Build a Cheap Greenhouse and Save Lots of Money

My cheap greenhouse after it was completed.

A cheap greenhouse isn’t easy to find, especially if you’re looking for a kit to construct. They are expensive! Several thousand dollars isn’t uncommon, and that will buy you a basic structure with plastic, but no vents, fans or controllers to keep the temperature where you need it.

You might as well build your own greenhouse and save money. That's what I have done. I built my own greenhouse and then saved money growing my own vegetables.

You’ll have to build a greenhouse anyway, even if you buy a kit, so you might consider building your own from scratch. It's not that difficult.

You know you’ll save money on groceries with the vegetables you’ll grow, so let’s take a look at how one might build their own greenhouse and save even more. This is my aim here, to show you how I built my first greenhouse. I had no experience, but I was motivated by rising produce prices and my own quest to be more self-reliant.

I started to build a greenhouse out of an old shop in the fall of 2007. I did it for way less than what a comparable kit would cost. It's truly a cheap greenhouse. And, I have much more of a greenhouse as a result.

The original shed was a chicken house. It worked well in that regard, but had so much more potential, so I converted into a cheap greenhouse that supplies plenty of vegetables, even in the winter months. This old shed was used for chickens, ducks, geese, rabbits and who know what else. It had a dirt floor and the place was a mess inside and out, but it worked well for small animals. They never complained about the accommodations.

Here is how my cheap greenhouse started, a poorly built shop.

The shed was built "not bad" many years ago using scrap materials. The walls and rafters were not evenly spaced, and some of the foundation wood was rotting away to the point where it sagged the roof and wall on the north side (see picture above), but not too bad for the structure that would soon be my first cheap greenhouse.

At one time I thought of using it as a workshop, but it was just too small. The best features were electricity and water inside, and its east and west orientation. That was perfect for a greenhouse.

I didn’t want to raze the building because that meant starting from scratch. If I was going to have a cheap greenhouse, I was going to make use of the structure that I had. Besides, I wanted to keep something of what was originally here when I bought the place.

The Project

Instead of demolishing the building, I stripped off most of the walls and roof, braced the walls against wind loads, added some sheer walls. I also added gussets to the roof rafters at the peak, and started to clean up the place so I could paint it white and turn it into a cheap greenhouse.

The cheap greenhouse needed gussets to tie in the rafters, joists and angle bracing.

To the left is an example of how the roof of my cheap greenhouse is strengthened by gussets. They're made of plywood and connect the rafters on each side of the roof. Use a nail gun for speed.

Notice too that angle bracing and joists are tied together with the gusset for added rigidity.

While on the roof, I noticed that the middle of the building wiggled north and south like the center of a hot dog would if you shook it gently while holding it at the ends with your fingertips. Well, this wouldn’t work with the high winds we have here (even for a cheap greenhouse), so I added three diagonal braces running from the peak to the sole plate on the north wall.

Another look at the angle bracing that ties in gussets and joists of my cheap greenhouse.

Above is a look at the angle bracing that runs from the peak to the sole plate. Notice that gussets are installed on both sides of the rafters and the two joists that are parallel to the ground are tied in for added strength.

I anchored the diagonal braces into the gussets near the peak, and tied them into the rafters they passed on the way down to the sole plate. Since the 2 by 4s provide compression (push) as well as tensile (pull) strength, this braced the building well enough. Thankfully I didn’t need diagonal bracing from the peak to the south wall. This would have interfered with the planting beds.

The cheap greenhouse structure was a bit wiggly. It needed diagonal bracing to tie in with the sole plate to provide compression and tensile strength.

To the right is an example of how I tied in the angle bracing to the sole plate. Since the construction of this cheap greenhouse isn't standard, the diagonal bracing didn't line up with the upright members, so I had to shim a bit to make a solid connection to the sole plate.

The north wall and a small strip of the roof were left in place to provide structural support and to allow climbing on the roof to access the top vent. This little strip of roof will also hold the vent piping for a small heater that will help stretch the summer season and take the bite out of an early spring startup.

The photo below shows the narrow strip of roofing left in place on the north side. The vent at the top will be used as an exhaust for the waste oil heater. This photo was taken when the framework was all painted and ready for the plastic glazing to be installed.

