Poor Man’s Greenhouse

Regina Anneler
16 Min Read

Winter has almost set in, and on most homesteads, vegetable production has come to end with the exception of cabbage, carrots, and other cold-hardy plants that can handle the milder winter weather in some areas.  Veggies like tomatoes, cucumbers, peppers, squash, and eggplants have become a memory for most homesteading gardens at this time of year.  This poor man’s greenhouse, however, makes an exception… if you have used a little ingenuity, planning, and some good old sweat and effort, then these summer-friendly vegetables may just be available to you all year, regardless of the winter chill by building a greenhouse from old windows.

Hoop houses are easy to build and are great for growing in late fall or early spring because the plastic coverings help to deter the cold a few extra weeks.  However, they just cannot hold enough heat to grow much in the deep long-lasting chill of winter.  This means that if you want winter vegetable production your options are very limited for potential means to grow plants.  Greenhouses are usually a pretty expensive and sometimes massive undertaking, but build a greenhouse does not necessarily have to be.  Purchasing a pre-made greenhouse is a major investment that many people just can’t afford to do.  Even if purchasing a pre-made greenhouse can fit into someone’s budget, it is not the last of the expenses involved in having one.  Even greenhouses require some type of heating for the winter months in order to ensure the health of the plants grown within one, which prevents many people from considering them as an option to keep up their garden production in the cold months.  But there is another option; depending on how your homestead is set up, there might be a way to build and heat a greenhouse that would fit within the constraints of a limited budget.

Last winter, after our production levels dropped during the cold months, we made up our mind that we would need to find a way to continue a steady vegetable production for the next winter, so we started planning how to accomplish this goal.  Windows: plain old everyday windows—people replace windows all the time, so what happens to the old windows?  They are often discarded as garbage or sold as used for a decent price.  Windows let the sun shine through, meaning they are a principal feature of and a key piece in constructing a greenhouse.  We made a deal in the spring to trade some of our products made on the farm for a dozen or so old square pane windows in various sizes.  They were not insulated, though it would have been even better if they were.  But even though they did not come insulated, we knew we could make these old, plain windows work for what we wanted.  We looked into many different design plans that we found out on the web, which was great to help with ideas… but none were a real fit for us.

poor man's greenhouse. You can Build a Greenhouse Using Old Windows.

We knew heating could and would be a major issue when temperatures drop below that freezing mark come winter.  Add in the fact that we sell extra produce at a year-round farmer’s market, this just increased our need to grow the vegetables that only the heat and sun-loving plants produce.  Those type of plants would never tolerate temperatures in the low 30s or below.  There were many plans out there for building a self-standing greenhouse, but every single one of those would require a propane heat source to keep the building warm enough in winter to grow the types of vegetables that we needed.  The cost of propane would be way too much to make this an affordable option in our case.  The experience of heating our home taught us that propane as a heat source is often very expensive if the cold stays for any length of time.  However, a couple of years ago, we installed a large woodstove that now heats the entire house all winter long.  The best part of that is we cut the wood we use here on our homestead so the only cost is our time, labor and chainsaw operation cost.  We mulled around the idea of heating a greenhouse with some other type of heat, but electric alone would be just as expensive as propane if not actually more so.

 Then we got a wild, wonderful idea: the greenhouse could be made like an add-on room to the house.  We had a wooden-frame back porch right off the south side of the house, with a sliding glass door in and out of the house.  This door also happened to be directly across the living and dining room from the woodstove.  In the winter all we would need to do was to leave the glass door open to the house so as to share its heat with the greenhouse.

poor man's greenhouse. You can Build a Greenhouse Using Old Windows.

This positioning made it the ideal location to construct the greenhouse in.  Because the sun rises in the east and sets in the west, the longest side of a greenhouse should always be facing the south or southwest.  This is in order to take maximum advantage of the sun’s energy for the needs of the plants.  There were a few problems that we would have to deal with in order to convert this porch into a greenhouse, but we had the start of a plan.  In our case, the porch is elevated about 2 feet above ground so the first issue was to build a wood frame skirting around the porch to prevent snow or ice from getting underneath it.  Then, we had to cover the floor with Styrofoam insulation.  We placed rubber stall mats on top of that.  The mats not only help with insulation but they make it easier to clean any spilled water when tending to the plants.

