Air Flow Patterns
Figure 1
Happiness belongs to the self-sufficient.
Aristotle
The kind of root cellar you build or adapt from what you’ve already got, will depend on the floor plan of your house, the lay of your land, and the prevailing winter temperatures and snow cover in your area. If you have an old house with an unheated, dirt-floored basement room you’re all set. With slight modification, or in some cases none at all, you may have a near-ideal vegetable storage cellar. In a house with a heated basement, it may be possible to partition off an unheated corner for vegetable storage. If you prefer an outdoor root cellar, you can either dig into a hill or go straight underground and top the cellar entrance with a bulkhead door, patio, or porch. If you live in an area where winter temperatures are often below zero degrees F and snow cover is heavy, you may prefer climbing a ladder down a hatch into an under-porch storage pit to shoveling through drifts to get to a hill-cave root cellar.
If your winters are mild, with average temperatures much over 30 degrees F, you will not be able to achieve the most desirable low temperature in your cellar for the keeping of root vegetables. To compensate, though, these vegetables will probably keep very well in the garden row for you and the warm keepers like squash, onions, and sweets should do very well in a cool corner of your house.
Whether you’re modifying an existing space or building from scratch, you’ll want to consider the ground rules for a good root cellar when drawing up your plans. While it is not always possible to arrange a textbook-perfect root cellar on the homeplace with just the right moisture and temperature for each vegetable, it makes sense to understand the basic principles of root cellar construction. Then you can at least aim in the right direction. If you can’t provide ideal conditions, don’t despair. Plenty of people live quite well all winter from root cellars that don’t precisely meet all of these basic requirements. On the other hand, if you are building a storage area from the ground up, you might as well do it right.
We’re thinking, for example, of a house built for the pastor of a nearby church by his parishioners. The well-meaning builders put in a root cellar under the house, but they did not provide any means of ventilation, and the pastor, who was also an enthusiastic gardener, found that his vegetables didn’t keep as long as they should. It’s still possible to ventilate that cellar, but it would have been much easier to provide ventilation during initial construction.
You’ll find plans and drawings for different kinds of root cellars in chapters 15 and 16 of this section. Before you start nailing or digging, though, here are some important factors to consider:
There are three basic conditions your root cellar should provide. The closer you can come to approximating these ideal conditions in your vegetable storage area, the better your vegetables will keep.
Temperature should be your first consideration. The largest group of storage vegetables and fruits (see chart, Storage Requirements of Vegetables and Fruits) keep best in a cold place. The warmer temperatures required by squash, sweet potatoes, pumpkins, onions, and so on are easier to provide in the average home without making any special arrangements. So, although not all good keepers need cold, we’ll concentrate here on low-temperature storage because that takes the most doing to arrange.
A thermometer is a necessary tool for a well-run root cellar. One with minimum-maximum readings will give you a good picture of the kind of temperature variations you’re working with.
A good root cellar can both borrow cold and keep cold. You borrow cold by digging into the ground, where the temperature well below the frost level remains a fairly constant 52 degrees F or so. This works two ways. The deep-down earth temperature is slow to be affected by ultra-cold surface temperatures too, so your underground vegetables have an extra margin of protection against freezing. You also borrow cold by providing some means of admitting cold night air to the cellar, especially during the fall when days may be too warm to promote good keeping. Three effective cold air ducts are:
If you can maintain temperatures between 32 and 40 degrees F, you have an excellent storage place. A temperature range of 40 to 50 degrees will still permit shorter-term storage of root vegetables and apples and will keep onions and some of the short-lived storage vegetables like peppers, tomatoes, and eggplant in good shape for a month or so. In an indoor root cellar, the area close to the ceiling will be a few degrees warmer than space near the floor, so you’ll have at least a small difference in conditions which you can use to advantage in placing vegetables with slightly different storage requirements.