Painted frame of the cheap greenhouse showing the narrow strip of roof on the north side that was left in place.

The roof pitch is relatively gentle, so there is a chance of snow accumulation. A steeper roof would help in this area, but I didn’t want to rebuild the structure, just reinforce it so it could be used successfully. Remember, this is a cheap greenhouse so we are not rebuilding it.

The cheap greenhouse has a woven poly roof. Notice that it is stapled in place with a plastic lath that runs down each rafter and over the edge of the building.

If you have something similar that you want to turn into a cheap greenhouse, the easy way to do it is to remodel, not rebuild. If it will work reasonably well without significant modifications, then leave it largely as is and do the remodeling.

If you get into making modifications to the structure that substantially alter its shape or orientation, it isn’t a cheap greenhouse anymore, it is a major and expensive undertaking. This is what you want to avoid.

A hose and a power washer helped get much of the surface gunk off the lumber. There were lots of nails to pull and lots of sanding to do. About 20 gallons of paint soaked into the old dry building frame. It was a lot of work, but I always viewed it as an investment in the future of keeping me fed – a lifetime investment at that.

The Result

This cheap greenhouse project took quite a while to finish. It was several weeks of work because I was doing it for the most part alone. Get a helper and you have about one weeks worth of work. Regardless of the effort, it is all behind me now and I have a nice cheap greenhouse that is 15 by 30 feet with a single layer of ripstop woven poly on a bright white wood frame.

In the winter, it can get into the 70s inside, and in the spring it gets into the 90s. The higher the ambient temperature, the warmer the inside gets when the sun is shining.

Here is a view of the north side of the cheap greenhouse after much of the work was completed.

Having a greenhouse that gets to 90 degrees or more is great for a handful of plants, but too warm for most. Keeping a temperature in the 70s and 80s is perfect for a wide range of fruits and vegetables. I have vents and a fan to help keep the temperature reasonable inside my first cheap greenhouse.

Experience so far suggests that I need to install a few additional vents to eliminate overheating. If they don’t do the job, then I will have to add shade cloth during the summer or a misting system. We have intense sun here, and at over 6,000 feet elevation, the sun has a much greater effect than it does at sea level.

Vents and fans are installed by framing into the walls to take advantage of prevailing winds and venting high temperatures up where the heat rises. There is some electrical work involved, but it isn’t that complicated. If you sit down and figure things out on a piece of paper, you’ll do just fine. Besides, the folks that sell you this stuff are also there to help.

This is the fan that exhausts hot air from the upper region of my cheap greenhouse.

On the right is a picture of the greenhouse fan. It is mounted in a frame near the peak of the building on the east side where prevailing winds won't fight it. The fan is plugged into an electrical outlet, and that outlet is wired as "switched" to the thermostat. In other words, the outlet is only live when the exhaust fan thermostat closes on high temperature.

My cheap greenhouse has an intake vent that opens on elevated temperatures and closes on lower temperatures.

To the left is a picture of the 3 foot by 3 foot vent that opens on elevated temperatures. You can set the thermostat to whatever temperature you like. Framing this in was relatively easy to do. Just leave room to fit the vent frame into the wooden frame that you build. If you fit is too tight, your cheap greenhouse becomes a frustrating greenhouse.

The frame of the vent is held in by 12 screws that to the wooden frame built between the uprights. I didn't have to cut any upright members to install the vent frame, but I did support the framing on top and bottom with additional 2 by 4 lumber.

Below the vent you'll notice a motor that is controlled by a thermostat that closes on high temperature. The motor opens the spring-loaded vent, and when the temperature is reduced, the thermostat opens and the springs force the vent back to a closed position.

Thermostats that control the vent and the exhaust fan for my cheap greenhouse.

To the right are the thermostats, one for the vent and one for the exhaust fan. They are coordinated such that the vent opens at about 78 degrees, and he fan turns on at about 85 degrees. After the temperature drops, the fan stops first and then the vent closes.

Conduits and weather proof seals protect the thermostats from water entry on the top, and all lines are arranged to allow a "drip loop" that keeps water from finding its way into the thermostat, even if it tries to follow the romex cable into the units.

