A root cellar is an easy, inexpensive and cool way to store root crops, winter squash and some other homegrown produce.

A root cellar was an essential part of every home in the days before fresh produce was available in supermarkets year-round. (The root cellar was also the spookiest spot in most old houses.) A root cellar is still an easy, inexpensive and a cool way to store root crops, winter squash and some other homegrown produce.

Even if you live in a newer house, you can still have a root cellar. The following are simple plans for transforming a corner of your basement into a root cellar, with a minimum of know-how and readily available materials.

Choose a damp spot. Most crops keep best in relatively high humidity. So build your root cellar in the dampest area of your basement (typically the sump pump is in the dampest corner).

Next to an exterior wall. You want, if possible, to build on a wall that's below grade (underground), because you want the greatest contact with outside soil temperature you can get. If you need to use a wall that's above grade, be sure it doesn't get too much sun. (Use north or shaded walls.)

Allow for ventilation
Without ventilation, your stored produce will spoil. To create good ventilation, you need to get two pipes through that outside wall—one at the highest point of the room. Both pipes should be about 3 inches in diameter. Try to pick a site that allows for this easily, such as one that includes a casement window or the like.

Your vents can be made of just about any pipe or ducting. Plastic (PVC)—3 inch—is durable and easy to work with, and the valves you'll need fit right into it. Cut a length of the plastic pipe to reach through the wall. Cut the end straight. Slide a closed blast gate (valve) onto the pipe until it fits snugly against the end of the pipe just tight enough to impart a slight resistance. Use 3 or 4 screws to secure the valve to the pipe.

Now cut pieces of pipe for the other vent. This one can go through the wall just about anywhere; just add an elbow and a length of pipe running down the inside so that it ends up about a foot from the floor. Add another blast gate in that pipe.

These two vents create a siphon. Cool air is more dense than warm air, and will collect in low spots. Anytime the air outside your root cellar is cooler than the air inside, the siphon will allow warm air to be drawn out and cool air to flow in. As outside temperatures fluctuate, you'll get almost continuous air change while keeping the temperature as low as possible.

Which brings us to the reason for the valves. If the temperature outside goes below freezing, you should close one of the valves to stop the siphon. You'll get some venting while keeping things from freezing. If the outside temperature goes way below freezing, you'll need to close both valves (at least partially).

Seal the wall around the pipes with aerosol insulating foam. This will fill in any gaps and cracks, and once it sets, does a good job of holding your pipes in place, too.

Source: http://www.organicgardening.com/learn-and-grow/building-root-cellar