Building a Cold Frame

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I’m Jake Klingensmith with the Ploughshare Institute. Today I want to be talking about a cold frame and show you how to build one. The nice thing about cold frames is they will extend your growing season. In the late fall when you’re planting lettuce, cabbage, broccoli, and most of your greens, you can extend your growing season by putting a cold frame over them.

First thing we need to do is talk about the tools here. OK, here we have a sharp saw, a drill, you’ll need a good pencil, a counter sink, 11/64 drill bit, tape measure, and some squares. This is all you’ll need to put together this cold frame. Next we’ll talk about the materials you’ll need. You’ll need two 1 by 10, 8 feet long boards.

Here I’m using pine, but you can use cedar or redwood. You’ll want to stay away from treated wood, they tend to leech the preservatives into the soil. You’ll need some two inch screws, and also some inch and a quarter screws. You’ll need a piece of Plexiglas. It’s 1/4 inch thick, 2 feet wide by 4 feet long. You’ll also want a handle to open the Plexiglas lid.

All right, now we’re ready to start cutting out some materials here. First thing you’ll want to do is square the end of your boards. It’s very important to get a square end. That’ll start us off on the right track. Now with this sharp saw, I’ll cut it out. All right, next thing we want to do is cut out the end of the cold frame here. The ends are 24 and 1/4. Again, we’ll want to use our square to make sure all our cuts are square.

OK, now we want to cut out our sides. They’re going to be 50 and 1/4 inches. OK, now I’m using 1 inch rough cut lumber here. Your typical lumber from a lumber store is going to be 3/4 of an inch. So if you get 3/4 inch stock, you’re going to want to cut it at 49 and 3/4 instead of 50 and 1/4. So depending on what material you use, if it’s 1 inch rough cut, you’ll cut it at 50 and 1/4.

Now, if you’re going to use your standard 3/4 inch, you’ll definitely want to cut it at 49 and 3/4. But I’m using one inch material here, so I’ll cut it at 50 and 1/4. Your short pieces are going to stay 24 and 1/4 regardless of what thickness you use. OK, now we’ve got our two sides, which are 50 and 1/4 inches long, and our two ends which are 24 and 1/4.

The next thing we need to do is cut out some stops for the Plexiglas to rest on. I want these stops to be 1 inch by 3/4 of an inch. So I’ve got my 1 inch board already, and I will mark it at 3/4 of an inch. Both ends. I’m going to cut out some strips, so I want to mark it. These long strips. With this handy saw, I’ve got my cross cut here and also my rip in one saw. So I’m going to use the rougher teeth, which is for ripping.

One tip on cutting long cuts like this is to keep your saw at an angle. It’ll help you stay on your line. OK, you’ll need to cut two out of the 24 inches, and you also need to cut two more at 48 inches. Now that we’ve got our glass stops cut, we’re ready to start assembling. But before we actually put it together, with pine, or cedar, or even redwood, it’s very important that you pre-drill the ends so that the wood doesn’t split.

We’ll come over here and get out our counter sink. OK, on the short stops, I’m going to put three holes in them, one in the middle one on either end. And on the longer stops, I’ll put five holes. It’s not too important that you measure them out. Just generally space them apart. I’ll put one in the middle and one evenly spaced between the two end ones.

OK, now that we’ve got all our holes pre-drilled here, we’ll also want to pre-drill the sideboards. You’ll want to pre-drill about 1/2 and inch from the edge. And I put four screws in the end, so I want to pre-drill four evenly spaced. You want to do it on both ends of these sideboards here. Next, we’ll want to cut out our prop stick. It’s cut out of a 1 by 2, and it’s 10 inches long. This keeps the bed from getting too hot inside.

So I’m going to cut it off here at 10 inches. Next, I want to cut in little triangles where it’s going to hold the glass. I’ll cut three of them. I’ll start the first one at 2 and 1/2 inches, the second one at 5 inches, the next one at 7 and 1/2. I’ll use my square to mark an inch and a quarter down the line. There you go, inch and a quarter.

Then I’ll use the 45 degree side of the square to make a second line, which there I cut out my little triangle. OK, now I want to cut down on those lines. Get the 45 degree side. And now the last one. Now, you want to use some caution because this one’s going to be a little bit harder to cut. Don’t cut your hand on this one.

OK, now here you go. This is for like on the cooler days, when the sun’s shining through, you’ll just put the glass right here. Then as it gets hotter, you’ll extend the glass up to here. And this will sit on the edge of the cold frame and the class will come, depending on how hot it is, on each one of these. This is kind of like your low tech thermostat.

All right, now we’re ready to start putting all this together. We will start by clearing off the bench. Need our Phillips bit in the drill, and we’re going to use the 2 inch screws to put this whole thing together. One of the easy things to do is to put all your screws in these holes before you get started. It saves you dropping your screws all over the ground.

Then we’ll take our sides and square it up with the end. Switch to the other side. OK, here we go. OK, now we’re ready to put the last piece on. Put this here. Again, make sure these are nice and flush. It’s always easier to put your screws in the holes first. Now we’re ready to finish the last end here. Bringing these boards flush with each other.

OK, well, there’s your basic box. Now we need to put in the glass stops. These stops here are what’s going to hold the glass in place. We’ll want to measure 1/2 an inch from the top of the cold frame down. Here we are. We’ll make three marks, one in the middle and one on either end. And then we’ll start with one of the long ones. Put right on those marks.

OK, now it’s important to remember that you don’t want to use the 2 inch screws here. You’ll want to use those inch and 1/4 screws. The 2 inch screws will end up popping through, and that’ll be a problem. Keep it on the line. Here we’ll turn the box over and do the same thing on the other side. Next you want to turn it on its end. OK, there we go. Now we’re ready to start putting the glass in.

Before we do that, we’re going to want to put on our handle here. It’s a 3 inch handle you can get at most of your hardware stores. We’ll need to find the center of the glass. 48 inch piece of glass, it’s going to write at 24 inches. We’ll want to measure and inch and 1/2 from either side of that center mark. And I’ll want to do 2 inches from the edge.

OK, now with an 11/64 drill bit, we’re going to drill these holes. Don’t rush it. It’s important not to rush it on trying to get the hole drilled, because the Plexiglas will crack. Just let it smoothly set into it. We’ll switch back over to our Phillips bit here. Now we’ll just use some of the inch and 1/4 screws here. You want to be very careful with this Plexiglas. It cracks very easily. Don’t tighten your screws too tight.

OK, now that we’ve got our handle on, ready to put this glass right in. Here we go. Now let’s take this to the garden and put some plants in it. Now we can plant something in this. We can either start our seedlings and flats, or we can plant directly in the bed. Here I’ve got some seedlings, and I need to keep them warm on this chilly day. I’ll just put them right in here.

I also got some jalapenos here that are about to sprout. This is going to be a perfect place to start them. Now, it would be a good idea to put a thermometer inside. And you want to keep the temperatures at about 75 to 80 degrees. So, just throughout the day you’ll want to look inside and make sure that’s not getting too warm.

Currently it’s in the mid ’30s, and after 10 minutes of having this cold frame here, it’s already 63 degrees in there. So it’s very important to keep a good eye on the temperature inside the cold frame on a bright, sunny day. And as the temperature gets around 80, then just go ahead and put your little prop stick in there. that’ll start letting some of that extra heat out.

OK, well, here’s your cold frame. Very simple to make, easy to manage. A great place to start seedlings in the early spring. You can have lettuce throughout most of the cold months. This will keep it warm. Biggest thing is to make sure it doesn’t get too hot. They’re a great place to grow greens all winter.

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