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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

In Memoriam Gene Logsdon

In Memoriam: Gene Logsdon

by:
from issue:

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.”

Rope Tricks

a short piece on rope tricks from the 20th anniversary Small Farmer’s Journal.

Harnessing the Future

Harnessing the Future

by:
from issue:

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.

It Is Who We Are

It Is Who We Are

by:
from issue:

It is NOT a small world, it is a BIG world, as wide and various as you can possibly imagine. We are not alone. When we feel ourselves shut down, crowded by worry and a sense of failure, it would serve us well to remember Bulldog’s admonition, “Boss, never give up, no matter what, never give up.” Anyway, how could we? Who would put up the hay? Who would unharness the team? Who would milk the cows? Who would wax the cheese? Who would feed those woolly pigs? It’s got to be us, after all it is who we are.

Bud & Mary Rickett

Buck & Mary Rickett: Successful Small Farmers

by:
from issue:

Ten years ago I answered a classified ad and went to a small western Oregon farm to look at some young laying hens that were for sale. That visit to Buck and Mary Rickett’s place made a quiet impression on me that has lasted to this day. On that first visit in ’71 my eager new farmer’s eye and ear absorbed as much as possible of what seemed like an unusual successful, small operation. I asked what must have seemed like an endless stream of questions on that early visit.

Carriage Hill Farm

Carriage Hill Farm: Crown Jewel of Parks

by:
from issue:

“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.

Biodynamic Meeting at Ruby and Amber’s Organic Farm

Biodynamic Meeting at Ruby and Amber’s Organic Farm

by:
from issue:

One weekend I attended a Biodynamic meeting at Ruby and Amber’s Organic Farm in Dorena, Oregon, in the Row River Valley, just east of Cottage Grove. I always enjoy seeing other food growing operations, as this is such an infinitely broad subject, there is always much to learn from others’ experiences. At this farm, draft horses are used for much of the work.

Honoring Our Teachers

Honoring Our Teachers

by:
from issue:

I believe that there exist many great practicing teachers, some of who deliberately set out to become one and others who may have never graduated from college but are none-the-less excellent and capable teachers. I would hazard a guess that many readers of Small Farmer’s Journal know more than one teacher who falls within this latter category. My grandfather, and artist and author Eric Sloane, were two such teachers.

Congo Farm Project

Congo Farm Project

by:
from issue:

I was at day one, standing outside an old burnt-out Belgian plantation house, donated to us by the progressive young chief of the village of Luvungi. My Congolese friend and I had told him that we would need to hire some workers to help clear the land around the compound, and to put a new roof on the building. I thought we should be able to attract at least 20 workers. Then, I looked out to see a crowd of about 800 eager villagers, each one with their own hoe.

Portrait of a Garden

Portrait of a Garden

As the seasons slip by at a centuries-old Dutch estate, an 85-year-old pruning master and the owner work on cultivating crops in the kitchen garden. To do this successfully requires a degree of obsessiveness, the old man explains in this calm, observational documentary. The pruning master still works every day. It would be easier if he were only 60 and young.

To Market, To Market, To Buy A Fat Pig

Within so-called alternative agriculture circles there are turf wars abrew

American Milking Devons and the Flack Family Farm

American Milking Devons and the Flack Family Farm

by:
from issue:

On a sunny early September day I met Doug Flack at his biodynamic and organic farm, just South of Enosburg Falls. Doug is an American Milking Devon breeder with some of the best uddered and well behaved animals I have seen in the breed. The animals are beautifully integrated into his small and diversified farm. His system of management seems to bring out the best in the animals and his enthusiasm for Devon cattle is contagious.

Kombit: The Cooperative

Kombit: The Cooperative

We received word of a new environmental film, Kombit: The Cooperative, about deforestation in Haiti — and an international effort to combat it by supporting small farmers on the island.

Livery and Feed

Livery & Feed

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from issue:

A livery stable, for the benefit of those who never heard of one, was an establishment which catered to horses. It boarded them, doctored them, and bred them, whenever any of these services were required. It also furnished “rigs” — a horse and buggy or perhaps a team, for anyone who wished to ride, rather than walk, about the town or countryside. It was a popular service for traveling men who came into town on the railway train and wanted to call on customers in cross-road communities.

NYFC Bootstrap Videos Clover Mead Farm

NYFC Bootstrap Videos: Clover Mead Farm

I couldn’t have been happier to collaborate with The National Young Farmers Coaltion again when they called up about being involved in their Bootstrap Blog Series. In 2013, all of their bloggers were young and beginning lady dairy farmers, and they invited us on board to consult and collaborate in the production of videos of each farmer contributor to the blog series.

Farmrun George's Boots

George’s Boots

George Ziermann has been making custom measured, hand made shoes for 40 years. He’s looking to get out, but can’t find anyone to get in.

Farm To School Programs Take Root

All aim to re-connect school kids with healthy local food.

Expanding the Use of the Heavy Draught Horse in Europe

Expanding the Use of the Heavy Draught Horse in Europe

“La Route du Poisson”, or “The Fish Run,” is a 24 hour long relay which starts from Boulogne on the coast at 9 am on Saturday and runs through the night to the outskirts of Paris with relays of heavy horse pairs until 9 am Sunday with associated events on the way. The relay “baton” is an approved cross country competition vehicle carrying a set amount of fresh fish.

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