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Small Farmer's Journal
PO Box 1627
Sisters, Oregon 97759
800-876-2893
541-549-2064
agrarian@smallfarmersjournal.com
Mon - Thu, 8am - 4pm PDT

The Woodfired Bottom-heated Greenhouse Bench

The Woodfired Bottom-heated Greenhouse Bench

Cultivating Questions Concerning the Bio-Extensive Market Garden

The Woodfired Bottom-heated Greenhouse Bench

by Anne and Eric Nordell of Trout Run, PA
illustrations by Ed Ochsner of Hohenwald, TN

Hi Anne and Eric,

This is Sam and Rich Wickham writing to you. We have been living and working on farms in the Finger Lakes for the past few seasons and, by way of our Amish neighbors and all the talented draft powered farmers in the area, we have been inspired to pursue farming with horses.

We have been passively gleaning knowledge from you through the SFJ, the world wide web, and your wonderful DVD and booklet which we got for Christmas this year. Your in depth, thoughtful coverage has been, far and away, the most valuable resource to us in our fledgling farming career. At first, we were just excited to find another couple who wanted to keep their farm a two person operation and how they went about that. However, it quickly became apparent that that knowledge was the very least we would stand to get out of poring over your old SFJ articles.

Anyway, we think we have exhausted our google search capacity in trying to find out more about your farm so we figured we had better sit down and write a letter to you both. We are quite curious about your wood stove greenhouse seedling set up. It has been difficult for us to determine the possible dimensions and arrangement of the system. Any insight into this would be much appreciated. Also, are you only heating up the stove at night or is it continuous throughout the day?

We are not prone to pestering but we are so intrigued by this idea that we just can’t help ourselves in this instance. We have been wanting to drop a line your way anyway to let you know that your work has elevated our understanding of farming (and appreciation of the craft) by leaps and bounds. Thank you for your generosity!

Take Care,
Sam and Rich
Caseville, MI

Before launching into the construction details of the bottom heated bench, we should explain why we chose this unusual method of heating the greenhouse in the first place. Looking for a low tech, low cost heat system which did not require electricity, we were intrigued with the nineteenth century greenhouse design in Peter Henderson’s Gardening for Profit. [see below – ed.] The flue from the wood stove of this renowned market gardener’s greenhouse ran underneath the length of the central bench and back again before joining the chimney built directly on top of the firebox. The heat from the stove created enough draft in the stack to pull smoke and heat through the long horizontal flue, warming the 20′ by 60′ greenhouse and providing bottom heat to most of the plants.

As much as this innovative heating system appealed to our minimalist outlook, we were concerned that this setup would be overkill for the 10′ by 16′ structure we intended to build in time for the 1988 greenhouse season. It seemed to us that a clean burning fire would make the small greenhouse too hot for the health of the plants and that moderating the greenhouse temperature with a smoldering fire would quickly lead to creosote buildup in the horizontal flue, a sure recipe for a chimney fire. We decided a safer, less polluting alternative would require thermal mass directly under the plants to capture the intense heat from a clean burning fire and release the warmth slowly for twelve or more hours.

The Woodfired Bottom-heated Greenhouse Bench

It took several incarnations to come up with a satisfactory design for the bottom heated greenhouse bench. In the final version we used two 55 gallon drums welded end-to-end for the firebox and a salvaged piece of 12” stainless steel chimney for the horizontal flue. (Metal culvert pipe or gasline casing might work just as well.) We learned the hard way that a large firebox and flue are necessary to dissipate the intense heat into the surrounding air chamber and to minimize heat stress on these components.

To shield the wooden greenhouse structure from the heat, we built the end walls of the bench with 4′ by 4′ pieces of sheet metal, cutting a large enough hole in one end for the door of the barrel stove and a smaller hole at the other end for the horizontal flue to exit and join the chimney outside of the greenhouse. A farmer that copied our design but neglected this safety feature had to call the fire department when the heat from the stove caught the greenhouse on fire.

The Woodfired Bottom-heated Greenhouse Bench

For the same reason, we built the side walls of the bench with concrete blocks. We placed salvaged grating from a sidewalk heat vent across the top of the block walls to support an 8″ layer of field stone and gravel, doubling the depth of this thermal mass over the barrel stove where the most heat is radiated. The weight of the stone on the grate keeps the side walls in place so mortar is not needed when laying the block.