Since there is no wind inside this cheap greenhouse, the drip loops work with the assistance of gravity to direct condensation and water droplets away from the thermostats and to the ground below.

I probably spent about $2,500 rebuilding and painting this cheap greenhouse structure, and outfitting it with all the vents, fan, switches and whatnot required for a successful operation. It was a lot of work, but it was an investment in my future, and it won’t ever have to be repeated. I fully expect the building to last at least another 20 years. I hope I do too.

The only thing that will be a recurring cost is replacement of the poly covering. It is UV protected on both sides, but it only has a limited life. I am expecting 5 years of service (and hoping for 8 years) from this material, but I can’t be certain on that. Only time will tell.

When you need a greenhouse cover, take a look at THOR Tarp. They specialize in custom greenhouse covers, shade cloth and tarps. And, they've been in business for over 12 years. With lots of different materials and options to choose from, I'm sure they can help with your greenhouse project.

Heating the Cheap Greenhouse

Two heat retention systems are installed but only one is operating now. The first system is a 38 gallon stainless steel tank mounted inside one and a half 55 gallon plastic drums placed end to end and sealed. The steel tank acts as a reservoir for heated water that comes from a flat plate solar panel outside the greenhouse. The space between the steel tank and the plastic drum is well insulated from the ground.

This is the barrel that contains the tank and pump used to heat up the floor of my cheap greenhouse.

A pump is plumbed into the steel tank and resides inside a 5 gallon bucket that is attached and sealed to the outside of the plastic barrel. An underground Pex piping circuit lies beneath the walkways of my cheap greenhouse and is connected to the pump and the flat plate solar collector. The whole system is designed to drain back when the pump isn’t running, so no water can freeze during the cold winter nights.

To the left is the heart of the system. The lower barrel can't be seen as it is buried about one foot below the surface of the greenhouse floor. There is a vent shaft and air tube covered with a nylon screen coming out of the top of the system. This allows air to escape and water to be added.

The return line is insulated to keep the water warmer and to reduce the possibility of sunlight deteriorating the Pex piping. The Pex material is not supposed to be installed or stored in the sun, so covering it make sense.

Also notice the black wire coming up from behind the blue barrel. This is a temperature probe that keeps track of the temperature of the tank inside the insulated barrel.

The cheap greenhouse temperature probe reads 106 F as the highest temperture the water has reached with a single solar collector.

Early spring temperatures showed about 41 degrees F, while late spring temperatures showed that the water was reaching 106 degrees F at the highest, using only one solar panel. Such temperatures are not reached in the summer months as the sun isn't oriented as perpendicular to the panel as it is in the spring and late fall.

The system will be covered with a "dog house" to hide the mess and provide a working platform as well.

You'll notice that this cheap greenhouse heating system has a manual switch mounted on the diagonal brace nearby. The manual switch works fine for now, but if I don't turn it off after peak sun hours, the system cools the earth beneath the greenhouse by using the solar panel as a heat exchanger in reverse.

The system will eventually be set up to turn on and off as the sun shows itself and warms a temperature switch. Since the temperature switch will cool in the evening and during cloud cover, the system will make maximum use of the energy from the sun without running warm water through the solar panel when the sun isn't shining.

This is where the Pex piping exits the cheap greenhouse on its way to the flat plat solar collector.

When the pump is turned on, it pumps water through 135 feet of ¾ inch Pex piping about a foot beneath the dirt and sand covered walkways of the greenhouse. That water exists the greenhouse and enters the bottom of a flat plate solar collector where the sun heats it as it rises to the top of the collector. At the top of the collector, it exits and returns to the insulated steel tank where it is pumped through the underground piping again.

Above right is the insulated portion of the Pex piping that exits the greenhouse floor on its way to the flat plate solar collector.

The idea is to store the heat of the sun in the moist earth beneath the cheap greenhouse. This acts as a thermal battery and releases heat slowly throughout the night, to be recharged again during the next sunny day. The system is operated manually for now, but will be automated.

A probe monitors the temperature of the underground steel tank. I have been able to get the tank temperature up to 94 degrees F in March, and at the end of May we have seen 106 degrees F. Obviously, the soil is being warmed, both by the warm water piping and the warm greenhouse.

