How deep a root cellar needs to be was one of the first questions I had when I was recently looking into installing one on my property. I did some extensive research on the subject and can give you a definitive answer.
How deep does a root cellar need to be? In order for temperatures to remain a stable 32º to 40ºF (0° to 4.5°C), a root cellar needs to be at least 10′ (3m) deep in most soils. However, in sandy, loamy, or dry soil, you often need to dig deeper.
Now let’s go through a few things that can affect the depth you need to dig as well as the overall success of your root cellar project. As you will see, there’s more to it than just choosing the right depth.
Building a Successful Root Cellar
Here are 3 major things that can affect the success of your root cellar:
1. How Soil Type Affects the Depth
Without getting too technical, the type of soil can greatly affect the depth at which you need to dig your cellar. The two things that control the depth that temperatures remain relatively constant are “heat capacity” and “thermal conductivity.”
To use a bit of common sense on how this works, looser sandier or loamy soils hold heat less well than firmer soils or clays. This makes sense, right? However, the biggest factor as to whether a soil holds its temperature well is how saturated it is. Wet soils are less affected by temperature fluctuations than dry soils are.
To put this in the simplest terms. If you happen to have loose, sandy, or loamy soils or if your soil is on the dryer side, then you might want to dig 12′ or a bit deeper when contructing your root cellar.
Although it will delay things, one thing you can do is dig a small hole to a depth of 10′, place a sensor at the bottom, and cover it. Monitor the temperature and humidity for a sustained period of time to find out if you need to go deeper.
The best way to monitor the temperature and humidity of the cellar is to use a Hygrometer. I recommend this indoor-outdoor Hygrometer (Click to see Amazon listing). It even allows you to track the humidity from afar, via remote sensors.
Humidity is another key factor for success with your root cellar. Attaining the right temperature does not good if the humidity is off.
Therefore, ensure you can control both temperature and humidity so you can adjust it accordingly. This will keep your produce in perfect condition as well as minimize the potential for airborne mold.
Regulating humidity in a root cellar can be done most easily using ventilation, which in itself is another important factor when digging a root cellar. It allows cold air into the cellar, by increasing ventilation during colder nights. You can shut it down during warmer days to keep things cool down below. Here is a helpful video showing one way to install ventilation:
2. Choose Your Dig Site Carefully
Planning your root cellar properly will set you up for success.
- Dig your root cellar somewhere with good drainage, which means that sandier soils work best. An elevated slope also helps keep water out of your root cellar. You want humidity in the air, not standing water which can cause your produce to rot.
- Avoid digging near large trees, as digging through roots will be more difficult, and the regrowth can later damage your root cellar. At worst, you can cause irreversible damage to the tree itself, including killing it.
- Build your cellar on the North or South side of a building or hill, so that the sun’s rays won’t have such an intense effect.
3. The Entrance Also Matters
Another way to ensure the temperature in your root cellar varies as little as possible is to keep the entrance small. The less the environment in your root cellar is exposed to the outside climate, the less the conditions will fluctuate.
This could be a narrow doorway that widens into a full room if you have chosen to dig an underground chamber. Or it could simply be a hole that has a narrow access at the top, with the entrance blocked off with a lid. That way, you can still reach into your root cellar, but the temperature stays as stable as possible.
Here are 4 other things you need to think about before starting any project.
1. Properly Store Your Produce
How you store the produce in your cellar is important as well. Here are a couple of things to think about:
*Prep the Produce Correctly
After just a little preparation, most root vegetables and many fruits can be stored in a root cellar. Make sure your vegetables are clean by brushing away dirt. It is better not to wash them, as excess moisture can cause rot. Handling your vegetables can also cause invisible bruises which can cause decomposition.
Some vegetables, most notably potatoes, pumpkins, and onions should be stored at warm temperature or room temperature for a few days before being placed in a root cellar. All fruits and vegetables emit ethylene gas, some more so than others. This causes other fruit and vegetables to spoil as well if they are in the vicinity. Therefore, wrapping fruit like apples and pears in paper is helpful to keep the surrounding produce fresh.
*Arrange Correctly and Rotate the Produce
When arranging your root cellar, ensure that produce is ideally around 3 to 8 cm (1 to 3 inches) away from walls, and that it is rotated regularly. This prevents mold.
Vegetables release heat as they slowly decompose, leading to more decomposition, especially in large quantities, and this varies depending on the type of vegetable. Therefore, rotating your root vegetables is important. To easily move vegetables or fruits around, I recommend keeping them in root storage bins, like this one found on Amazon.
Similarly, you need to regularly check for any decomposing or rotting produce and remove those immediately.
Taking these issues into consideration is important as a deep root cellar without ventilation and the ability to correctly store your vegetables may be of less use to you than a slightly more shallow one in which you can monitor temperature and humidity as well as the condition of your produce.
Humidity, on the other hand, is important to prevent your produce to lose moisture through evaporation which causes vegetables to wither.
2. Dig Safely
Digging a root cellar is a larger project than simply planting your potatoes, and it is important you ensure your own safety while doing so. This involves careful considering of the tools available to you, as well as the soil type, surrounding vegetation, groundwater levels and support structures needed to avoid collapse. Digging a root cellar is a manageable project for a home vegetable grower as long as you carefully plan your project before digging.
3. Beware of Building a False Root Cellar
While any cool space designed to keep root vegetables fresh for longer can be considered a root cellar, for anyone who wants to grow and store large amounts of potatoes or other root vegetables at home, a below-ground root cellar is most typically the best solution. These are made by digging a hole or underground chamber which stays at a stable, cool temperature.
You might have heard that the simplest “root cellars” are garbage cans that have been placed into a hole in the ground. However, this would not create a true root cellar since there is not sufficient depth for the temperature to remain stable.
While these simple “cellars” might work in some climates, consider your weather conditions. For example, if you want to shelter your vegetables from frost in winter when temperatures drop far below freezing, you will need a deeper, more sheltered root cellar than in warmer conditions.
4. Temperature Stability is Key
Root cellars were invented to keep a fairly stable temperature. In order for them to work correctly, the hole must be at around 10′ (3m) depth in typical soils. This will allow the temperature and humidity (needs to be 85%-90%) to remain stable. That temperature and humidity range will slow down the production of ethylene gas, impeding the onset of decomposition.
Keep in mind that warm temperatures are not the only problem. You also can’t let the cellar get too cold since frozen produce creates another set of problems. It causes damage to the cell structure and reduces longevity once defrosted again.
I hope I have given you all the information you need to intelligently choose the correct depth for your root cellar project.
If you want to learn more about root cellaring, check out this book called “Root Cellaring: Natural Cold Storage of Fruits & Vegetables” by Mike Bubel. It is a highly comprehensive guide and required reading for anyone building a root cellar.
What can you store in a root cellar? A root cellar is a useful way of keeping produce cool and therefore fresh for longer. While they are typically used to store root vegetables like potatoes, they can be used for storing all kinds of produce, as well as wine beer or other home-made alcoholic beverages.
Can you store meat in a root cellar? Since meat needs to be frozen and not just kept cool, a root cellar would not be a good place to store it. However, if the meat has been cured or preserved in some way, root cellar storage would be fine.