The stove and flue rest on a bed of gravel sloped so that the pipe rises 12″ over the 16′ length of the bench. This modest slope along with the warmth retained by the thermal mass surrounding the flue produces a strong and dependable draft. When heat waves replace the smoke coming out of the chimney, we close the damper installed in the horizontal flue just outside of the greenhouse to hold as much heat inside the bench as possible. Managed this way, there is no creosote or ash buildup in the flue or chimney.

Since our goal is a brief, clean burning fire, we load the barrel stove with a couple of armloads of very dry wood. Scrap wood, tree trimmings, small pieces of seasoned hard wood all work well. For a number of years we used hemlock slabwood from a local sawmill. A half cord of slabwood was more than sufficient for the typical greenhouse heating season running from mid-March to mid-May.

The Woodfired Bottom-heated Greenhouse Bench

Normally, one firing around six in the evening is all that is needed to heat the bench overnight. (We fire up the stove a couple of times at the start of the greenhouse season to warm up the thermal mass.) If the thermometer dips into the twenties or lower, then we load the stove twice a day, morning and evening. We have never had to get up in the middle of the night to heat the greenhouse. Firing the stove a couple of times in a row, on the other hand, can get the stones so hot that they will fry the plants resting on top. Keep in mind that heat released from the bench keeps the greenhouse just 20-30 degrees above the outside temperature. That is fine with us because the combination of warm potting soil and cool air produces plants with the stocky topgrowth and large root system necessary for trans- planting without irrigation. Dryland planting also benefits from larger plugs than normal. For example, we use 72 cell flats for lettuce and 50’s for the brassicas.

Only one of the two greenhouse benches is heated. This arrangement is adequate for space heating because we insulated all four sides of the small structure with foam board sticking at least 18″ in to the ground. By contrast, a grower who tried a single wood heated bench in the middle of a larger, uninsulated hoop structure found the results unsatisfactory.

The only reason this small heated structure meets our needs is our business is based on successive plantings of cool season vegetables and we move the flats through three growing areas: our wood heated house with enclosed front porch for germination (beginning mid-February); the bottom heated greenhouse for early growth of the vegetables; and an adjacent unheated 12′ by 28′ hoophouse for the later stages of growth and hardening off.

The Woodfired Bottom-heated Greenhouse Bench

So far, this low cost, multi-stage system has reliably produced enough plants for our small market garden. Over the course of the 2014 growing season we transplanted 15-1/2 of our 380′ rows to lettuce set 9″ apart (grossing $10,436), 7 rows of onions @ 7-8″ ($2,748), 5-1/4 rows of broccoli spaced 20″ ($2,704), 3 rows of kale ($2,532), 3 rows of leeks ($1,200), 1 row of peppers ($685), 1 row of cabbage ($519), 4-1/4 rows of miscellaneous vegetables ($2,789), 4,360 sq. ft. of transplanted hoophouse crops ($11,188) and bedding plants for sale ($2,713). A much larger heated greenhouse would be necessary if we grew lots of warm season crops, like tomatoes, melons and peppers.

Also in 2014, our first summer intern replaced the rusted out grates in the bottom heated bench. The refurbished greenhouse attracted a lot of attention at the Columbus Day tour, probably because it was the only spot on the farm that looked somewhat warm on that raw, chilly day.

In closing we should point out that our make-do growing system requires moving every flat between three different buildings and an intimate understanding of which part of the heated bench is best suited for each crop. There is a reason why most growers eventually put up a single structure for all the stages of plug growth. Although the initial investment and annual fuel costs are significantly higher than the woodfired bottom heated greenhouse, one large hoop structure with automated heating is much more labor efficient and straightforward to manage.


Heating By Flues

from Gardening for Profit by Peter Henderson (1890)

When personal attention can be given to the fires, by heating greenhouses with flues a great saving in cost can be made; in fact, nearly half the cost of construction; for we find that the hot-water heating apparatus is usually half the cost of building greenhouses, while, if heated by flues, the cost would be no more than ten percent of the whole. A new method of constructing flues (or rather a revived method, for it originated in 1822,) has been in use for the past few years, which has such manifest advantages that many now use it who would no doubt otherwise have used hot water heating. Its peculiarity consists in running the flue back to the furnace from which it starts and into the chimney, which is built on top of the furnace. As soon as the fire is lighted in the furnace, the brick-work forming the arch gets heated, and at once starts an upward draft, driving the cold air from the chimney, which puts the smoke flue into immediate action and maintains it; hence there is never any trouble about draft, as in ordinary flues having the chimney at the most distant point from the furnace. It will be understood that the chimney into which the flue is returned is placed on top of the arch of the furnace, and not in it, as some might suppose.

