# How to Build a Root Cellar That Holds 32 to 40°F · Larder & Well > Source: https://larderandwell.cc/homestead/how-to-build-a-root-cellar Homestead skills ## Building a Root Cellar Earth holds cold and damp better than any appliance. Here is how to build a cellar that keeps a fall harvest through winter with no power at all. By Ruth Calloway, November 10, 2026 A root cellar works when it holds most of its space between 32 and 40 degrees Fahrenheit with the air at 85 to 95 percent humidity, and has a low vent to let cold air in and a high one to let warm, damp air out. Build it into the ground on the coldest side of your property, keep it dark, and potatoes, carrots, beets, cabbage and apples will keep for months without a watt of electricity. That makes the cellar the bridge between the garden and the pantry. Canning and drying take fuel, jars, time and tested recipes. A cellar takes a hole, some lumber and a season of paying attention, and then it stores whole food with no processing at all. Farm families leaned on cellars long before rural electrification, and the physics that made them work have not changed. ### Root cellar storage temperature and humidity A carrot pulled in October is still living tissue: it breathes, burns its own sugars and loses water through the skin. Kansas State's storage bulletin, reprinted by [University of Maine Cooperative Extension](https://extension.umaine.edu/publications/4135e/), puts the target plainly: fresh produce needs temperatures of 32 to 55 degrees and relative humidity of 80 to 95 percent to slow that breathing and the water loss that comes with it. Cold slows the clock. Damp air keeps roots from shriveling. Both ends of the temperature range can hurt you. Below 32 degrees most produce freezes, and the same bulletin notes that potatoes, sweet potatoes and peppers are among the crops a single freeze can ruin. At the warm end, the bulletin explains, produce breathes faster and deteriorates faster, and stored roots start to sprout. The goal for the main room is the narrow band just above freezing, held as steady as the ground lets you. Do not judge humidity by eye. The bulletin's advice is to read it with a hygrometer rather than from how the produce looks, because by the time carrots go limp the water is already gone. A cheap digital hygrometer and a maximum/minimum thermometer, hung at bin height, tell you more in a week than a season of guessing. ### What keeps, and for how long One room cannot suit every crop. The K-State table sorts produce into roughly three climates: cold and wet for roots and cabbage, cold and drier for onions and garlic, and cool and dry for winter squash. Sweet potatoes are the odd one out, wanting 55 to 60 degrees, which is closer to a spare bedroom than a cellar. These are the bulletin's figures for the common storage crops. | Crop | °F | Humidity | Months | | -------- | ----- | -------- | ------ | | Potatoes | 38–40 | 90–95% | 5–10 | | Carrots | 32 | 98–100% | 7–9 | | Beets | 32 | 98–100% | 4–6 | | Parsnips | 32 | 98–100% | 4–6 | | Cabbage | 32 | 98–100% | 5–6 | | Apples | 30–40 | 90–95% | 1–12 | | Onions | 32 | 65–70% | 1–8 | | Garlic | 32 | 65–70% | 6–7 | | Squash | 50 | 50–70% | 1–6 | The months are what a commercial store gets at steady conditions. A backyard cellar that drifts a few degrees will land at the short end, which is still most of a winter. The cabbage line is for late, fall-harvested heads, and the potato line is for the late crop dug after the vines die. A home cellar can still serve all three climates. Cold air sinks, so the floor is the coldest, dampest spot and the ceiling the warmest and driest. Put roots and potatoes low, onions and garlic on high shelves near the exhaust vent, and carry the squash up to a cool closet or an unheated upstairs room in the house, where the air is drier. ### Pick the type that fits your ground There are three classic ways to put a room in the earth, and the Bubels' book _Root Cellaring_, summarized on [Wikipedia's root cellar page](https://en.wikipedia.org/wiki/Root%5Fcellar), describes all of them. Which one you build depends more on your soil and slope than on taste. **The hillside cellar.** Dig straight into a bank, wall the cut with stone, block or timber, roof it and pile the spoil back on top. Digging sideways moves less dirt than digging down, and rain drains away from the door by itself. If you have a north- or east-facing slope, this is the easiest cellar to build well. **The dug-in cellar under a shed.** On flat ground you go down and enter through a hatch, often inside a small shed that adds a buffer of still air between the cellar and the winter. It needs good drainage around and under it, because water runs into a hole on flat land and has nowhere to go. **The mounded cellar.