Cold Frames

Welcome back, gardening friends! I hope you had a wonderful holiday season and a happy new year.

The deep freeze that has hit most of the eastern half of the United States has just found its way to me. Fortunately, over the long holiday break, I took advantage of some warmish weather to repair my cold frame, which took a bit of a beating during the recent home renovation.

A cold frame is a simple enclosure with a clear or translucent roof that is used to shelter plants from cold or otherwise inclement weather. It is similar to a greenhouse, only generally less grand, and specifically, unheated. It can sit low to the ground or even be dug into the ground. It can shelter pots or can be planted directly, depending on the user’s needs.

I built mine out of recycled materials three years ago. It is a simple wooden box, measuring 8 feet long by 3 feet wide, and slopes from 20 inches tall at the back to 15 inches in the front.

Because the area where it is located contains the main electricity line to the house, the box sits on the surface, atop of a thick layer of gravel. In a colder climate, I might dig the cold frame into the ground, but it seldom stays very cold here for long.

The frame windows are upcycled window sashes from the Habitat for Humanity ReStore.

In the past, I lined the perimeter of the frames with foam weatherstripping, which does a good job of keeping out the cold air. However, it becomes brittle after a season and must be replaced annually.

The white-painted interior reflects light to the plants inside. The cold frame faces south, but tall trees to the southeast block some sun, even in the winter. (I’ll paint the outside to match the house when the weather warms up.) The cold frame does an excellent job of sheltering  tender plants, like my salad bowl garden. It also keeps my worm composting bin frost-free, allowing the worms to continue their good work, albeit more slowly, in the coldest months.

One of the window sashes was damaged during the renovation and must be replaced. I have been slow to fix it because its sorry state has spared me from having to vent the box during the warmest part of the day. I cannot replace the window today, but with overnight temperatures expected in the single digits Fahrenheit (that’s very cold for here), I need to make some arrangements to compensate for the heat loss the broken window allows.

First, I’ve crowded my plants together tightly in the section furthest away from the broken window. Reducing the gaps where frigid air can circulate will help the plants survive. I’m moving a few of my winter sowing seed pans and cuttings into the frame as extra insurance, though that does go against the philosophy of winter sowing.

Next, I took a few old shopping bags from my shed, filled them with dry leaves, and tied the handles closed. I tucked these in amongst the plants inside the frame. These will act as makeshift insulation batts, sheltering the plants from any drafts.

Mother Nature’s insulation, trapped in Nature’s nemesis, the plastic shopping bag.I’ve tucked the bagged leaves in gaps around the pots to reduce drafts.

Third, I cut a double-thickness section of 3.5-mil translucent plastic sheeting to fit the window frame and stapled it into place, to help compensate for the broken panes of glass.

Finally, below the window sashes but above the plants, I added a layer of that same 3.5 mil plastic sheeting and some cardboard before it goes to the recycling. This should stop most of the cold from penetrating the broken window.

I know my northern neighbors are coping with much worse weather, and my thoughts are with you all. Stay warm and safe!