Why do temperature and humidity matter?
Stored produce is still alive. It breathes, loses water and slowly ages. Cool temperatures slow those changes, and humid air limits shriveling. Warm or dry storage speeds spoilage and wilting, while very wet storage encourages rot and mold.
Different crops want somewhat different conditions. Roots and cabbages generally like cold and damp, while squash and onions prefer drier air, so a single space often needs zones.
Temperature in a cellar often changes slowly with the seasons. A cellar that is perfect in November may be too warm by March, so plan to use the most perishable food first.
How do I measure conditions in my cellar?
Place a thermometer and a hygrometer at the height where food is stored, away from the door and the vent. Check them regularly and write the readings down. Weather, season and the amount of food all change conditions, so one reading is rarely enough.
Keep a log through your first winter. It will show where the space runs cold, where it runs warm and when it needs adjusting.
If you see heavy condensation on walls, shelves or produce, record it. Condensation can mean warm air meeting cold surfaces and can point to a ventilation problem.
- Thermometer and hygrometer at storage height
- Check at the same time of day
- Record readings and weather
- Look for warm and cold spots
How do I adjust temperature?
Ventilation is the main tool. Opening vents on cool nights and closing them in the warmest part of the day lets cold air in and keeps heat out. Insulation, shade and the earth around the cellar help hold steady temperatures.
Keep the cellar from freezing. Frozen produce spoils quickly once it thaws, so watch forecasts and be ready to close vents or add insulation during hard cold.
Keep a small log of outdoor lows, too. Comparing cellar and outdoor temperature shows when opening a vent helps and when it hurts.
How do I raise or lower humidity?
Dry cellars can be dampened with damp burlap, pans of water or a bare earth floor kept slightly moist. Wet cellars need more airflow and possibly drainage work. Packing produce in damp sand, sawdust or leaves can also hold moisture around it.
Avoid standing water and persistent condensation, which feed mold. If water seeps in repeatedly, talk to a qualified contractor about drainage before storing food.
How should I arrange the food?
Keep air moving around crates and shelves, and do not stack produce in tight, deep piles. Store crops that give off gases apart from those that are sensitive to them, and keep strongly scented items away from others.
Check stored food often and remove anything soft or moldy right away. One rotting item can spoil what is near it.
Use wooden crates, slatted shelves or baskets rather than solid plastic bins, which trap moisture. Clean crates between seasons.
What safety points apply to a root cellar?
Underground spaces can have poor air, low oxygen or gases from decaying produce. Ventilate well, never work in a cellar alone for long stretches and take care with stairs, lighting and wiring. Electrical work needs a licensed electrician where rules require.
Rules about building or modifying a cellar, including excavation, permits and inspections, vary by state, county and town. Ask your local building and zoning office before you dig or alter a structure.
What should I do if the cellar is too warm or too wet?
A cellar that runs warm may need better insulation, shade, more ventilation at night or a deeper location. Storing food for a shorter time is also a fair adjustment, since it fits the space you actually have.
A cellar that is too wet may need better drainage, a vapor barrier or more airflow. Persistent water is a structural problem, and a qualified contractor or your local building office should look at it before you store food there.
If conditions cannot be fixed, move the most delicate food to a refrigerator or use it quickly. Your extension office can suggest options for your crops and climate.
Key takeaways
- Cool and humid storage slows aging in roots and cabbages.
- Measure temperature and humidity where food sits and keep a log.
- Use ventilation and moisture to adjust conditions, and prevent freezing.
- Give air room to move and remove spoiling food promptly.
- Ventilate for safety and ask your local office about building rules.
Sources and further reading
Last reviewed: November 12, 2026. Written by the Homestead & Small Farm Editorial Team. See our editorial policy.