How to Make a Cold Frame to Grow Vegetables or Flowers
By: Julie Day
A cold frame is like a mini-greenhouse that you can open during warm days.
A cold frame is a small, portable, unheated greenhouse that insulates tender plants from cold weather, allowing you to start your spring garden a few weeks early. It has a clear top that allows sunlight in to trap the heat.
In moderate climates, a cold frame can allow you to grow some herbs and vegetables year round! Cold frames are easy to build and use, here’s how to go about it.
Why Use a Cold Frame?
Cold frames are generally used for:
- Tender Plants: By covering tender plants with a cold frame, northern gardeners can enjoy plants that normally wouldn’t survive their winters. They can also be used as winter storage for semi-tender potted plants.
Start seedlings in a cold frame.
Vegetables to Start in a Cold Frame
You can grow or start most anything in a cold frame, but they’re especially useful for early spring vegetables like:
- Fingerling carrots
- Green onions
- Other root vegetables
Salad greens in a cold frame.
How to Build a Cold Frame
Cold frames are easy to build from recycled materials. They can be any size and shape, and they can be as fancy or as simple as you like. A cold frame consists of:
- Frame Box: Once you have your lid, you need to build a box for the lid to sit on. Pressure treated 2” thick lumber is a common choice, but you can also use recycled lumber and even stacks of bricks or cinder blocks.
An old window unit works great.
The dimensions of your cold frame will depend on the size of the lid, and it really can be as simple as sitting an old window over a wooden box. However, if you’re building one from scratch, useful features include:
- Easy Access: Limit the width of your cold frame to 3’ or less, so you can easily reach all the way to the back without having to step inside.
A simple cold frame design, vary length as needed.
Where to Locate a Cold Frame
Some people nestle a permanent cold frame against the south wall of their house or shed, while others build portable frames directly in the garden. Wherever you put your cold frame, the location should have:
- Insulation: You can rest the cold frame directly on the ground, or increase the insulating properties by burying several inches of the frame in the ground.
Cold Frame Tips
- Harden Plants: To prepare your seedlings for life outside, open the lid of your cold frame longer and longer each day, until you’ve finally removed it completely. Keep the lid handy in case of a cold snap!