By this plan we not only get rid of the violent heat given out by the furnace, but at the same time it insures a complete draft, so that the heated air from the furnace is so rapidly carried through the entire length of the flue, that it is nearly as hot when it enters the chimney as when it left the furnace. This perfect draft also does away with all danger of the escape of gas from the flues into the greenhouse, which often happens when the draft is not active. Although no system of heating by smoke flues is so satisfactory as by hot water or steam, yet there are many who do want to go to the expense of hot-water heating, and to such this revived method is one that will, to a great extent, simplify and cheapen the erection of greenhouses.

The Woodfired Bottom-heated Greenhouse Bench

The flue will always “draw” better if slightly on the ascent throughout its entire length. It should be elevated in all cases from the ground, on flags or bricks, so that its heat may be given out on all sides. The inside measure of the brick flue should not be less than eight by fourteen inches.

After the flue has been built of brick to twenty-five or thirty feet from the furnace, cement or vitrified drain pipe, eight or nine inches in diameter, should be used, as they are not only cheaper, but radiate the heat quicker than the bricks; they are also much easier constructed and cleaned. Care should be taken that no wood work is in contact with the flue at any place. It should be taken as a safe rule, that wood work should in no case be nearer the flue or furnace than eight inches. In constructing, do not be influenced by what the mechanics will tell you as few of them have any experience in such matter, and are not able to judge of the dangers resulting from wood work being in close contact with the heated bricks. There are scores of greenhouses burned every year owing to carelessness or ignorance in allowing the brick work to be too close to the wood. The cost of such a greenhouse, at present prices, heated by flue, would be about six hundred dollars, or about sixty cents per square foot covered by the greenhouse.

Spotlight On: People

Typical Range Ride

Typical Range Ride

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I head up the steep trail through the rocks and sagebrush behind our house. The smell of dewy sage fills my nostrils as my horse brushes the shrubs along the trail, and a horned lark flits up from her nest on the ground as we go by. A mother grouse bursts into the air and does her broken-wing act (her strategy to lead a predator away from her babies, who are scattering out through the grass).

Rainshadow Organics

Rainshadow Organics

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Saralee Lawrence and Ashanti Samuels are Rainshadow Organics, a burgeoning, certified organic operation which fully embraces the tenets of mixed crop and livestock farming. At its core is a full-force market garden. The entire farm comprises one hundred and eighty acres situated in the magnificent, high desert region of central Oregon and subject to a painfully short growing season (some years just slightly over 2 months).

In Memoriam Gene Logsdon

In Memoriam: Gene Logsdon

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Gene didn’t see life (or much of anything else) through conventional eyes. I remember his comment about a course he took in psychology when he was trying to argue that animals did in fact have personalities (as any farmer or rancher will tell you is absolutely true), and the teacher basically told him to sit down and shut up because he didn’t know what he was taking about. Gene said: “I was so angry I left the course and then left the whole stupid school.”

Jacko

Jacko

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By the time he was 3 years old, Jacko had grown into a big size jack, 13 hands tall and 900 pounds, and was still growing. That summer he ran the singlerow corn planter and raked the hay, proved himself handier with a single row cultivator than a single ox, getting closer to the plants without stepping on them. Gradually he had paced himself to his three educated gaits to fill whatever job Lafe required of him: fast walk for the planter and rake, slow walk for the cultivator and plant-setter, and brisk trot for the buggy.

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“Thank you for taking the time to visit our farm.” This is one of the responses that I give to the many visitors as they prepare to leave Carriage Hill Farm, an historical farm which is part of a much larger system of 24 parks within the Five Rivers Metroparks system. The main emphasis of our farm is education and interpretation of an 1880’s family farm with all the equipment and animals from the 1880’s time period.

Elsa

Elsa

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I headed out with a gut feeling not that something was wrong, but that in these conditions there soon enough would be if I did not try. I made my way more or less by instinct across the open field and through the frozen swamp. In amongst saplings, rocks, and old rusty metal and wire there is a large, red haired calf half steaming where mom is aggressively licking her and the other half is iced over where her hooves and legs appear frozen to the ground.

