A cold frame is a simple and useful project to construct. In it's simplest form a cold frame is just an unheated box or greenhouse built to provide minor insulation from the cold. It can be used to extend the growing season of your herbs and vegetables during the fall and early winter, it can be used to harden off your new young plants in spring and can be used as a place to grow seedlings and cuttings for spring propagation. A hinged or removable lid will protect your plants and can be opened to let in a bit of fresh air to prevent mildew or other humidity caused sickness, disease or rot.
For apartment dwellers or those with a small balcony or porch you can actually tarp in your whole space using the door to your home as the hinged roof to exchange moisture ridden air. The one pictured above is made with closet extension rods, vapor barrier from the hardware store and a bit of tape to hold the whole thing together. The extension rods get around the part of my lease that forbids construction of any type in my small apartment and actually extends my living space slightly into the cold of winter. It may not be the prettiest thing on the block but I still have fresh strawberries and herbs up until late january or early feburary. The heating costs here are also reduced by blocking the wind coming from that side of the building.
To construct a simple cold frame to use outdoors in your garden start by taking a walk around your neighbourhood. Chances are you will come across an old storm window or door that is being tossed into the trash. Even an old picture frame will work. If the glass is broken remove it carefully as not to cut yourself. While a glass top to your cold frame is ideal it is not necessary. Plastic wrap, vapor barrier, or even a clear trash bag may be substituted.
The next thing we need are 4 pieces of 2x4 or 2x2 to provide the corner supports for our box. Hammer these into the ground lining up under the corners of your top piece. For example you have a 2ft x 3ft window you found in the back alley; hammer the pieces of wood into the ground so that their outside dimensions are 2ft x 3ft.
Now, lay the top piece onto these posts to make sure that everything lines up. If all is flush then we are ready for the next step. Securing the hinges. Hopefully you managed to recycle a pair from somewhere but a pair from the hardware store at a cost of a dollar or two will be just fine. Attach the hinges to the posts and then to your top frame and you should have a simple box with no sides and a lifting top. You may add a catch to the front corner of the top attaching it to a front post if you desire.
Lastly cover the sides of your new cold frame with plastic wrap or better still wood if you have it thought plastic will work fine for our purposes.
A few tips for using your new cold frame are as follows:
1.Make sure that the frame is well drained to prevent flooding out of the roots in your new cold frame.
2.Orient your frame southward if you can to provide the most light exposure in winter and protection from the prevailing wintery winds.
3.Painting the interior white or lining it with foil will help increase the amount of light available to your plants.
4.On really cold nights insulate your cold frame with an old blanket or some straw. Pink builders foam is great if you can get it.
5.On those really nice spring days be sure to provide a bit of shade to your new seedlings to prevent sun scorch.
6.Lastly; try to place your cold frame near your watering source or close to your door as you will more likely take care of your plants in the winter if they are easy to access.