Once you’ve cooled the food cellar, you want to keep it cold. Here again, you need some way of letting cold air in so that you can adjust the temperature if it begins to rise. Even more basic, the placement of your cellar will help you to keep it cold. The best spot for a basement root cellar is on the northeast side where the sun’s warming influence is the weakest. Next best would be the northwest wide, especially if trees or bushes shade the area from the western sun.
Most outdoor root cellars are dug into a north-facing hill or are underground on the north (coolest) side of the house. (You’ll find exceptions to this rule in some of the northern states and Canada, where temperatures plummet well below zero in winter, and stay there. Some of the old-time outdoor root cellars in these areas are built on southern exposures so that winter access will be somewhat easier. Once winter sets in, it’s plenty cold there even though these cellars get more sunlight than it would seem they should.)
In a basement vegetable closet, it’s important too, of course, to keep out heat. Build the closet in a corner away from the furnace, heating ducts, and hot water pipes. If you can’t escape the warming pipes, insulate them with a wrapping of fiberglass or one of the pop-on foam tubes.
Many underground root cellars are built with double doors that form an airlock or anteroom which helps to keep warm summer air out of the cellar and also to prevent undue chilling of the produce in severe winter weather.
Insulation also helps to maintain a stable temperature in the storage space. It won’t help much, in a room you’ve simply partitioned off from a heated basement, to open a window to cool the room. Heat from the basement will warm up the space, and the warmth from the heated living area above will also influence temperatures in the cool room below. The solution is to insulate not only the warm inner walls, but also the ceiling and door, of a partitioned vegetable closet. Insulation should not, of course, be applied to the cold outside walls. Old-timers used sawdust, wood shavings left from planning, cork dust, and even cinders, straw, or dry leaves. More recently developed materials with higher resistance values include fiberglass, urethane, Styrofoam, mineral wool, and vermiculite or perlite.
Although brick and concrete walls look substantial, their insulating value is quite low. If your cellar temperature runs around 60 degrees F, you’ll need the following thicknesses of material to keep the root cellar cold:
Urethane and Styrofoam are flammable. Cellulose fiber, which is used as loose fill, should have been treated with fireproofing materials; check the bag label. Sawdust and mineral wool used as wall insulation will settle over a period of time. Planer shavings are less likely to settle if they are tamped into place rather firmly. Shavings should be compressed to a density of about seven pounds to the cubic foot. Some kinds of insulation, fiberglass batts for example, have a vapor barrier attached to one surface. Be sure to apply the insulation with the vapor barrier on the outer, or warmer, side so that moisture doesn’t condense on the insulation and spoil its effect. When using loose, dry insulation you can apply a sheet of polyethylene between the insulation and the warmer wall surface to keep out moisture that would otherwise condense at the interface of warm and cool surfaces. When insulation becomes wet it loses its effectiveness because it then has less trapped air and it often packs down and thus loses volume.
High humidity is the second requirement for effective root cellar storage. As you’ll note in the chart Storage Requirements of Vegetables and Fruits, most root crops and leafy vegetables keep best at a humidity of 90 to 95 percent. Providing plenty of moisture helps to prevent these foods from shrivelling.
How can you measure the humidity in your root cellar? It’s not as difficult as you might suppose. Simply purchase a hygrometer at a hardware store. The hygrometer measures humidity. Most of the successful grower-keepers we’ve met use a thermometer but do not actually measure humidity. The modest expense would be well worth your while, though, if fine-tuning your storage conditions would increase the amount of food you can put by for winter.
There are three ways to achieve the necessary humidity in a root cellar. For one thing, a cellar with a dirt floor will contain more natural moisture than one with a concrete or stone surface. In many older homes, one basement room was purposely left unfinished for just this purpose, even when “improvements” like furnaces were added to other parts of the basement.