** Where rock or a high water table stops the shovel, build the room at grade and bury it under earth, rock and sod. It needs more fill and a heavier roof, but it skips the hardest excavation. A fourth option needs no new structure at all. In a house with an unheated or partly heated basement, wall off a corner on the north side, insulate the new partition and ceiling from the warm house, and bring outside air in through a basement window. You lose the earth on top, but you gain a cellar you reach in slippers. For a few bushels, the old shortcuts still work too: roots packed in damp sand in a buried trash can, or a straw-lined clamp in the garden. Newfoundland, where cellars kept families fed through long winters, settled on two entry designs that are worth copying. One is a double door with a small porch between, so the outer door shuts before the inner one opens. The other is a hatch inside a shed. Either way the cold room never opens straight onto January. ### Before you dig Call 811 first. The [811 program](https://811beforeyoudig.com/) says every dig needs a call a few days ahead, and warns that some utilities are buried just inches down. A cellar hole is deep and wide, which is exactly how people find gas lines with a shovel. Then look at water. Dig a test hole to the depth you plan and watch it after a hard rain. If it fills, build into a slope or above grade instead, because a cellar that floods every spring rots the crop and the timber with it. Read your county's building rules too, since a structure this size may need a permit, and a dug space with a roof can count as a building. The hole itself is the danger in this project. Soil walls look solid and then slump without warning. Slope the sides back or brace them as you go, never work alone in a deep cut, and keep the spoil pile well back from the edge so its weight does not push the wall in on you. ### Ventilation: cold in low, warm out high A sealed hole goes stale. Produce gives off heat, moisture and gases as it breathes, and the cellar needs a slow, steady change of air to carry them away. The usual layout uses two vent pipes. One brings outside air down to just above the floor, and the other leaves at the ceiling, ideally on the opposite side of the room. In cold weather the heavy outside air sinks into the low pipe and pushes the warmer, damper air up and out the high one. No fan is needed. Cold outside air drops in through the low pipe and pushes warm, damp air out through the high one. Fit both pipes with screens against mice and caps against rain, and give each a damper or plug, because opening and closing them is how you set the cellar's temperature. In fall, open them on cold nights and close them on warm days to pull the room down toward 32\. In deep winter, close them most of the way when the outside drops well below freezing, or the cellar freezes from the vent inward. In spring, the vents stay shut during the day to hold the stored cold as long as possible. ### Keeping the air damp Most root crops want air wetter than a house ever gets, and the earth helps. A floor of packed earth or gravel gives off moisture, while a poured concrete floor dries a room out. Among the ways the K-State bulletin lists to raise humidity in storage are wetting the floor and controlling ventilation against the size of the load. In a home cellar that means a watering can on the gravel when the hygrometer drops, and vents opened less in dry spells. Packing does the rest. Carrots, beets and parsnips keep best buried in damp sand, sawdust or peat in boxes or crocks, which hold a pocket of near-saturated air around each root. Trim the tops to about an inch, leave the roots unwashed, and layer them so they do not touch. Cabbage can hang by its roots from the ceiling or sit wrapped in newspaper on a shelf. The alliums go in mesh bags or braids on the top shelf, where the air is driest. Too much moisture is the other failure. Water dripping from the ceiling means warm, wet air is not getting out: open the high vent more, and keep condensation from falling on the produce. ### Storing potatoes without power Potatoes are the crop most cellars are built around, because they carry the most calories per bushel and keep for most of a year when handled right. [Utah State University Extension](https://extension.usu.edu/yardandgarden/research/potatoes-in-the-garden) lays out the steps, and the first one happens before the cellar. Dig storage potatoes after the vines have died and the skins have set, which USU says you can tell because mature skin is hard to rub off. Let the soil dry, brush it off, and do not wash them. Then cure them for two to three weeks at 55 to 60 degrees with high humidity. Curing heals the scrapes and cuts from digging, and an uncured wound is where rot starts. A dark corner of a garage or barn in early fall is often the right temperature. After curing, USU says to keep potatoes in the dark at 40 to 45 degrees through the winter, and the K-State table puts the late crop at 38 to 40 and 90 to 95 percent humidity. Three things go wrong most often: * Light. Exposure turns tubers green and builds a bitter compound under the skin. USU says a small green patch can be cut away and a very green potato thrown out. Cover the bins with burlap or a board and keep a light switch out of the cellar. * Fruit. USU warns against storing potatoes with apples or pears, because the ethylene the fruit gives off makes tubers sprout. * Still air. Good circulation cuts rotting and sprouting, so use slatted bins or crates a few inches off the floor and off the walls, never a solid heap. Freezing is the fourth risk, and the hardest to undo. The K-State bulletin lists potatoes among the crops most likely to be ruined by one freeze, so set the potato bins at the far end of the room from the intake vent and the door. Sort the crop before it goes in. Eat the cut, bruised and small ones first and store only sound tubers. Then go through the bins every week or two. A single soft potato spreads rot to its neighbors, and the smell tells you something has turned before you find it. ### Running the cellar through the year Load it in fall as the nights cool. The produce arrives warm from the garden, and the room needs cold nights with open vents to pull it down. Crops that hold in the ground, like carrots and parsnips under a thick mulch, can wait outside until the cellar is cold enough to take them. Watch the thermometer