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This time of year, I’m getting ready for fall and winter, planting brassicas and garlic. But there’s a small piece of me that’s trying to hold on for another tomato, another pepper, maybe one more eggplant. And usually I can, because I have added infrastructure to my garden to extend the season before and after summer. Here’s what I do.
Build a cold frame
If you’re looking for a permanent situation, there is nothing better than a cold frame. This is a raised bed made of wood or steel, with a hard cover that you put on each winter made of either transparent plastic or glass. It insulates the bed so that rain, snow, wind and ice can’t get in, but because it is transparent, the sun can get through. The glass or plastic insulates the bed, too, so it stays much warmer than the surrounding area. Additionally, there must be a window to the cold frame that can be raised to let air in and out—this is essential because it acts like a vent. Although there are manual windows where you prop them open during the day and close them at night, most cold frames use an arm that automatically raises and lowers the window based on the temperature. The arm actually works via an internal piston that is surrounded by wax. The wax expands when heated, forcing the piston to activate the arm.
Cold frames are a simple build, which means you can easily make them custom to your raised bed. The articulating window arms can be bought on Amazon. You want to be sure you buy an arm rated for the weight of the window it is opening, but they’re otherwise easy to install with a few screws and a drill.
Of course, you can also buy cold frames, pre-built. You want to be sure they fit the size of your raised beds.
Cold frames you can purchase pre-built:
Every year I say I’ll build a cold frame, but while I find new ways to procrastinate, I make do with a popup greenhouse. These work a lot like popup tents, except that they are see-through and lower to the ground.
Every year I haul my popup out in the spring when my flower and vegetable starts outgrow my grow station and I need room for them. The popup goes on my patio, and all my baby plants go inside so they can soak in the sun.
In fall, the popup goes over one of my raised beds. Popup greenhouses have zippered doors and windows that need to be opened for ventilation, just like a cold frame—unfortunately, there’s no way to automate it (that I’ve found).
These popups are great because they buy me an extra month or two, but a word of cautionplastic is no match for winter winds. Unless that greenhouse is bolted down, it will take flight and you’ll spend your winter chasing it. The popup usually comes down before the first big windstorm, and folds up for next year. Even before a major windstorm, I would avoid tall, walk-in popup greenhouses. The ones that work are close to the ground, no more than 40 inches tall.
Pop up greenhouses worth looking at:
Low tunnels can spare plants from the cold
Farmers protect their garden rows using low tunnels—a miniature version of a greenhouse. A hoop is erected every few feet over the row, creating a tunnel. These hoops can be used to hang plastic in winter, shade cloth in summer, Agribon (an insulating fabric) any time, and screening fabric during the spring/summer to keep pests out, which you keep in place with hoop house clips.
Building low tunnels by hand in a raised bed is as simple as bending PVC over the bed. You can use pipe hangers screwed into the interior wall of your raised beds to hold the PVC in place. Having the hangers in place means you can pull the tunnels out if you’d like to, and put them back when you need them.
Depending on the season, you would add plastic, and possibly Agribon under the plastic, to create a cozy, insulated, and waterproof space for whatever is growing in the row under the tunnel.
Of course, you can purchase low tunnel kits, but you want to be careful to purchase a kit with sturdy hoops. Most kits are flimsy, which is why ultimately PVC is a better solution.
Low tunnel garden kits worth buying:
Hacks for keeping it toasty
You have to decide how far you’re willing to go to keep things temperate in your low tunnel, cold frame, or greenhouse. In the spring, I’m willing to do a lot to keep my baby plant starts happy, but in the fall, these structures are basically hospice, and you have to know when to let go.
In either case, I always keep a smart temperature reader in my greenhouses and cold frames. Depending on the season, I’ll have a small heater or fan on a smart plug in the space as well, and I have an automation (you can use Google, Alexa or Homekit to create one) to kick the device on when the temperature hits a certain threshold and kick it off when it falls within limits. So far, the two best temperature sensors are from Switchbot and Aqara, and you have to use mechanical heaters or fans for this to work.