We had such a room in a turn-of-the-century house we once owned. The furnace room had a concrete floor but one-third of the large basement are retained the original dirt floor. Potatoes, carrots, and apples kept very well for us there. We simply mounded up the potatoes on the floor and covered them with loose fine dirt. The room was, in fact, so damp that squash kept there spoiled early. In our new root cellar, we’ve left bare earth in a corner of the small basement area and have spread gravel on the packed earth. This helps to keep feet dry if the ground really gets damp. In addition, should the storage area need more moisture, we can easily sprinkle the gravel with water and its large surface area will evaporate the moisture readily into the air.
And that’s the second way to keep humidity high — add some water, either by sprinkling the floor, spreading damp (but not dripping wet) burlap bags over the produce, or setting pans of water on the floor. Such measures are often necessary in the fall when you’re first stowing the produce away. Basement root cellars are much more likely than dug-in root cellars to need added humidity.
In a very moist area you can often simply keep the root vegetables uncovered in bins and they’ll stay smooth and firm. If your humidity reading falls short of the ideal, though, you’ll often have better results if you use a third technique — packing the root vegetables, especially carrots, beets, and parsnips, in damp sawdust, sand, or moss to cut down surface evaporation. You can also encase vegetables in plastic bags to prevent moisture loss, but this can be tricky. The bags should be perforated to permit ventilation, or surface molds that thrive on stagnant air will take over and spoil the vegetables.
It’s important to remember that cool air can absorb less moisture than warm air. For this reason, you get a pretty unstable situation in a place that’s both cold and very damp. A slight drop in temperature can mean that air that, at 34 degrees F, let’s say, had room for a bit more moisture, suddenly becomes fully saturated at 32 degrees. When this happens, you’ve reached the dew point, and the excess water that the air can no longer hold begins to condense on wall, ceiling, and even vegetable surfaces. When produce becomes wet it’s more likely to spoil, even at low temperatures. So you see that your aim is to achieve a balance.
Since it is impossible to control all these factors entirely, you will often have some condensation, especially in dug-in underground root cellars. Therefore it is a good idea to keep the ceiling surface smooth, with no beams or other structural parts projecting into the room. When a beam protrudes, it traps warm damp air in the poorly ventilated places where it joins the walls and ceilings, and this causes undue condensation. This is why some old, carefully built root cellars have arched ceilings, with no corners to trap warm air. If condensation is a problem in your cellar, you might want to spread dry burlap sacks or layers of newspapers over the food to absorb any water that might drip off the ceiling.
Ventilation, the third key to successful root cellar operation, affects both temperature and humidity. Admitting cool night air to the cellar, as we have seen, helps to chill the area to the desired low temperature more quickly in the fall. Equally important, adjusting air intake can help to reduce excessive humidity and thus prevent undesirable condensation. In addition, the air circulation set in motion by a good ventilating system effectively removes both vegetable odors and ethylene gas given off by stored fruits, which might otherwise produce off-flavors in other foods and sprouting in potatoes in stagnant air.
To understand how air can circulate through a root cellar, remember that warm air rises and cool air falls. In a large or tightly enclosed cellar, you’ll need both an air intake and an air outlet. The intake opening should be low, and the outlet should be placed high and ideally on the opposite side of the room to promote more complete circulation of air. Cool air will enter through the low intake and warm air will be released through the outlet. In a small storage area or one with many cracks where air can enter, such as an old stone foundation, a single outlet, placed high to exhaust warm air, may be sufficient.
Figure 1
Figure 2
Figure 3
The diagrams show the air flow pattern in three different root cellars. Figure #1 with the air intake and air outlet vents on opposite sides of the room and a space between the shelves and the wall, is an ideal setup. In figure #2, the cellar is the same except that there is no gap between the shelves and the wall for air circulation. Figure #3 shows a large cellar with intake and outlet vents on the same wall. Such an arrangement would be adequate for a small space — five by five or so — but in a longer room the incoming cold air is blocked by a curtain of rising warm air, so it tends to stay near the entrance. (As the cold air moves into the room, it warms up and then rises.)
