A simple cold frame is an easy, economical way to get more out of your garden.
You might know that I built a small greenhouse this fall. Unfortunately by the time I finished it in early November it was pretty late to get started – I have a few things going in there now, but I’ve not really been able to use it to full advantage. Being able to enjoy the sunshine while I’ve worked in there out of the cold has been nice. But the truth is that so far this cold frame has been at least as productive as the greenhouse.
While I built my greenhouse on the cheap ($50 out of pocket) building this cold frame actually cost nothing – 100 percent recycled materials. Not only that, but the design is so simple that anyone should be able to build one in an hour or two once you scrounge up the few things that you need. The glass for my cold frame came from a sliding glass door – it started life as double pane glass, but a lawnmower thrown rock converted it to single pane – it works great. You could use just about any piece of glass – as long as it isn’t tinted or too large or small - just build the wooden parts to fit the glass pane that you have. I must say that it is very convenient that mine has a frame around it instead of being just a plain piece of glass, but don’t let that stop you if that’s what you come up with.
The principle is about the same for a cold frame as it is for an unheated greenhouse – inside it’s like your plants are spending the winter 2-300 miles further south – maybe better. They’re protected from wind, cold rain, low humidity, snow, and many frosts. It’s not like they’re in the tropics, it’s just that winter is a lot milder inside of a cold frame. One particularly warm day at the beginning of January it got up to 87 degrees (F) in mine but even though that sounds really hot I don’t think that it’s the same as an 87 degree day in August – the ground is cool and there just isn’t so much radiant energy. Anyway, it didn’t seem to bother the lettuce and spinach that was growing in there. You can probably treat it like it’s at least one zone warmer – Instead of planting arugula in March you can plant it in January – and you also get an extra month in the fall.
Wouldn’t it be better if the glass was at a steeper angle, the soil was in an insulated chamber, everything was weather stripped, the inside was a nice reflective white, and it had an automatic vent opener? Maybe, but it works really well just like this. The truth is that if it was all that complicated or expensive I probably wouldn’t have built it to begin with. Also the fact that it’s a bit leaky probably helps to keep it from overheating and might be more important than keeping out every possible draft.
Isn’t that plain spruce lumber and chip board going to rot? It sure will, but 1) I try to avoid using treated lumber in the garden if at all possible 2) Rot resistant wood like cedar and redwood are uber expensive 3) Nothing lasts forever 4) It was FREE – scraps, culls, and reclaimed materials. When it does rot I’ll replace it with more scrap/recycled material.
Wouldn’t a plastic tunnel work just as well – maybe, but it’s a lot more trouble to open one of those to do anything – the convenience of being able to just tip the glass up means you’re more likely to take care, and pick food out of it. Then again if a plastic tunnel is what you’re up for then by all means go for it – it will get the job done.
Because of the simple design when the weather warms up I can move the whole thing out of the way, or I might move it over some strawberries and replace the glass with a screen to keep birds out. It would also be useful like that for keeping vine borer moths off of young squash plants.
As you can see there aren’t any hinges. The glass just sits on top, and the piece of wood where the hinge would be keeps it from sliding off when the lid is propped open. The 2×4 just elevates the back so that rain drains off - The glass comes off to make it easier to work in – The whole thing just sits on top of the ground – I pushed a bit of soil around the bottom where needed to fill any gaps.
Where to put your cold frame – In a place that gets as much sun as possible, and remember that the sun will be lower in January than it is in September. I set this one right over an existing raised bed that already had very good soil, and if you have a choice try to put it close to the kitchen so that it’s handy to pick a fresh salad for supper.