Extend the Seasons with a Cold Frame

comments (10) March 4th, 2009

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ChrisMcLaughlin Chris McLaughlin, contributor
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My Red Leaf lettuce in February.
Lolla Rossa lettuce
My monster-door cold frame.
My Red Leaf lettuce in February.Click To Enlarge

My Red Leaf lettuce in February.

Photo: Chris McLaughlin

Cold frames are basically very short greenhouses sans the heat. They are mostly used for extending the season in one direction or the other.

They are one of the handiest tools around for helping gardeners work around the weather we can’t control. In the fall, I use my cold frame to grow lettuces for the winter. When we’re facing spring, I pop my seedlings in it to harden them off before transplanting them into their permanent bed.

Cold frames are usually built as rectangular or square box structures that have a glass or plastic top. The glass or plactic collects the sun’s warmth to help extend seasons. They are super simple to make. I have done it two ways. I have used PVC pipe for the frame, and a long roll of plastic over the entire thing.

I did secure some small boards on the bottom of the plastic so the winds didn't pick it up and carry it off. But other than that, it worked very well. By the way, if you use curved PVC pipe covered in plastic to cover rows of plants, that would be called a "row cover", which accomplishes exactly the same thing.

Cold frame
  You can build a cold frame out of almost anything. This one sports a French door propped up with redwood boards.
Now, I have a very expensive cold frame (according to Bob). Bob was given a big French door for our home. Excited as he was to install it, apparently we have a Polly Pocket house compared to the house this thing came from. I suggested that we could recycle it and make it a cold frame – brilliant! He laid the beast on its side, and put it together for me (under his breath I heard him mumbling something about a thousand dollar door...bless his heart).

We (and by “we” I mean my husband-extraordinaire, Bob) cut three 2x4 redwood boards and secured them permanently to the inside of the door itself and the door fame below. We placed a board on each end and one in the middle of the frame. Hinges can be added so the lid can be set at varying heights, which is extra handy. I chose not to install hinges because I have a small granddaughter and that door is extremely heavy. Having the door secured in a fixed position was important to me for safety in this case.

Cold frames can be permanent or portable and it's a perfect way to recycle old windows, doors and the like. You could probably find some cool ones at a rummage sale, Freecycle or Craig's List. Once you have a cold frame hanging around the yard, you won't ever want to do without.

Cold frames for winter
If you have had the pleasure of being spoiled to cold-hardy veggies like home-grown lettuce and cabbage, you will appreciate a cold frame. Lettuce thrives in cool weather, and literally needs cold snaps for great flavor. That being said, the deeper we get into the winter, the cold can be tough on the leaves.

I start my lettuce seeds directly in the cold frame in the fall, and the lettuce hangs on for months. I’ve been harvesting lettuce since the end of January. If you are forcing bulbs for the winter, this frame can be used to give them the cooling period before they are brought in the house to bloom.

Cold frames for spring
In the spring, the cold frames are the perfect tool for hardening off (letting the plants adjust to the elements slowly) tender seedlings or small plants before they are planted into the ground.

They’re perfect for toughening up the seedlings you have so lovingly raised indoors. Take your seedlings outside and put them in the frame for a couple of hours, and then bring them back in. Increase the hours that you leave them in the cold frame for a few days so they become adjusted to the outdoors.

Once they have been out all day for a couple of days, you can leave them in the frame during the night as until it’s time to plant them in their permanent place in the garden.

This cold frame can give you a 12-month growing season.

More on cold frames:

Build a Simple Cold Frame
Give Your Cold Frame a Warm Bed
Top Your Cold Frame with a Lightweight, Snap-On Cover
• Cold-Frame Gardening 

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posted in: Projects, fall garden, cold frame, extend seasons, grow winter vegetables, harden off seedings

Comments (10)