greenhouse windows

The windows that we traded for were not all the same size, so the building of our greenhouse was similar to building a puzzle; we had to make each piece fit together in order to make a whole room.  We started by seeing where certain windows would fit, then built a frame around the windows.  It was a kind of backward way to go about the construction, but in our situation, it made sure we could use each size of window that we had.  We set posts on each corner that all the windows fit between, then ran rafters out from the side of the house, just under our home’s roofline.  We purchased clear 2.17-ft x 10-ft Corrugated Polycarbonate Roof Panels for the top.  We built the walls straight because our floor was elevated and our roof at an angle.  The roof was angled partly because we had to continue the water flow from the roofline of the house, but also it helped to maximize the solar potential.  If you have a stronger foundation option than we did, the wall of your greenhouse room can be built at an angle as well as the roof.  Angled glass is frequently used in passive solar design because it increases the amount of solar energy coming into a greenhouse.  Angling the glass can cause overheating in the summertime if other precautions are not taken, but in the winter months, a greenhouse requires as much solar input as possible to work effectively.

greenhouse windows, poor man's greenhouse. You can Build a Greenhouse Using Old Windows.

The clear panels do let a lot of sun in the top, but in our case, we insulated it by placing bubble wrap in between each rafter on the inside and covered the wrap with clear plastic sheeting.  This helps to soften the light coming in the roof but does not deter so much light as to keep the greenhouse from working correctly.  This helps us to keep a regular temperature in the greenhouse.  To make sure we had a good seal where the panels met our framework, we used Polyethylene Solid Roof Panel Closure Strips that fit snug to seal out the weather from slipping under the roof panels.

Our next step was to make sure that any windowless areas left in our framework were fitted with the same Polycarbonate panels we used for the roof.  These were cut to fit the openings with a heavy pair of industrial scissors.  Any small gaps or sealing issues were solved with a simple can of spray foam insulation.  In the summer, the temperatures inside the greenhouse can become extremely hot, so we need a way to vent the greenhouse.  The windows that we used were not able to be opened.  They were placed solidly within the framework, so there was no way to vent these.  Therefore we had to be creative; we built a wooden screen door entryway into the greenhouse from outside and built a matching one on its side acting like a window in the center of the south-facing wall.  During the summer, just the screen wire is enough because it allows the greenhouse to vent and the temperature doesn’t drop low enough to be a problem.  However, winter was a different story; we needed the sun to come in these two doors for the greenhouse to work correctly.  We decided the best way to accomplish this was to screw the Poly-carbonate panels on the outside of the screen doors in the winter.  When it is cold out, the sun still shines through and they can be easily removed again in the summer.greenhouse plants

When the outside was completed, we began work on fixing the inside to be useful as the space for the plants that we wanted to grow.  We placed some shelving in the room, but if you do the same, you need to make it very open shelving with high clearance between the shelves.  This is so the light will still be able to reach all the plants.  The southern side where most of the light should enter by shouldn’t have very much obstruction if at all possible.  In our case, we placed benches to have a raised level and then a floor level of plants.  If you plan to grow plants that climb or vine you need to figure out a way to provide support for them.  The tomatoes we planted like to vine and climb; we made this easier for them by placing cables tied to hooks in the framework of the walls.  This allowed us to have room to move around in the greenhouse while still providing support for the plants literally growing between the cable lines.  We also placed a couple of grow lights where we felt shadows fell early in the winter months so as to make sure the plants in that area were receiving adequate amounts of light each day.greenhouse plants

In the center of our greenhouse, we placed a rack with plastic guttering mounted on the railings.  The upper rails allowed for great sun-exposure and the racks were on wheels, which means we can move them to allow extra room when and where we might need it.  The lower rails did not allow for enough light to reach the plants, so we planted cucumbers in these and dropped plastic netting down the racks so that the cucumber vines could attach to the netting and grow securely.

Knowing the current temperature when growing in a greenhouse is very important.  We purchased a thermometer that has a two piece unit so that you can take a reading inside and out and get the readout for both locations in comparison.  We can walk to the doorway and see the current temp in the greenhouse and in the house proper, allowing us to decide just how well the greenhouse temperature is holding.  In the warmer months, when the temperatures can get really high inside the greenhouse, it is important to have a way to help move the air because the venting alone won’t always be enough.  We took an adjustable house fan and mounted it on the upper part of one wall to help move the air and keep the temperatures a little more regulated.  Experience taught us that it worked better mounted up high than being down low on the ground where the plant growth could block the overall airflow.  For cold months, we did end up placing a small infrared heater in the greenhouse but we have only had to turn it on in the worst of cold nights to help supplement the heat coming from the wood stove in the living room.

Currently, it is December and we have eggplants, peppers, tomatoes, and cucumbers growing well.  As a matter of fact, the eggplants are doing better here than they did outside all summer.  I have to admit it is really nice in winter to be able to step out there and pick whatever I need to for cooking without ever going outside.


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