The Biggest Problem With Cold Frames
So you want to try cold frame gardening. Great! You’re in the right place. Let me see if I can scare you into choosing the right cold frame. Here’s the first question. Do you have a dog?
See, the biggest problem with a winter harvest is the day-to-day routine required to keep a cold frame running. You must vent your cold frame during warm, sunny spells, or you’ll burn, harm and even kill the plants inside. It’s as simple as that. Too much sunshine in an enclosed space means spiking temperatures and tough days for the plants inside your cold frame.
That’s why I asked about Man’s Best Friend. Getting a winter harvest out of a cold frame is kind of like having a dog. If you’ve got a dog, you get to look forward to a nice walk every single morning and every single night. Every single ice storm morning and every single wind-and-rain night! And if you get busy and miss a walk – well, you know what happens if you miss taking your dog for a walk! A big mess.
Conventional cold frames are the same way – every day in the fall and spring, when the weather is topsy-turvy, you’re going to have to think about the temperature and the expected sunshine and plan on taking a walk. You have to be ready to get out to your cold frame if the cloud cover breaks and the sun starts to shine. (And doesn’t it seem to shine hotter and hotter every year?) A non-automatically-vented cold frame can rapidly heat up and damage the plants inside, even if the air temperature outside is in the 40’s or 50’s.
Now, maybe you’re home during the day and can remember to tend the frame. Or maybe your children or spouse would be able to remember to vent the frame during the day without being asked – mine certainly wouldn’t! The best feature of our frame – and the one that we worked for a long time to get right – is the self-opening feature.
There’s a material inside the two cylinders in the front of the cold frame. That material is frozen into crystalline form when it’s under 50 degrees. As the temperature warms up, those crystals turn into liquid and expand. A lot. We apply those expansive forces to a lever system that’s attached to the top light. That expansion action automatically opens the frame. When the liquid cools back down to 50 degrees, springs pull back against the cylinder, causing it to compress. The lid of the cold frame closes and the frosty night air is kept out.
Don’t get me wrong: even our cold frame isn’t going to provide adequate venting for those full-on sunshiney, mid- and late-spring days when it gets genuinely hot. (Remember when your peonies on the south side of your house bloomed six weeks early last year? A cold frame on the south side of your house would have been way too hot during the day for many of those days.) On those warm, late-season days when there’s no chance of frost, you’ll need to completely remove the lid from your cold frame. (It’s easy to do – unlatch the front retainers and slide the lid along the hinge.) Remove the lid during the day and, if necessary, replace it in the evening. It’s as easy as pie.
It’s easy to tell when it’s going to get hot. It’s the transitional days – here in Chicago that means anything from the first of October through early November – when the temperature might suddenly drop to freezing or might suddenly spike to 60 sunshiney degrees – that our self-regulating cold frame really comes into its own. With the cylinders, you won’t have to worry about the temperature inside the frame.
Did I scare you? I hope so. The Common Sense Cold Frame is the easiest and simplest way to get great later-season and early-season results for your garden. Thanks for reading!
Russell Potterfield
Founder
Carnival Gardens