The cool, moist and dark conditions of a root cellar make it the perfect place to keep many fruits and vegetables crisp and delicious for weeks — even months — of storage. And while there are myriad ways to store vegetables, our innovative root cellar plans show you how to build a root cellar by modifying a new, precast concrete septic tank. By following the plans, you’ll cut an entrance, install a door, add a pair of vent pipes and cover the tank with soil to bring an old-fashioned, walk-in cellar into your modern life.

Choose a Concrete Septic Tank

You’ll want to buy an unused septic tank for this root cellar design, but look for a deal to avoid paying full price. A percentage of all precast concrete septic tanks end up with small manufacturing defects that prohibit them from being used for sewage treatment. Suppliers sometimes offer discounts on these flawed tanks. As long as the tank is solid and sound, a chipped edge or a patchable hole won’t prevent it from being a root cellar. You won’t need the plastic fittings or effluent filter found inside most septic tanks, so ask the supplier to remove these before delivery.

Tank size is another detail you’ll need to consider when planning how to build a root cellar from a septic tank. The capacity of septic tanks is measured in gallons, with different models being taller or shorter. While you might be tempted to buy a 1,000- or 1,200-gallon tank because they’re common, you’ll get more food storage space and headroom with a tank that’s 1,500 gallons or larger. Standard 1,500-gallon tanks typically measure about 5 1/2 feet wide by 5 1/2 feet tall by 10 feet long, while a 2,500-gallon tank provides more than 6 feet of interior headroom. Don’t choose a low-profile tank because it will be much too short to work in. Prices for new, undamaged 1,500-gallon tanks start at about $1,100, and 2,500-gallon models can be found for as low as $1,600. Discounts for damaged tanks may be as much as 50 percent.

Most septic tanks have an internal partition that must be opened or removed to build from these root cellar plans. Try to find a tank without a partition, or ask your supplier to remove it before delivery. You can also punch through the partition yourself as part of the doorway-cutting process.