Cold Frames: Get a Jump on Spring
It’s that time of the year when a true gardener begins planting for the upcoming season. Spring never seems to arrive early enough, and with the limited number of actual growing days we have in Minnesota, cold frames are an excellent way to get a jump on spring. These systems allow you to move plants outdoors earlier in spring, and they also can be used to harden off indoor-grown seedlings or to start annuals from seed.
A cold frame is basically an outdoor box with a transparent cover which acts as a passive solar energy collector and reservoir. You can purchase or make your own cold frame from plywood and old window sashes or plastic. Most cold frames are 3 X 6 feet or made to fit the size of the window sashes or other materials which could be used for the cover.
How to Build Your Own Cold Frame:
1. Using rot-resistant wood, make the back wall 18-30 inches tall and the front slightly lower, about 12-24 inches. Cut side walls 3 feet long and with a slanted top to match the height of the front and back walls. The cold frame cover can be a wood frame covered with plastic or discarded windows.
2. Use 2 X 2’s for the corners. Make the posts longer than the sides if you want to use them to anchor the frame in place.
3. Face the front of the cold frame toward the south for maximum light and heat. Face the back of the cold frame north or against a building. Placing the cold frame next to a permanent structure will provide screening from the wind and the foundation will serve as a heat source. Another way to increase the heat within the cold frame is to paint the interior white and the exterior black.
If building a cold frame is out of the question, you can also use plastic sheeting. Row covers of polypropylene fabrics can be used to extend the growing season. The row cover fabrics help trap heat around the plants while allowing air, water and light through to the plants. Loosely drape the plastic over the plants being careful not to harm them. Anchor the sides, leaving enough slack in the fabric to allow for plant growth.
If you live in a colder climate, you can choose to extend your growing season by using a cold frame. A cold frame, with its natural light and warmth allows you to foster seedlings in early spring and keep veggies going through fall and even into winter.