If you’re building a new concrete block or stone root cellar, we’d advise you to include both air intake and exhaust pipes in your plans. Use any reliable plastic or metal drainage pipe, clay tile or scrap pipe, or commercial ventilating blocks, and screen the exterior openings to keep rodents out. For root cellars six by eight feet or smaller, use a vent pipe with a four-inch diameter. Cellars larger than six by eight will often function better with a six-inch pipe.
When installing the exhaust pipe, keep its open edge flush with the cellar wall. It should not protrude inside the cellar, because the dead air pocket thus formed would encourage condensation. In some European root cellars both the intake and exhaust pipes are insulated to prevent condensation.
In a well-planned basement storage room designed by the Canadian Department of Agriculture, cross ventilation is achieved in the area by running a fresh-air duct from the outdoor window along the wall for several feet, ending with a damper that can be flapped shut to exclude cold air when necessary. Warm air exhaust in this Canadian system is handled by a small fan placed in the other half of the window not occupied by the intake duct. To operate this system automatically, the Canadian specialists suggest using a differential thermostat with one bulb kept inside the storage space and the other placed outdoors where the sun will not shine on it. When the inside temperature rises above a preset level, then, the exhaust fan will automatically start to vent warm air and cold air will rush in through the open intake duct to replace the outgoing air. The fan shuts off when the room temperature is reduced to the point you’ve chosen.
If extra-cold temperatures threaten your stored food, you might wish to use the simpler plan of installing a thermostat in the root cellar with a bell, light, or other indicator, outside the cellar, set to go off if temperatures drop dangerously low.
Here again, these are refinements that might be considered if your area experiences severe freezes or if your stored food supply is precarious or vital enough to make them worthwhile. None of the root cellaring folks we interviewed had found it necessary to use any of these mechanical aids.
After providing for the three factors vital to a workable storage area — temperature, humidity, and ventilation, you’ll want to make note of some other considerations as you plan for your vegetable independence system.
The more convenient your root cellar is, the more useful it will be to you. As we mentioned above, though, your average winter snowfall and amount of drifting will influence the placement of your cellar. In parts of Canada where snow is deep, it’s the custom to build root cellars under the living quarters or an attached porch, often with access by a trapdoor and ladder. People would rather negotiate the ladder with an apron full of apples than slog through three feet of snow in a biting wind to an outdoor root cellar. Other things being equal, though, a root cellar that is close to the house, easy to clean, well lit (a bare light bulb is fine), and not too unhandy to climb into will give you the most pleasure and satisfaction. When possible, have the door open outward in case the floor is jammed with bins and crates. A well-built root cellar lasts a long, long time so extra care in planning for convenient use is worthwhile.
It’s true that an electric light (or an available kerosene lantern) is a big help when you go to plunder your store, but between times the root cellar should be dark. Light deteriorates some storage vegetables and encourages sprouting in potatoes. Sun shining into the room can also raise the temperature higher than it should be. If you ventilate a basement room by raising an outside window, be sure to shade the window.
You want your root cellar to be damp, it is true, but you don’t want it to be waterlogged. The food should never be in direct contact with water. It’s a good idea, especially in clay soil, to lay a three-inch bed of 2B-size gravel around the perimeter of an underground cellar and put perforated drainage pipe on the gravel to carry off excess water. We’ve seen some good old basement root cellars in which humidity was kept high by running water, but that water was an underground spring that was channeled. It entered through a pipe, coursed through a concrete trough along one wall and ran out the low end of the cellar through another pipe. Few partitioned cellars have a problem with drainage; usually, especially if the floor is concrete, they’ll need added humidity.
