Building a Cold Frame with Dankohzee

In my home state of Maine, the grow season happens fast. The slightest hesitation or procrastination could cost you an entire crop. Plants must be ready to go in the ground the moment the last frost has thawed if a bountiful crop is to be had before winter sets in. But it is not just the autumn freeze that can spell disaster. Many a Mainer has miscalculated the critical last frost date and lost his crop to an unexpected spring freeze. I remember losing three flats of some cherished Kentucky bagseed seedlings that I had waited forever to be able to grow. It was a 75 degree day and had been 50+ for a week. Then all of a sudden the mercury dipped and that was all she wrote for my beloved Kentucky crop.

These days Dank doesn't take any chances. While I am not quite handy enough to attach a greenhouse to my home and grow pot in January, I do have a working familiarity with every Yankee gardener's best friend: The cold frame.

Cold frames can be used to start vegetables and herbs in the spring before they can be sown into the soil. Additionally cold frames can be used in the fall and winter to extend the growing season for hardier crops. I've kept seedlings in cold frames on nights that dipped to the upper teens without any problems. For nights that get colder than that, a blanket or piece of heavy burlap can be used to cover the frame, adding additional warmth. Some people even place votive candles inside to raise the temps a few critical degrees.

A typical cold frame is a box constructed of wood with the front of the box being lower than the back. The top of the cold frames is covered with plastic or glass and can be opened on sunny and warm days to increase ventilation, and closed again at night when the temperature begins to drop. You don't have to have any special carpentry skills to construct a cold frame, and chances are you have many--if not all of the supplies you will need to build one.

The first thing you will need, and perhaps most difficult to find will be a window. I like to use wood framed windows because they can be repaired easily and can be found almost anywhere anyone is remodeling a house. Look in the dumpster, there's probably a dozen in there. For the cold frame I built today (which I will place amidst some grasses and brush out back and use to start this year's crop) I chose a fairly large window. This one is about five feet tall and has a lot of glass without much wood obstructing it. It's in bad shape though.



The first thing I usually do is give it a rough scraping. This one is going to live in the bush, so It's not going to be pretty. Next I'll re-caulk the window itself. I don't necessarily care if a little water drips through the window, but if water is flowing through it, it won't last long before it falls apart. It's best to get it relatively water tight.



Next I reinforce the window top in all the places where pieces of wood meet. This will help hold the window together. Remember the window is also a lid and lids take beatings. You'll want a strong lid/window. Here's a pic of the sort of metal braces I use for the top (much later in the project after attaching the hinges). The L shaped brace is good for corners, and I used a couple of straight braces to reinforce the piece of wood that goes down the middle of the glass.

Once you have a rehabilitated window, the rest is easy. This can be as simple or as fancy as you want it to be. In fact, one simple way of building the box doesn't require building a box at all. You could dig a shelf into the side of an appropriately slanted hill and cover it with the window if you wanted to. Or you can build box like I did.




Let the size of the window determine the length and width of your box. A common size for the height of the box is 12 inches in front and 24 in back, but this isn't written in stone. What's important, however, is that you have one inch of rise per 12 inches of window, front to back. In other words, I'm going to put this window on my box. It's 36 inches front side to back.



This means that the back side of the box must be 3 inches higher than the the front. This ratio will give you the best light penetration and consequently the most even growth. But I've seen cold frames that were completely flat, they just didn't work as good.

Once your box is built you may want to put some hinges on it. You don't have to though. Many people just rest the top on. I like hinges on mine so I used them, and I also put on a handle for easy lifting of the lid, and hand-holds on the ends for easy lifting of the box itself when I place it in the weeds tomorrow.



Then I devised a prop-stick to hold the lid up. This one folds into the box, but you can just use a stick if you want, stoner.




Then I painted the interior white and the exterior black. White for reflectivity, and black because I like to see how early and late I can use mine. I don't think you need to paint it a dark color though.




Location Cold frames should always be located on well-drained soil, free from flooding during heavy rain. A location with a southern exposure and adequate wind protection on the north and west is ideal.




Use

Once the frame is built and a suitable site chosen for it, a couple of decisions have to be made. To bury or not to bury the frame partially, and whether to grow in pots/flats, or directly in the ground. If the bed is partially buried it will stay warmer. If it cannot be partially buried it can be set on top of the ground or placed on bricks. Sometimes I will make a brick base--just one row of bricks buried flush with the ground that the frame can rest on. Part of the brick is on the inside of the frame and part on the outside, sucking up the sun and transferring the heat inside. The bricks stay warm well into the night. If seedling will be grown directly in the ground, the area that will be within the cold frame must be prepared in much the same way as one would prepare a hole for an outdoor grow, except this earth will be prepared with seedlings in mind--not full sized plants. Once the soil is loosened and amended and ready for planting, the frame can be placed on top of it and seeds can be sown.

A soil temperature of 70 to 75 degrees F is ideal for germination of most seeds. Following germination, adjust the temperature to suit the particular plant. Cool-season crops such as lettuce, cabbage and cauliflower require an air temperature during the day of 60 to 65 degrees F. Warm-season crops such as tomatoes, peppers, and melons require an air temperature of 65 to 75 degrees F. Night temperatures are usually 5 to 10 degrees F lower than day air temperatures. If the air temperature in the bed goes above 85 degrees F, ventilation will be necessary. The beds usually require ventilation on all mild, sunny days.

Well I hope this get you all growing in the great outdoors right away--fuck waitin! This thread will be a work in progress. At the end of the season I will take this cold frame and turn it into an electric hot bed, something I have been wanting to try for quite some time.

By the way, in an effort to save time, I have pilfered certain sentences of this post from the internet. You do it too so don't sit there and say you don't. Stop judging me.

 

On a 62 degree day it is 90 in the box with the lid down--without any bricks at all. I set this one down on thick black plastic and trimmed the excess off--no bricks as it is a guerrilla cold frame to an extent (not really but sort of). The plastic will keep the weeds from going crazy on the inside of the frame.

Hey thanks firstimah. Just about any gardener worth his salt has used one of these at one time or another. They're great tools.

Haha! That would be nice.

That's a great example of the ubiquity and simplicity of the cold frame. In Spain a light cover such as that is probably more than sufficient.

Thanks Pork. I think how-to threads make a forum community a much more enriching place to visit. I just wish I had more knowledge to share. Being a citizen of the city can be humbling sometimes. I'm more of a redneck grower than anything--I would probably fall asleep in a botany class!

Hey one of these might work great for that! depending on what your setup is you may even be able to put alittle flourescent growlight inside that could stay on over night. Might help them perform a little better.

 

By the way Cantharis, I love your watering can. What brand is it?

 

Here's a pic that may help for visualization purposes:

 

Wow. This thing is still on?

 

That would make it a "hot bed."

 

Whoa!! Easy killer. I was simply adding some info to what I thought was a quality post. Cool yer britches.