Building a Community, Building a Barn

Building a Community, Building a Barn

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One of the most striking aspects of this development is the strength and confidence that comes from this communal way of living. While it is impressive to build a barn in a day it seems even more impressive to imagine building four barns or six, and all the rest of the needs of a community. For these young Amish families the vision of a shared agricultural community is strong, and clear.

Field Weeds and Street Boys

Field Weeds and Street Boys

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So, our farming system to feed hungry street boys is to have them farm “weeds”. As we have all experienced, weeds are perfectly adapted to their climate, are robust and need no fertilizer nor any of the insecticides to enhance a good crop. Because we are aiming for long term diversified permaculture (this is a Shea native tree area), we needed some very quick marketable crops while we wait for the trees to mature. These field weeds intentionally farmed have a ready market in the big city 5 km north.

Farmrun - Sylvester Manor

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Sylvester Manor is an educational farm on Shelter Island, whose mission is to cultivate, preserve, and share these lands, buildings, and stories — inviting new thought about the importance of food, culture and place in our daily lives.

Birth of a Farm

Birth of a Farm

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“Isn’t it nice?” I offer to my supper companions, “to see our beautiful horses right while we’re eating? I feel like I’m on a Kentucky horse farm, with rolling bluegrass vistas.” I sweep my arm dramatically towards the view, the rigged up electric fence, the lawn straggling down to the pond, the three horses, one of whom is relieving herself at the moment. “Oh, huh,” he answers. “I was thinking it was more like a cheesy bed and breakfast.”

NYFC Bootstrap Videos The Golden Yoke

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Cindys Curds & Whey

Cindy’s Curds & Whey

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The Burgess dairy farm and cheese factory are sustainable operations, meaning that nearly every by-product is re-used or recycled. For example, the usually-discarded whey goes to feed their own pigs, producing an exceptionally tasty, lean pork. Whey is the liquid portion of milk that develops after the milk protein has coagulated, and contains water, milk sugar, albuminous proteins, and minerals.

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You’d never be able to harvest the broccoli or the hay or milk the cows or make the cheese if it were subject to government process. Not only are our industrial farms too big…

Cuban Agriculture

Cuban Agriculture

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In December of 1979, Mary Jo and I spent two weeks traveling in Cuba on a “Farmer’s Tour of Cuba”. The tour was a first of its kind. It was organized in the U.S. by farmers, was made up of U.S. farmers and agriculturally oriented folks, and was sponsored in Cuba by A.N.A.P., the National Association of Independent Farmers. As we learned about farming we also learned how the individuals, farms, and communities we visited fit into the greater social and economic structure of Cuba.

LittleField Notes A Trip to the Auld Country

LittleField Notes: A Trip to the Auld Country

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I’ve come to the north of Scotland this October almost by accident. And I find myself standing on the windy, rocky point of land that is northernmost on the isle of Great Britain. The sea lies before me: the flooding tide from the Atlantic pours in on my left where it collides with the North Sea pouring in from the right, the opposing currents whipping up a frenzy of white capped, tidal confusion: for sailors past and present, treacherous waters indeed. Straight ahead, across the seething waters of Pentland Firth lie the Orkney Islands, my ultimate destination.

Harnessing the Future

Harnessing the Future

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En route to a remote pasture where the Belgian draft horses, Prince and Tom, are grazing, we survey the vast green landscape, a fine mist hovering in distant low lying areas. We are enveloped in a profusion of sweet, earthy balance. Interns and other workers start their chores; one pauses to check his smart phone. Scattered about are many animal-powered rustic implements. This rich and agriculturally diverse, peaceful place is steeped in contrasts: modern and ancient.

Great Oregon Steam Up

Great Oregon Steam-Up

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I went to the Great Oregon Steam-Up over in Brooks, Oregon, near Salem. Lynn has been invited and has wanted to attend for years, but this time of year might very well be the busiest time of year for him. He’s always farming or writing or editing or painting or forecasting or businessing or just generally fightin’ the power, yo. It’s nuts, I don’t know how he does it all. So, when I told him I was going to go, he was very interested and wanted a good report.

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Small Farmer's Journal

Small Farmer's Journal
PO Box 1627
Sisters, Oregon 97759
800-876-2893
541-549-2064
agrarian@smallfarmersjournal.com
Mon - Thu, 8am - 4pm PDT