Use nontoxic materials in this food storage area. We wouldn’t recommend creosoted wood, for example, for bins or shelves that might touch the vegetables. When ventilation is poor and humidity high, shelves made of pine or spruce may rot within several years, especially if they are not slatted to allow for drainage of condensed moisture. If you have your own woods, you might find it worthwhile to cut cedar, oak, or locust for lumber as we have done. Locust logs should be seasoned for a year before being milled into boards. We learned, when we took fresh locust logs to the sawyer, that it is nearly impossible to saw boards of even thickness from freshly cut locust. The slightly wedge-shaped boards we got from our green locust logs were fine for rough construction, but the logs would have yielded more boards, and straighter ones, if they had been aged.
Oak is so strong and durable that you can use one-inch oak planks for shelving. Next best would be Douglas fir, but you’ll need to use two-inch boards for shelves made of fir. Pine and spruce, less durable woods, should also be two inches thick for shelves. With good ventilation, untreated pine boards should last for five to eight years. Make all bins and walkways slatted, to encourage air circulation. If you can make shelves movable and bins small enough to lift easily, the necessary annual cleaning of the root cellar will be easier.
Half-bushel baskets are light in weight and easy to handle. Crates utilize space more efficiently and they may be stacked. Here is a plan for a sturdy storage tray that stacks well and permits good ventilation. Convenient dimensions would be about 16 by 22 inches and 3 to 12 inches deep (3 inches for grapes, 6 to 12 inches for apples or potatoes). Corner posts should be 2 to 3 inches higher than the body of the crate.
Nail two slats on each side to corner support posts. Then nail 3/8-inch boards across the bottom. The posts hold the crates apart when they’re stacked. For extra heavy use add reinforcements at the corners.
The use of salvaged materials can often reduce construction costs considerably. Keep track of what goes into your root cellar and how much you spend. Within five years you may well consider this one of your better investments.
How large an area do you need? Not as large as you might think. You can fit a lot of produce in a small area. A room measuring five by eight feet, for example, can hold 30 bushels of produce. If you intend to keep tubs of green vegetables with their roots still on in soil or sand, you’ll need somewhat more room. Most of the formal plans for root cellars published by state agriculture departments recommend enclosing a space ten feet square. In our consultations with root cellaring gardeners, we noted that not all of the cellars we visited were filled to capacity with vegetables and fruits. If you have the room, though, and want to make good use of the backhoe you’ve hired to dig out the space, you might want to make your root cellar a bit on the large side rather than too small, with an eye toward future expansion of your gardening activities. A space eight by eight feet should be plenty for the average family, and ten by ten feet should take care of all you can manage to produce.
Several of the gardeners we visited shared their root cellars with other members of their family. If you live in a community of gardeners or homesteaders and have an especially good site for a root cellar, you might want to consider setting up a cooperative root cellar in which storage facilities and maintenance tasks would be shared by several families. Building the cellar could be a cooperative venture too. Or an individual owner could charge a small rent or accept produce or other bartered goods for a season’s storage space in a large-capacity privately owned root cellar. As with any cooperative enterprise, it’s a good idea to spell out all terms clearly before starting.
My Aunt Margie, whose gift for vivid description is legendary in our family, tells a marvelous tale about the day her shelves full of canning jars — dozens of them, all full, of course — collapsed noisily and messily all over her cellar floor. Sad indeed. That’s only one of the things that can happen if heavy jars are kept on wood of uncertain strength in a damp place.
More common, as we’ve discovered in the damp dirt-floored basement where we kept both root vegetables and canned goods before building our new house, is that the jar lids rust through in several years. Any canned goods you intend to keep longer than a year in a damp place should be checked before using, because as the rust invades the metal lid, it eventually loosens the seal, allowing air to enter the jar. In our case it took about three years for the lids to rust enough to loosen them. If your cellar is humid enough for root vegetable storage, it is too wet for canned goods. They need a dry, cool spot. We’ve solved that problem in our new root cellar by partitioning the damp earth-floored root cellar off from the slightly warmer and considerably drier surrounding basement. If you’re starting at the beginning, then, plan a separate place for your canned goods. If it’s dry enough there, you can store your onions or squash there too, depending on the temperature range.
