and herbs throughout the year, and extending the growing season by a few valuable weeks.

It’s a simple idea: a cold frame is a box with a sloping lid that can be lifted and lets light in. You can knock one together yourself, or spend anything from £30 to £1,000 buying one ready-made.

In spring, use a cold frame for early sowings of broad beans, sweet peas and lettuce in February and March, then from April to June fill it with hardy annuals, half-hardies, plants for the veg patch and tender bedding. Seedlings started off indoors can be weaned off the warmer, protected conditions of the windowsill in a cold frame, too.

During summer, most cold frames fall empty, but this is the perfect time to sow biennials such as stocks and sweet williams for next spring. Sow into seed trays in your cold frame and they’ll be protected from downpours and out of reach of curious pets and wayward footballs.

By September, with biennials planted out, the cold frame can become home to autumn-sown hardy annuals which will happily overwinter here. Try an autumn sowing of winter lettuce, pea shoots and oriental leaves in planters to provide salads up to Christmas.

Plants that don’t like sitting in wet compost over winter, such as succulents, alpines and some herbs, can be kept dry in the cold frame. And if you’re into propagating plants, it is a viable alternative to a greenhouse for storing cuttings through the year.

Siting your frame

Place your cold frame somewhere sunny and sheltered, so plants and seedlings get as much light and warmth as possible. A patio provides a stable surface; at an allotment, a few flagstones will do the trick. Or position it on top of the soil, using it as a large cloche when sowing or planting directly into the ground. Placed next to the house, a cold frame will benefit from the warmth of the building.

Check your cold frame every day or so, especially when it’s warm and sunny, to see if anything needs watering. Hunt out pests, such as slugs lurking under pots or greenfly on leaves, which can cause havoc if left unchecked in a small space. Ventilation is important: even in early spring, heat can build up quickly, causing young plants to wilt. Opening the frame occasionally in autumn and winter will help prevent damp, stagnant air building up – the perfect breeding ground for fungal diseases. Remember to close the frame at night to protect from frost. Every so often, clean the lid; it’s surprising how much dirt builds up and blocks valuable light. In very cold winters, place old blankets, bubble wrap or layers of newspaper on top of the lid overnight.

Buy or build

For a rustic-looking and inexpensive option, it’s easy to create a cold frame from bricks or wooden pallets and salvaged windows. Look in skips, salvage yards and on Freecycle.

There is a wide range of cold frames for sale, made from aluminium or wood with glass, polycarbonate or plastic for the lids. It pays to buy the best you can afford. Aluminium frames are lighter, cheaper, require no maintenance and should last a lifetime. Wooden frames are sturdier, provide better insulation and look more attractive, but are more expensive. Glass is best for allowing maximum light in and retaining heat, but if you have young children or pets, a polycarbonate lid is a safe alternative and provides more insulation than plastic.

The Greenhouse People has basic cold frames made from aluminium and polycarbonate for as little as £35. A good mid-range option is its 3ft x 5ft (91cm x 152cm) treated wooden frame with glass for £250.

Or go for a tiered model, such as Gabriel Ash’s Upright (height 1.4m; £822) or Harrod Horticultural’s Hardwood Plant House (height 1m; £179.95). Both come with adjustable shelving and allow you to grow taller plants.

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This post below was written for us by our friend Scott Allison. As we all know, straw has multiple uses and this is a pretty easy/economical/functional use for bales. This is a quick a simple project that you can do to extend your growing season. The details below are for a simple, what I would call “annual” cold frame. In other words, this would need to be rebuilt each year because it is not plastered and protected from the elements. That said, it could be upgraded with ease to be a permanent structure if that’s what you are after. Here’s what Scott had to share:

As a sustainable builder I have always loved working with natural materials and I myself have a fondness for reusing as much as I can whenever I can. So when my friend and long time client asked me about building a cold frame on the south side of her little urban farm I thought it would make sense to work with straw bales.

The project took me just a few hours to complete and I was working by myself.

