Manage a cellar by matching each food to its own temperature and humidity: root vegetables keep best at 0-4 degrees C and 90-95 percent humidity, potatoes at 4-7 degrees C and 85-90 percent, and onions and garlic at 0-4 degrees C and 60-70 percent. Raise humidity by setting pans of water on the floor, lower it by opening the ventilation wider, and keep onions in a separate, drier place from the other produce.
Part of Ice Houses and Cold Storage
Temperature and humidity control in a cellar means holding the air within the range each stored food needs, using only vents, water pans and the choice of where to put each crop.
Foods Disagree About Humidity More Than About Temperature
A cellar is one volume of air, but the foods in it want different conditions. The ice-houses parent article lists them. Read down the humidity column and the conflict shows: root vegetables and cabbage want 90-95 percent, potatoes 85-90, apples 80-90, while onions, garlic and cured meats want 60-70. The gap between onions at 60-70 and carrots at 90-95 is at least 20 percentage points (90 - 70), so these cannot share still air.
Temperature is simpler but still varies. Most items want 0-4 degrees C, potatoes want 4-7 degrees C (colder potatoes turn their starch to sugar), and the parent article’s lead range of 2-10 degrees C for a whole cellar is wider than most foods want. In summer a cellar may reach the upper end of that range, which is warmer than most of the table. The cure is to use the coolest part of the cellar for the crops that need it.
What You Need
- Thermometers — a minimum-maximum thermometer is best; two at different heights show how the cellar layers. A thermometer you can read without entering is safer.
- A way to read humidity — two thermometers side by side, one with its bulb wrapped in a wet cloth. The wet one reads lower, and the drier the air, the bigger the difference. Without a conversion table this gives you a trend, not a percentage; watch for rising and falling differences.
- Pans of water — for adding humidity.
- Vent controls — plugs or sliding covers on the pipes. See Cellar Construction.
- Dividers — to make drier and wetter zones.
Method: Control The Conditions
Step 1: Map the cellar. Read temperatures at the floor and the ceiling. Cold air sits low, so the floor is coolest. Plan the cold-loving crops there.
Step 2: Group by humidity. Put root vegetables and cabbage together, potatoes in a darker, slightly warmer spot, and onions, garlic and cured meats in a separate dry corner or a separate room.
Step 3: Raise humidity with water. Set pans of water on the floor. Wet sand around roots also helps.
Step 4: Lower humidity with air. Open the ventilation wider. Remember that it works best when outside air is cool and dry.
Step 5: Watch for condensation and mould. Water on walls or a musty smell means too much humidity or too little air.
Step 6: Check on a schedule. Read the thermometers weekly. Remove any rotting item at once, since one rotten item spoils its neighbours.
Worked Example: Can Potatoes And Carrots Share A Bin?
From the parent article’s table:
- Carrots: 0-4 degrees C, 90-95 percent humidity.
- Potatoes: 4-7 degrees C, 85-90 percent humidity.
The temperature ranges touch only at 4 degrees C. The humidity ranges do not overlap: the lowest carrot figure is 90 and the highest potato figure is 90, so the only shared value is exactly 90 percent, with no margin. At a shared 4 degrees C and 90 percent both are at the edge of their range, so each would keep for less than its best time. Better to separate them, with carrots on the cold floor level and potatoes higher up.
Common Mistakes
- One setting for the whole cellar — some foods will always be wrong.
- Mixing onions with other produce — they need drier air, and the parent article warns that they emit gases that speed spoilage in other crops.
- Mixing apples with vegetables — ripening fruit gives off ethylene gas, which speeds spoilage; keep fruit apart.
- No ventilation — humidity builds to the point of mould.
- Never reading the thermometer — a cellar that creeps above range in summer spoils the crop unseen.
Safety
Air checks do not replace a safe entry
Thermometers and hygrometers say nothing about the oxygen or carbon dioxide at the floor. Before anyone enters a closed cellar, ventilate it to the floor, tie a line to the person going in and keep an attendant at the top. Never test the air with a flame. See Cellar Construction.
What’s Next
- Learn next: What to Store — which foods go where
- Combine with: Root Cellars — the broader principles of cellar storage