through winter, and use the maximum/minimum readings, since the low you missed at four in the morning is the one that freezes a bin. If something does freeze, the K-State bulletin advises letting it warm up slowly and not handling it while it thaws, then using it first. Keep a few jugs of water on the floor in very cold snaps. Water gives off heat as it freezes, which slows the room's slide below 32. Spring is when cellars run out of cold. As the ground warms, the room creeps up, potatoes start to sprout and apples soften. Plan to eat down the stored crop by then and move what is left into canning or the dehydrator. The cellar is empty by early summer, which is when you clean it: sweep out the old sand and debris, air it, and let it dry before the next harvest. Canned goods are happy here too. Home-canned jars and commercial cans keep their quality longest in a cool, dark place, and our [food storage shelf life chart](/food-storage/food-storage-shelf-life-chart) gives the times for each. Shelve the jars above the damp floor and clear of the vents so their lids do not rust. ### My take: start with what you already have I'd start in the basement before I'd start digging. A walled-off north corner with a vent to the outside costs a weekend and some foam board, and one winter in it teaches you how your crops and your climate behave. If you can keep a few bushels of potatoes and a box of carrots sound until March in that room, you know what you need from a dug cellar and how big to build it. If I were building into the ground, I'd choose the hillside over the flat-ground hole wherever there is a slope, for the drainage alone. I would spend more on the vents, the door and the drainage than on the walls, because those decide whether the room stays cold and dry. And I'd buy the hygrometer and the maximum/minimum thermometer before the first shovel goes in. A cellar works best as one part of a food plan. Stored roots carry the winter, the [laying flock](/homestead/backyard-chickens-for-eggs) supplies fresh protein, and the sealed staples in the pantry cover the gap in late spring when both run thin. If the power goes out in summer, a cool cellar also buys time for a fridge that has warmed up, as our guide to [how long food lasts when the freezer loses power](/food-storage/freezer-power-outage-how-long-food-lasts) explains. The rest of our guides to growing and keeping food are in the [homestead section](/homestead). ### Sources * [University of Maine Cooperative Extension (reprinted from Kansas State University): Bulletin #4135, Storage Conditions for Fruits and Vegetables](https://extension.umaine.edu/publications/4135e/) * [Utah State University Extension: How to Grow Potatoes in Your Home Garden](https://extension.usu.edu/yardandgarden/research/potatoes-in-the-garden) * [Wikipedia: Root cellar (citing Bubel and Bubel, Root Cellaring, 1991)](https://en.wikipedia.org/wiki/Root%5Fcellar) * [811 Before You Dig (Common Ground Alliance)](https://811beforeyoudig.com/) How we write: we work from extension, public health and emergency-management guidance and say what we have not tested. See our [editorial policy](/editorial-policy). ### Root cellar questions What temperature should a root cellar be? Aim for the low end of 32 to 40 degrees Fahrenheit for roots, cabbage and apples, and a little warmer, around 38 to 40, for late potatoes. Below 32 most produce freezes, so the floor of the range matters as much as the top. Can I turn part of my basement into a root cellar? Yes, if you can wall off a corner from the furnace and the heated rooms. An outside wall on the north side, an insulated partition and a window or pipe for outside air give you a cold room without digging. Why did my potatoes turn green? They saw light. Light makes potatoes build a bitter compound under the skin, so trim small green patches and throw out tubers that are green all over. Cover the bins and keep the door shut. Can apples share the cellar with potatoes? Not in the same bin, and ideally not in the same room. Apples and pears give off ethylene, which makes potatoes sprout and can spoil cabbage and carrots near them. Store fruit on its own, high and near the exhaust vent if it has to share. How long will a root cellar keep food? It depends on the crop and on how steady you hold the room. Under the conditions the K-State storage table lists, mature carrots keep seven to nine months and late potatoes five to ten. A cellar that swings with the weather keeps them for far less, so a thermometer and a hygrometer earn their place on the wall. Written by Ruth Calloway Pantry, water and homestead skills Ruth Calloway writes Larder & Well's guides to food storage, water, off-grid power and the old household skills. She works from extension-service bulletins, USDA and Ready.gov guidance, manufacturer manuals and years of homesteader discussion threads, and she says plainly where the sources disagree. She does not claim to have tested what she describes; when a method is untested or risky, her articles say so. [rcalloway@larderandwell.cc](mailto:rcalloway@larderandwell.cc) Last checked 2026-11-10 --- [Larder & Well](/) Keep the household fed, watered and warm when the stores close. Food storage, water, off-grid power, homestead skills and the old ways, written for American households that want to stay fed, watered and warm when the grid, the economy or the supply chain fails. [Send a correction or a question](/contact) © 2026 Larder & Well. Independent, written from sources you can open. A page that ever carries a paid link says so above it. Nobody pays for a place in our guides.