First I built what I understand to be a Ben Franklin style foundation with out infill other than a few cross red bricks to keep my spacing. With hindsight I would suggest a few screws and fastening some 2×4 spacers to keep the foundation from falling on its side while placing the bales.

Second I placed the bales side by side. Two high on the north side and a single row on the south. Then I took apart a single bale and stepped the sides down, filling in where I needed to.

Next, I placed wooden spacers on the top of the north and south rows and screwed them into wooden 1×1’s so they would support the poly carbon plastic panels on top. The 1x material can be doweled into the bales to keep it in place and the poly roof attached with roofing screws (with washers) to the 1x runners.

I planted a few broccoli, arugula, lettuce, collard greens, and chives and they all seem really happy. The night that I built the cold frame turned out to be the second frost in our area; however, the temperature inside the cold frame stayed well above freezing. The broccoli is now blooming so I think it’s gonna work pretty well. I intend to place some red brick towers in the north side corners as thermal mass and I imagine a few candles (in coffee cans of course) might go a long way to make for a really warm place to grow food during the winter.

I hope you enjoy the concept and creation,

Sustainably yours,

Scott Allison

GaianlogicConsulting.blogspot.com

503.886.9731

Living Off The Grid: Straw Bale Cold Frames 101

The end of the growing season for passionate gardeners can be a bummer. But, to anyone who wants to grow food longer and start it out earlier, this is the article for you.

Being self-sustainable in every way possible is great, so growing your food – and as much of it as you can – is important. Cold frames are a great addition to any garden because you can use them to lengthen your growing season, both by giving plants longer to grow before it gets cold and also by allowing you to start some seedlings early.

What is a cold frame? A cold frame is literally a frame used to protect your plants from the cold. There are several different versions and methods you can use to create your cold frame. Some like to build their own, while others like to look for materials they can reuse or re-purpose.

Your cold frame can be super elaborate, or you can give it the rustic homestead look. I’m going to go over the basic materials that are used when constructing a cold frame: you just need four walls and some windows. Some people prefer a permanent and stationary cold frame while others prefer a temporary version. This article covers the temporary version below.

Straw Bale Cold Frames

I love this version of the cold frames because it is temporary, easy to set up, and the straw bales provide much-needed insulation, especially in colder climates. Always be sure you have a way to open the cold frame easily – this makes it easier for you to access the plant and the plants can get some fresh air during warmer weather.

All you have to do is get enough brick straw bales to enclose the area of choice. You can make your own windows by building a simple frame and use some greenhouse plastic as the actual window. You can also use glass, of course. I just used some old windows I found and they worked perfectly. Try to avoid windows with cracks or chips in them as it will allow cold air in and can cause injury later. Put your windows over top of the enclosure and you’re all set!

As I mentioned earlier, this is one of the easiest methods. You can also build your walls using: Bricks, Logs, Boards, Wood, Old Doors, Old Refrigerators, and basically anything else that can provide solid walls for the windows to sit on.

You can incorporate all sorts of different materials to construct a cold frame. Another reason I like the straw bale version is not only am I reusing and re-purposing old material but I can reuse and re-purpose the straw also. When I am completely finished using the cold frame for the year I store the windows and take the straw, which may be breaking down come spring, and use it all over the homestead. You can use it for animal bedding, compost, and mulch, just to name a few things.

Now that you know the basics, let’s move on to the plants in your cold frame. Many winter crops will stop growing when the temperatures drop below 40 degrees Fahrenheit. Don’t get me wrong, winter crops are frost tolerant and will survive through the low temperatures; they will just not do any progressing. If you happen to have cool weather crops in your cold frame, be sure when temperatures reach 50 F or above that you open it up and let the plants get fresh air.

By springtime, the cold frame isn’t really necessary anymore so if you used the straw bale method just recycle the straw. If your method of choice was something more permanent or stationary you can continue to use it for growing food. Either way, it can be surprising how much more food you can get and how much faster you can kick off your spring planting.

