Want to build a simple cold frame? This one’s perfect for hardening off tender plants that you’ve overwintered indoors. And it’s easy to build and store! Here’s how: Start with polyethylene round bubble basement window well covers from the home improvement store.
Build a base of bricks against the foundation of your home, where the home’s heat can warm the frame, and put the upside-down cover on top. Then put your plants inside to transition them.
When you set up a cold frame, face it toward the south and irrigate with water close to the temperature of the soil to keep a warm environment. To begin, only place the plants in the frame for 4 hours a day, and slowly increase over time.