Heating the Greenhouse in Winter

What follows is 15 years of tried and true serious greenhouse heating and growing. 

We live in Michigan's Upper Peninsula, the most hostile place that I know  for growing above ground vegetables. I have witnessed frost on my precious garden in July and complete ground snow cover in September. Most years our frost free days are between the end of May and the second week in October. But in all reality old timers have told me they have seen snow in every month of the year at one time or another. So to say the climate here is unpredictable could be a considerable understatement. We in Michigan's U.P. are at the mercy of the cold Canadian air catching a ride on earths jet stream deliberately gliding over the warmer water of Lake Superior. Together they form a dense cloud cover and enjoy a good laugh while they dump lots of lake effect snow on us. Absolute darkness comes at 4:30 in the afternoon starting in November and lasting until about the second week in February. I think depressing is the word you are looking for, eh?

I don't even try to grow anything between November and February, so when the warm February sunshine finally breaks through the cloud cover it gets my growing juices flowing.  I wake up the greenhouse by firing up an in ground wood stove that my husband built. Such a clever guy! We work really well together, I drew out a rough design and he put together my design out of materials we had around our homestead. But I can't take credit for this in-the-ground wood stove entirely, however. I found a greenhouse stove similar to what we built in a book called *Solviva* How to grow $5000,000 on one acre, written by Anna Edey published in 1998. On page 78, in the section on heating she describes her stove but no pictures. So we did the best that we could meshing her description with our knowledge of wood stove operations. 

Our greenhouse (16' X 20') is poly-carbonate double walled and definitely not air tight. Before the snow comes I take a 4 foot tall roll of plastic and walk it around the whole inside of the greenhouse at the floor level holding it in place with magnets on the supporting pipes.This is similar to what the Indians did inside their Tee Pees for winter insulation. This plastic is taken down in the spring and carefully rolled up for use again later.

Your green house will need to have a dirt floor for this to work. 

 

(To the left of the picture you will see one of our hens. Our chicken coop used to butt up next to the greenhouse, so when there was nothing growing in there one side became a chicken run. Our hens loved digging in the bed and left fertilizer in return. It was a win win.)

 Start with a metal 55 gallon barrel, both ends need to be still with the barrel. Cut the barrel in half long way. Dig a hole where you want your stove, slightly larger than the size of the barrel, and deep enough to allow about two inches of the barrel to stick up above the dirt line. Snuggle your half barrel carefully down in the hole and replace the dirt in the spaces around the barrel. Tramp lightly where you back filled, add more dirt if needed. Next Hubby placed metal pieces across the half barrel to help support the lid and anything that we set on the top plate. Then he added fireproof gasket around the rim of the half barrel to make an air tight seal with the top plate, to keep smoke from escaping and filing up the greenhouse.

Hubby had this 1/4" thick metal plate hanging around, slightly wider and longer that the half barrel. (Neither one of us can remember where that piece of metal came from) It was perfect! Next he measured 18" and cut a straight line across it and added two hinges. This now top plate has a door to load the wood. Now it needed a place for a chimney, so he cut a round hole in the metal plate at the opposite end to accept the chimney pipe. On our first try, the 4 inch diameter chimney was just too small. The small chimney pipe didn't allow for acquit air flow so the smoke didn't draw up the chimney like it should have. We tore that out and made the chimney hole bigger settling on a 6" hole and chimney pipe. The air flow draw was much better which allowed for a hot a fire for about 5 to 6 hours before needing more wood. With our knowledge of how wood stoves work, we determined that a larger than 6" diameter pipe may have let too much precious heat go up the chimney and heat the outdoors. Also, due to the 6" stove pipe and almost air tight design of this stove we needed to prop the door open for awhile when first starting the fire inside. After the fire gets going and there are a few coals in the bottom, the door can be closed all the way. There were days however, when the air was thick, heavy or raining outside or no breeze we left the loading door open a crack most of the day to allow for the smoke to draw out the chimney.

 

We made the chimney pipe stick up in the air a good two feet, mostly to assure hot smoke or debris wouldn't damage the poly carbonate roof of our green house but also for catching a good breeze for smoke draw.

Because the chimney pipe can get quite warm a bigger hole is cut in the roof and metal was added to hold the chimney pipe secure. We chose to put the chimney close to the back corner. With the extra distance we helped support the chimney pipe with wire anchored around roof supports.

There is good news about a stove like this and there is bad news. The good news is that I just loved this in ground stove! The barrel usually lasted 3 full seasons before the need to be replaced. Once the stove had been in use for a few days, the ground in the greenhouse became warm. I could then sprout my seeds on the floor next to the wood stove in February and March. I was simply in awe of all my tiny sprouting vegetables at minus 5 degrees outdoor temperature! And keeping the ground damp allowed for good humidity in the growing sunshine and all night long. 

The bad news is that the fire burned itself out and cooled the greenhouse during the early morning hours. It didn't hold a hot fire all night. The stove needed refueling. One of us loaded the stove at about 10 or 11, before going to bed and either Hubby or I would have to go out at about 3 or 4 in the morning to add more wood. We kept a sheet of paper tacked to the back door to record the time we added wood to the stove in case we woke up at different times. The other would know he/she had put wood in the greenhouse stove. Our night temperatures in February and March can reach 20 below during the dark hours. However, the green house seemed do just fine as long as we didn't let the stove go out. If this were a survival situation, we had discussed, we could put a cot to sleep on out there in the winter to ensure that the fire never went out and our food supply would be safe from the freezing cold night time temperatures. 

Yes, we are eating salad fixin's from the green house in late March, zucchini in April. One year I was able to get a small crop of sweet potatoes, in the U.P.!

I hope this little bit of how-to gets your growing/survival juices flowing. If so, please like, share and subscribe. Comments and questions are always welcome.