Most salad greens will continue growing in a cold frame. Some other plants that will do well:

Spinach

Carrots

Chard

Scallions

Lettuce

Endive

Radicchio

Mache

Along with several other root vegetables. This is just a short list of the cold, hardy vegetables that thrive in a cold frame. The cold frame is also great for growing flowers and herbs. One last benefit to note is that having a cold frame will keep a majority of the wildlife out of the garden.

*Sustainable Suggestions*

When remodeling or making repairs to your home, save any of the good scraps for future projects, including nails and screws. This could save you money in a pinch, as well as saving more trash from a landfill.

Photo #1 Credit: “Finished Our Straw Bale Cold Frame Today” by The Bairds is licensed under CC BY 2.0

Photo #2 Credit: “Cold Frame Built with Bales of Straw” by Terrie Schweitzer is licensed under CC BY 2.0

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Now that the colder months are just around the corner, you might be wondering how you can save your delicate plants from the frost or even how to ensure that those vegetable plants you have been cultivating all year will still be ready to go in the ground once spring is sprung. Not all hope is lost when you think outside the box and get a little creative!

Table of Contents

Let’s Look Closer

There are ways to exercise your green thumb even when there is a foot of snow on the ground and the soil is frozen from the frost! With the use of an enclosed structure, you can protect your plants from damage due to frost and you can even continue to grow plants year-round. Some vegetables might even bare a harvest when grown properly in the right conditions and temperatures.

So how can you achieve this level of gardening year-round? With the use of a greenhouse or a cold frame. While similar, there are some key differences between a cold frame and a greenhouse. Curious about what those are? Well, you’ve come to the right place because we are going to break down a cold frame structure versus a greenhouse.

What are the Pros and Cons of a Cold Frame and a Greenhouse?

The biggest similarity between a cold frame and a greenhouse would have to be that they are both enclosed structures whose primary purpose is to shelter plants and seedlings from winter conditions, such as the cold winds, frost, sleet, and snow.
The biggest difference between a cold frame and a greenhouse is that a cold frame does typically use a heat source and might only stand a few feet tall; whereas a greenhouse is a tall structure that has heating and ventilation systems for a year-round controllable climate.

Cold Frame VS Greenhouse Comparison

Cold Frame ​​​Greenhouse
  • Does not require on-going maintenance for those who have a busy lifestyle
  • Cannot control the temperature inside the cold frame
  • Freezing conditions may require the use of a heat source which can increase utility bills
  • Protects plants and seedlings from cold winds, snow, and frost
  • Will use a heat source to encourage plants to grow year-round
  • Can control the environment (temperatures, air, etc.)

Cold Frame

Structure

A cold frame is an enclosed structure that is used primarily for the protection of plants and seedlings. The four walls are generally made of glass or wood with a removable glass or wooden top. The cold frame will have a more boxed in shape and depending on how it is built, it could only stand as high as three feet or stretch as long as six feet.

Cold frames are usually placed against an existing structure to provide a higher level of shelter from the harsh climate changes that can happen during winter months. Generally, heat is not used in a cold frame because those who want a heated structure will build a greenhouse if possible. The plants and vegetation that will be placed in the cold frame normally require some sort of protection, like burlap wrapping or they are plants that can survive in the colder temperatures of winter but will be revived fast in the spring. Heat can be used in a cold frame, and that source of heat can come from a bottle of warmed water to an actual heater.

Maintenance

There’s not a ton of maintenance involved with cold framing, aside from checking every day to make sure no debris or anything has built upon the surface. When covered, even in the slightest way, not enough sunlight can get through to the plants. This is especially so in the winter months when the top can get covered in snow.

Cost

The cost of building or buying a cold frame highly depends on just that; whether you’re building it or buying one already made. Premade models range in price from $30-$100, depending on size. If you’re building one, it really depends on the materials you use, but should really only range from $30-$150.

Greenhouse

A greenhouse is an enclosed structure that has four walls, a roof, a doorway, a heat source, and a ventilation system. Typically built out of wood or wooden braces covered with glass or industrial plastic, the greenhouse will be tall enough for a grown adult to comfortably move around inside. Greenhouses are typically shaped like a little house, hence the name, with a peaked roof and ventilation systems for air and heat.

