Greenhouse Heating, by Inda Woods

We now have indoor plumbing and a Wal-Mart, along with the millions of acres of wooded wonderland. Some of our forests are so dense and vast that even the DNR officers have become lost. We are alive with moose, wolf, cougar and black bear, to name a few. My husband and I are in our mid 50s and bought our 40 acres of forest in Michigan’s Upper Peninsula 20 years ago. Can you believe it; we paid only $13,000 for our woods and small cabin? Back then, no one in his or her right mind wanted to live in this harsh, almost Siberian-like wilderness, especially in the winter. It was a time when the only good paying jobs were in logging and mining and we still had a four party telephone system. Many places did not even have electricity. It is crazy how much things have changed in a few short years.

Back when we were settling into our new forest environment, we quickly discovered that the old-fashioned back yard garden becomes a lesson in futility until one learns that Mother Nature owns your butt. You do not do anything in this neighborhood, without her permission. Mesmerized by the warming of your world in early spring and the arrival of the first fawn, the chances are good that you have forgotten who is running the show. By mid spring, dear Mother will send a massive cloud of no see ems to eat out your eyeballs. By late summer, her army of Deer flies and Mosquitoes arrive to finish the job of reminding you that her justice is real.

At the beginning of winter, which can come anytime after the second week in September, Mother Nature unleashes her heavy cloud formations and delivers them in off Lake Superior. By mid-December, cranky, old man winter gets his gears moving and orders his cold winds to storm down from the Canadian arctic. The old guy mixes it up with Mother Nature and together they can dump an average snowfall for the season of 100 to 300 inches depending how close to the pristine, moody, Lake Superior you are. The Upper Peninsula is rich in soil minerals, however most soil for growing crops is horrible. A soil PH of 7 is a great find and is much treasured.

My reason for setting the stage is that one of the biggest obstacles of living up here will be fresh food. Having the ability to hunt and loads of dehydrated food is great but we need live, fresh food too. Therefore, the question is; how do you grow food in such an inhospitable climate and rotten soil? There is very little farming in the upper peninsula, and only one or two families make a living from strawberry u-pick farms, a couple of blueberry farms and a select few potato growers, that is it. Notice the crops mentioned like an acidic soil?

Our mission has been to grow a years worth of food without spending a shipload of money. Our ideal system would be a sturdy greenhouse and a low or no cost heating unit. Solar is almost useless during the time that we would need it the most, so we crossed it off our list. In the beginning of our homestead, we built a makeshift greenhouse out of windows the neighbors had donated to get them out of their garage. It was fun to build and use. Glass is wonderful for use as a greenhouse but the wooden frames eventually rot due to moisture and mildew. It served us well for almost 8 years but the needed repairs exceeded our budget, thanks to a lot of wind and a falling tree branch.

With paper and pencil in hand, we figured out the size of the new greenhouse we would need and the amount of cash we could afford to spend. We wanted to be able to extend the season by two months in both directions since our growing season barely makes 90 days some years. (Some of the old timers say that they have seen it snow at least once, in every month of the year.) It is also not out of the realm of possibilities for the temperature to fall to -40 or -50 on a clear night, although normally it only gets 20 below. There is just no growing anything from November to February here either, even if you had megabucks to spend on heating a greenhouse or had a good south-facing window. There just is not enough sunlight to do the job without very expensive artificial lighting. People living in Maine for example, do not seem to have the problem we do with dark cloud cover for those 3 months of the year. During December and January, it is totally, 100% dark at 4:30 P.M. (central), in the afternoon, another reason we won’t even try to grow in that part of the winter.

We began saving some our limited dollars and eventually were able to purchase a corrugated polycarbonate greenhouse, 16ft. X 20ft. (It is smaller than what we had hoped for, but money being hard to come by we settled on what we could afford.) I want to kiss the person who invented this type greenhouse. I was in love! It was delivered the second week of March during a blinding snowstorm. Needles to say, we did not get it up until June and much bad language from hubby. For the first couple of years we were unable to use it from late October to late April. We could only extend the season a couple of months in the spring and a few weeks in the fall, we wanted more. It needed heat to take advantage of what this beautiful polycarbonate building had to offer. After a winter’s worth of research, we came up with a plan. Using ideas and experience from several authors, we put something together that is relatively inexpensive to get started but holds up well and works fabulously. Most of it is made from scrap or junkyard salvage. For the very first time, I grew beautiful sweet potatoes. (These critters are delicious but space intensive. I just wanted to see if I could do it.) Here is what we did.

Before we put up the polycarbonate greenhouse, we had 3 yards of gravel brought in and dumped. At the time, we were only interested in making a level spot for the greenhouse. The spot we had chosen had a great south facing view but had a sizable slope to it. The hill had too much of a slope to put up a greenhouse without added material. The dump truck left a mountain of gravel right where we wanted it. We hauled and leveled the huge pile by hand which took about three full days. The instant the area was leveled and smooth, we unboxed the greenhouse parts and got things sized, measured and eventually, up.

When the time came to put in some sort of heating, we decided on a modified version that we found in a book called “Solviva”, by Anna Edey. Anna had a grant to build her experimental greenhouse, so she was able to have solar panels and all the gizmos and gadgets that go with solar as a back up heat. Too expensive for us, but what she covered in the book that we used was the example for a wood fired device she had in the center of her massive greenhouse. We used her idea and modified it to fit our greenhouse.