BobMontesanoWA writes: Here in Montesano WA an alternative to lettuce in winter is corn salad or feldsalad (German, discovered visiting friends there, fall planted between the vinyard rows for winter salad) many types some over winter some more for summer. Eating some now mid December sown in mid late summer. Mid october sowing (probably should have sown earlier) is 2 leaf stage in the open garden and in an area next to house under a high porch but in the low angle winter sunshine and 4 leafs in the coldframe. I had the mature corn salad and the new sowing under the porch covered with tarps during recent low temps 16 degrees seldom above freezing and two snows over the last week. Temps are expected mostly above 32 for the next week so pulled tarps to give them some light. The tarped and cold frame plants looked great. The open garden plants in amongst the remaining snow looked a little beat up by the cold but should be fine just behind the cold frame and under the deck plants which will work well for harvest timing. Can be used as main salad ingredient or as a supplement to your other greens. Tastes great and gives a different texture to your salad.
Posted: 3:06 pm on December 11th
BobMontesanoWA writes: In Montesano, WA I use cold frame, hoops and plant in the open cold varieties of lettuce usually the red types named after some cold place. Sow in the fall and then transplant for spacing. They are small plants going into winter with just a few leaves. I have seen them coated in ice, temperatures in the teens or covered in a foot of snow thinking they would die but they slowly grow whenever there is enough light and warmth. Light seems to be the biggest issue. When it is cold the leaves lay flat on the soil outside but must be growing roots etc just like the weeds do because they take off as soon as conditions allow. Of course the cold frame produces the first harvests followed by covered and then by the open plants. I also plant green house raised lettuce when the first batches come to the stores usually too early to plant most things here but select the hardier varieties (seem to be varieties with red in leaves) and outplant with plastic liner on soil and may cover with plastic to help them get started. They are next on the table and then start to have other lettuce coming on in the garden from early sowing in cold frame. Best thing is that most of this happens while the slugs and aphids are absent or minimal.
Posted: 2:47 pm on December 11th
ColleenF writes: I live in Lake Charles, LA which is about 60 miles from Texas border. I like to grow salad greens and carrots in the winter. I grow tomatoes, bell peppers in the greenhouse all winter. My problem is not necessarily freezing, although it will do that occasionally. My problem is our weather goes cold/hot/cold and I find myself constantly checking the temps and opening/closing the greenhouse as well as cold frames, covers! Does anyone think that using hay bales would be more useful? I am willing to try anything!
Posted: 6:48 pm on October 19th
MaryMD writes: What is everyone elses experience with how low the temperature can get before lettuce or other cold-weather veggies are not protected by a cold frame? I am technically in USDA zone 5, but in the bottom of a mountain valley at 1600 feet. My experience is that cold frames, row covers, and even my greenhouse do not stay warm enough when the temperature gets to 25-30F.
Posted: 12:09 pm on February 3rd
Hoophound writes: We have been using mini-hoop houses, which have many of the attributes of cold frames, for nearly five years now and they make veggie growing so much easier. We use Mikroclima as the covering (which we now sell from our web site) and find that we rarely need to remove it.
But whatever the covering used I would certainly agree that protecting your plants is the way to go. Your plants love it and you get earlier and healthier veggies with less insect attack.
Everyone should try it!
Posted: 2:21 am on March 15th
mickie writes: My DH just built us a smalish cold frame in our back yard. This is going to be the first time either of us have ever used one. We live in western NY state. Any suggestions for Cold Frame Virgins?
Posted: 10:49 am on March 12th
ChrisMcLaughlin writes: Yes - another great way to use a cold frame! This is a whole other article. *grin*
Posted: 1:46 pm on March 6th
menus511 writes: Here in Iowa (Zone 5, with temp. dips to -20 F) I need some heat to keep my cold frame going in winter. My frame has plywood walls, and a plastic covered frame of 1x3s for the top. (Details in my article here: http://www.bhg.com/gardening/landscaping-projects/garden-structures/building-a-simple-cold-frame/) The cold frame sits on my deck, next to the back door. I used Styrofoam insulation on the sides and bottom, and made an insulating cover from old vinyl tablecloths and more Styrofoam. For heat, I use holiday lights -- three 100-bulb strings. With the insulated cover in place, the lights keep the temperature in the frame about 40 degrees above outside temperature at night. One point that's critical for newbys when it comes to cold frames: you need to learn how your frame reacts to changes in temperature, sunshine, wind, etc. And without an automatic venting system (or someone to check it regularly), it's very easy to fry a whole frameful of seedlings in about 30 minutes. Believe me, I've done it.
Posted: 8:40 am on March 6th
ChrisMcLaughlin writes: Ruth,

Sounds like an awesome little frame you had! I just LOVE having hale bales around - they are good for so many cool ideas.
Posted: 2:57 pm on March 5th
Ruth writes: Nice post, Chris. I haven't used a cold frame in a long time, but I might cobble something together this spring. Many years ago, though, we used to put hay bales wrapped in plastic around the foundation of our house to help insulate in winter. In spring, I used some of the bales to make a little cold frame. An old window frame became the top. I used this little structure mostly to harden off seedlings, and when I no longer needed it, I used the hay as mulch or just composted it.
Posted: 2:27 pm on March 5th
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