Greenhouses can be placed against an existing structure, such as a home, but normally are built to be by themselves in a section of the yard. A greenhouse requires ventilation, so the air doesn’t become too warm or moist, but it also requires a constant heat source to prevent plants and seedlings from becoming damaged due to the cold temperatures. Serious greenhouses will also require a lighting system that mimics the sun rising during the day and setting in the evening allowing for approximately 12 hours of darkness. This, of course, depends on the plants inside and their growing schedule.

A greenhouse can be a high-maintenance addition to your yard as it needs to be shoveled out, the walls must be structurally sound without any leaks, and it must be kept decently clean so that no bacteria or mites affect the plants you are trying to grow. The plants inside will also have to follow the same schedule as they do when they are outside in the ground, with watering, pruning and such.

Just like a cold frame, the cost of a greenhouse solely depends on whether you’re buying a premade one or building one. A ready-made greenhouse kit can be purchased for $200-$2000, depending on the size, quality, and materials used. If you’re building one, you can really keep the cost down while maximizing the size for less than $500.

Conclusion

Now that we have educated ourselves on the similarities and differences between a cold frame and a greenhouse, we can make the best decision to which one will benefit us the most in terms of our gardening needs. With a little bit of effort, supplies and time; you can have a cold frame or greenhouse installed right in your own yard. Some hardware stores even sell ready-to-assemble structures or if you prefer to do it yourself, then building plans and supplies are available at any local building supply store (supplies) and even online (plans)!

Speak to your local garden expert if you are unsure what the best option would be for the vegetation and greenery that is planted in your yard. Determine what size would not only fit within your yard comfortably but also will fit whatever plants that you want to protect.

Gardening is a wonderful source of exercise and it shouldn’t have to stop just because there is snow on the ground. Invest in a cold frame or greenhouse today and you too can garden the winter blues away by surrounding yourself with nature!

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Every gardener dreams of one day owning a greenhouse. It is an inevitable path that starts with a bit of fleece and the miracles of growth that happen with just a few extra degrees of heat, and ends in lusting after luxury bespoke greenhouses online and fantasising about pineapples. Growing under protection changes the game: seedlings grow strong and robust in a way that never happens on a windowsill. You can extend the season and ensure heat-loving plants still bake in less-than-perfect weather.

For me, this has been a fantasy for years. I have built lean-to structures, fashioned from skip finds, old windows and used fish tanks, but they have all fallen apart. This year, as I trawled through online sales of fancy glasshouses, I did a cost-per-wear analysis. I realise that such metrics are usually reserved for handbags and expensive jackets, but my world is floated by happy green things and my windowsills are starting to buckle and warp from years of seedlings grown on them. If I bought this handsome, tall cold frame, it would cost just under £20 a week. Put another way, every tomato I eat this year will cost me a pound – but oh, how wonderful they will taste. A single plant can produce up to 200 fruits, so from five plants I could harvest 1,000 tomatoes.

Runner bean plants. Photograph: Alamy

Tall cold frames are tiny lean-to greenhouses, perfect for patios and small urban gardens. They take up 2-3ft of width and can sit happily against a house or along a fence, or make good use of the side return. Any lean-to greenhouse or cold frame needs to face west. A south-facing wall might be toasty in winter, but come summer it will fry everything inside, even with shading. The area must be flat and not exposed, particularly to cold winds. Even a relatively gentle breeze of 15mph will double the amount of heat drawn from inside the greenhouse/cold frame.

‘Growing under protection changes the game.’ Photograph: Gap Photos

When buying one, look for a design with plenty of ventilation. Once the sun shines, the inside warms up quickly, the humidity changes and you get stale air – all of which is a recipe for breeding pests and diseases.

Ideally, you want roof and side ventilation, which creates a chimney effect: cool air is introduced from the side vents and hot air is expelled from the roof (which will be important come summer).

Finally, you’ll need shelving – the best sort is flexible, allowing you many shelves in spring for seedlings, but fewer in summer for large pot plants.

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