Parts list;
55-gallon metal barrel cut in half, long ways.
An old metal bed frame, taken apart.
Angle iron, one eight footer should be enough.
Steel plate 26” x 40” 1/8 inch thick. Thicker would work but this is what we had on hand.
4” chimney pipe, purchased~ not very expensive.
Two small hinges, taken from a barn door.
Woodstove gasket
First, we found an old 55-gallon barrel and cut it in half-long way. Make sure the barrel did not have toxic material in it. Next we hand dug a hole in the back center of the greenhouse, deep enough to fit the half barrel. I think the hole was about 20 inches deep, 45 inches long and 30 inches wide. You will need room to lower the half barrel into the hole and backfill around it.

Next, we found an old metal bed frame and dismantled it. We kept only the sidepieces, the two pieces that hold the mattress. Hubby then cut two lengths to fit either side of the half barrel, since the sides will be weight bearing. Next, he found some sturdy angle iron and cut four of them slightly longer than the width of the barrel; these will sit on the bed frame sidepieces. Fill in any gaps with wood stove gasket. (The first year we had this up and running, we put the barrel level with the gravel as that is what Anna did in the book. She also used longer angle iron across the barrel and sunk them into the backfill before laying down the sheet metal. Her model was much bigger due to the size of the space she was heating.) Next, hubby cut a sheet of steel plate ½ inch longer and wider than the half barrel. Looking at the steel plate long ways measure in 14 inches and make a cut on that line. On this, you will put two small hinges before placing it on the top of the barrel. The hinged flap becomes the door where you load the wood into your new in floor wood stove. Our design worked great for the first year but the second year we had such heavy snowfall that when the snow melted it filled the greenhouse with water. We have found that if our half barrel sticks up from the gravel about two inches or so, the spring melt will not leak into the barrel and put out the fire.

The first in-floor woodstove we made: Hubby cut a 4-inch hole in the end of the half barrel, and this was where the original chimney connected. It worked fine for the first few years but the connecting elbow filled with creosote, which clogged the pipe. We had to dig up the pipe from the backfill to clean it. Since then we made a new stove and put the chimney on top through the steel plate. It is much nicer but limits the space on top of the unit. The chimney should extend 2 feet above the surface of the greenhouse roof. It is better for draft and heat and smoke will not damage the plastic roof material. The re-enforced steel plate is used because once your in floor woodstove is finished and ready to fire up, you will want a waterproof container sitting on the steel plate. Once your bucket or barrel is filled with water and is heated, it acts like a pan of water on the kitchen stove. The heat and moisture add comfort back into the room. In addition, what we have found is that the gravel around the woodstove stays warm for a long time even when there is no fire in the stove. This area makes a nice place to put seed starting flats. The bottom heat is perfect for little sprouts to come alive. Even when it is minus 4 degrees outside and I will have little pale green life making their first debut against the rich black soil.

Here we are, the second week in December and we have just finished the last of the salad fixin‘s. We served a robust tossed salad for our Thanksgiving meal of Butterhead lettuce, green and red spinach, Tah Tsai (spinach mustard), Pac Choi and Kale. Once the last of the salad greens are harvested, it is time to clean the greenhouse and put her to bed for the winter. About the second week in February, I start the seed flats with new potting material and lovingly place the seed into their new home. Depending on weather conditions, how cold nighttime temperatures, I may let my seed flats stay inside the cabin for a week longer. Hubby cuts an extra cord of firewood in the fall just for the greenhouse. I do not want to use it all right away, so I may wait to fire up the greenhouse. In addition, I have better control of germinating temperatures when the seedlings are in our cabin at super cold night temperatures. About the end of March, I can use the greenhouse floor for germinating.

Another maneuver I used before the woodstove was installed, that turned out well, is making a greenhouse inside the greenhouse. I made a small wooden frame about 24 inches tall X 48 inches long X 48 inches wide and covered it with plastic. Place this mini greenhouse over the growing seedlings. Cover with a blanket at night to keep the daytime soil heat from escaping. It is surprising how efficient it is. If you do not mind using a little electricity, you can place a small electric heater in there too. I have started spinach and mustard greens and kale in September, placed them under the mini greenhouse in the greenhouse raised bed and had them spring to life when there was enough sunlight to make them happy. They were in a kind of holding pattern during the dark months.

Money is an issue

No money for a fancy greenhouse? Not a problem. For the price of a few feet of 6-mil white/clear plastic, you can have a nice greenhouse and can still use the woodstove idea. We experimented this year with an almost no cost way to extent the growing season.
We had some scrap 2 x 2s which we used to erect a frame. We also had on hand, scrap fencing material, some galvanized cattle fence and some chicken wire fencing. Whatever the material you use, it needs to be bendable. After we were satisfied with the frame construction, we mounted the fence over the framework and stapled to the 2 x 2s. Next came the plastic sheeting, which was also stapled onto the 2 x 2s. Because it can get quite windy in the fall and winter, I used regular clothesline rope to tie it down. We drove 6 stakes into the ground, three on either side of our new greenhouse. Next, I took the rope and went back and forth over the plastic knotting the rope around each stake as we went until all the rope was used, leaving enough to tie the end to a stake.
We have not yet, put a woodstove in this plastic covered greenhouse, but there is certainly no reason why you couldn’t. I would recommend, however, that you use a section of plywood to mount the chimney through the roof. The heat coming off the chimney can wreck havoc with plastic. Our plastic covered greenhouse sits in the garden where we previously made a raised bed. For this winter, I placed over wintering perennials in it. It held up very well through all the nasty windstorms we have had this fall. I was very happy with this setup.

You can see pictures of the in floor woodstove and the wire and plastic covered greenhouse here.

Some key reference books from our library:

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