I have one flat plate solar collector installed now, but plan to add two more and orient them for maximum effectiveness during the dead of winter. With three solar collectors, I can probably reach about 120 degrees in early spring, and that should be plenty of thermal “pressure” to warm up the 45 degree soil in the early spring to promote plant growth.

Single solar panel that heats the water that runs through the floor of the cheap greenhouse.

I am already seeing benefits of the solar panel heating in my cheap greenhouse. Recently, the temperature outside dipped to 27 degrees, and the greenhouse remained at 40 degrees. This is quite an improvement, because usually the greenhouse will be at or just a few degrees above the outside air temperature during the middle of the night since I only have a single layer of film covering the structure.

To get a 13 degree difference in the greenhouse means that there is a source of heat during the night, and that has to indicate the effectiveness of the solar heating system.

I am very happy with the results, and so are the plants that inhabit my cheap greenhouse.

The second heat retention system is not operational yet, but we are getting close. It is 300 gallons of water in the form of six 55 gallon drums plumbed together, with sufficient head space to allow for expansion due to heating. The barrels are plumbed to a pump that will circulate water through a heat exchanger associated with a homemade waste oil heater.

The waste oil heater will heat up the air in the cheap greenhouse and the water inside the barrels. This will provide good lasting warmth in the cheap greenhouse, as water is a great heat storage medium. The system isn’t finished yet, but will be designed as a drain back system and will include a cross connect to the underground Pex piping system. While heating the air and 300 gallon water storage tanks, I might as well heat the soil as well.

The cross connect will also provide me with the opportunity to take advantage of the solar panels to heat the water instead of using the waste oil heater. This will allow me to have a daytime heating source and an option for a nighttime heating source.

Onward to Greater Success

Plants thrive best in warm soil. They tend to care less about air temperature and much more about soil temperature. These heating systems will use moist soil and water for heat retention, and offer the benefit of air heating as well. The plan is to use the waste oil heater on a limited basis and let the water tanks also be a passive solar collector during the summer months.

You’ll be hearing more from me about my solar and waste oil heating systems. They are a frugal way of providing additional heat to the plants that call the cheap greenhouse their home.

Lastly, we use raised beds in our cheap greenhouse. Our raised beds are a bit different than what you might imagine. They are half steel barrels that are about 2.5 feet above the ground. They tend to absorb and retain heat during the sunny days and give off that heat during the night to keep the greenhouse above ambient temperatures.

Steel barrels cut in half form the core of our raised beds in this cheap greenhouse.

This heat retention took some time to show itself as the soil was heating up more slowly in the barrels. As the days got longer in April and May, we started to notice that the temperature differential between the cheap greenhouse and outside temperature became greater. I attribute this to both the solar collector and the raised beds.

As I improve the insulation and heat collection capability of the greenhouse, the lows won’t be so low. As I improve the venting and circulation of the greenhouse, the highs won't be so high. This will take time as I become familiar with the needs of the controlled environment in light of the temperature extremes and sunlight intensity that we have here in Wyoming.

If you build your own cheap greenhouse, be aware that the angle of the roof also contributes to solar gain. A steep and high roof will gather more heat from the sun than a shorter and flatter roof will. Each greenhouse is different.

So there you have it, my first homemade greenhouse. It supports my plan for frugal living that centers on growing my own produce. Greenhouses represent a sizable investment, so this part of my frugal living plan requires that I make investments with a "long view".

Good fortune with your own version of a cheap greenhouse, and may it support your vision of frugal living and good healthy eating.

Done with Cheap Greenhouse, take me back to Build Your Own Greenhouse

Having your own greenhouse is a key to creating viable marketplace alternatives to the ever rising price of produce in the grocery store.

A greenhouse is a great way to grow produce year round, even without additional heat. It's also an excellent way to be better prepared for marketplace interruptions.

With a greenhouse, you're in better control of your food supply in terms of variety, cost, availability, and knowing exactly what's in it and on it.

In this column you'll find links to assets that I find useful when building and operating my greenhouses.

I use this small indoor greenhouse to help get my seeds started. It's lightweight yet strong, and it's a good alternative to a cold frame if you keep it indoors or at least out of high winds.

I own this excellent book, and it's a great reference for those of us involved in greenhouse gardening. I've yet to find a better book about greenhouses.