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In Search of a Low-Cost Greenhouse

Lori DunnA greenhouse has always been on my list. You know the list I speak of, everyone has one. It is the mental list that we all keep of things we would like to have someday. That “someday” came for me when my husband suggested we go ahead and put up a greenhouse.

I was extremely excited with the thought of being able to get a jumpstart on our gardening, and experimenting with different plants and flowers, but I also knew we needed to be economical about it. We couldn’t afford to incur a large expense in the construction of the greenhouse, or in the heating of it later. This sent me on the path of the internet highway to do some research. As you can imagine, I found lots of information on all kinds of greenhouses. There is everything from prefabricated kits that come with everything you need to instructions on building your own greenhouse out of many different materials. What I found that caught my attention the most was information on a thermal mass greenhouse. This type of greenhouse uses energy from the sun to store heat, and then release that heat at night when it is needed. Energy from the sun = free, just the right price!

According to the information I found, many things can be used for the “mass” to collect the heat and energy from the sun. Anything that retains heat would probably work. Some of the items listed included soil in raised beds, wood, block or brick foundations, concrete, or even the floor of the greenhouse. But the most effective and least expensive thermal mass is water! Again, water = free! It didn’t take much for me to decide that a thermal mass greenhouse was the way to go for us. But how would we store the large amounts of water that would be needed? The recommended amount was about 2-3 gallons of water per square foot. Apparently, a common practice is to store the water in containers along the back wall of the greenhouse, or use 55 gallon drums filled with water to support the benches in the greenhouse. In one instance I read about, someone had used the method of water in barrels under their benches. They said it kept the temperatures in the greenhouse above freezing except on the very coldest nights. On those nights, they used a very small space heater as a supplement to keep the temperatures up.

My husband and I have a great setup to use this type of greenhouse. Our basement wall is underground on three sides. The fourth side is exposed and faces in a southeastern direction. We came up with a plan to use the face of the exposed basement wall as the back wall of our greenhouse. It would face the right way to capture the heat from the sun. The block wall in the back could store some of the sun’s energy, and we would also use barrels of water on both sides of the greenhouse with planking across the tops of the barrels as bench tops. The wall we wanted to put the greenhouse against has a window into the basement. I thought we could also use this to our advantage. We heat our home with a woodstove in our basement. This keeps our basement nice and warm too. If we built the greenhouse around that window, then on the coldest nights, we could open the window and use a small fan to pull some of the heat from the basement into the greenhouse as a supplemental heating source. I was excited to test all this and see if it would work!

Building a thermal mass greenhouse

We began construction in March. We decided to make the greenhouse 8 feet deep by 24 feet long. My husband was the brains behind all the measurements. He came up with all the figures and sizes for making the correct cuts, and attaching the greenhouse to our basement wall. With some help from our son, my greenhouse soon started to take shape. It wasn’t long till we had a frame in place.

Constructing a thermal mass greenhouse part 2

We knew that it was also important to have a way to let some of the heat escape when the temperatures got too hot, so we put a window in on the parallel wall to the door opening on the shorter 8-foot wall. This would correspond with the predominant wind flow here, so we could open the window and door and have air move through.

Constructing a thermal mass greenhouse part 3

Finally the framing was completed. Now, we were ready to wrap the greenhouse with plastic. This was the one thing that we would later realize we should have done differently. We wrapped the greenhouse, roof and sides, with the plastic. Dancing in the streets, laughter, and applause … MY GREENHOUSE WAS READY TO USE ... well, almost!

Constructing a thermal mass greenhouse part 4

We still had to get the “thermal mass.” This is where my wonderful son-in-law, Deron, comes into play. Where he works, he has access to large, 55 gallon black plastic barrels. The company he works for gets them full of alcohol for sterilization purposes. He was able to get the empty used barrels for me for free! I LOVE FREE! We set the barrels along both the outer and inner long, 24-foot walls, and filled them with water. We then used planking a crossed the tops of the barrels to act as my bench tops. Now, I was ready to start planting. Since we were already into March, I wasn’t sure if we could really accurately determine how the greenhouse would do in colder weather, and I thought I was getting a late start in getting seeds in the ground to be able to transplant for planting time. It turned out that timing for transplanting was perfectly fine by starting my seeds in March. For the most part, everything had plenty of time to sprout and grow to size for transplanting into the garden.

Thermal mass greenhouse

We installed one of those thermometers in the greenhouse that has an extra unit that we could put in our house. This way we could monitor the temperature of the greenhouse from inside our home.

Seedlings waiting for transplant to the garden

On average, the temperatures inside the greenhouse stayed a good ten degrees or more than the temperatures outside, overnight, with no extra heat source. As soon as the sun would come up, the temperature would raise substantially higher than outside. There were only a couple of nights that we opened our basement window to the greenhouse, to let in a little extra heat.

I consider this greenhouse almost a complete success. The one thing that was a problem for us would not be a problem for most people. When we bought the plastic to wrap our greenhouse, we did not take into account the fact that we have free roaming poultry! Here is an interesting little tidbit for you. Ducks and chickens LOVE to poke holes in plastic! Till the end of the growing season, the plastic on the greenhouse was pretty much done for! This is simply what I call a live and learn experience! We now need to rewrap the greenhouse with plastic. We will either use a higher grade of plastic, or use plastic sheeting. That will be determined by cost right now. Either way, we are planning a very large fenced poultry enclosure, so we shouldn’t have to worry about the same thing happening again.

All in all, I would recommend this type of greenhouse, but, beware of ducks and chickens!

8/17/2015 10:54:37 AM

Actually, once you get the plastic issues with the chickens addressed - they are actually great to have in the greenhouse due to the high BTU output they give out. Your greenhouse sounds like a smaller version of the one that Anna Edey built on Martha's Vineyard in the 90's. She was a great visionary and practitioner of sustainable living and builing. Her book "Solviva" is well worth a read!! I wouldn't be without it. Although, it's been a lot of years since she began, and advancements have been made - her core principles remain solid. You can check it out on as well.

sergiy polovenko
4/16/2012 11:02:54 AM

It is better if you put your greenhouse to the south facing wall. Itwont give you much from the north side

4/6/2009 12:52:39 PM

Hello Nebraska Dave! Ahhh yes, seasonal work. My dad has a wood shop in which he now makes his living.( We used to operate a small sawmill till we had to shut down due to the economy.) During this time of year, my dad makes all kinds of wooden flower planters that get sold to greenhouses all over this state, and a few others. These early spring months when the growing season is just getting under way, and Easter and Mother's Day are just around the corner are very busy for him. Very much the same for orchard growers too, when the fruits start to ripen and need picked. Lots of people are needed for long hours to get the fruit picked, but when it's all picked, everything sort of comes to a halt. And oh what fun to try and put plastic on a greenhouse in windy conditions! I didn't know it was the responsibility of the plant supplier to erect shelter for the plants at these stores! I always assumed the store itself did that. My own greenhouse plants are coming along nicely. I have Asters, Snapdragons, Petunias, Delphinium, Zinnias, Sunflowers, Nasturium, pansies, Parsley, Tomatoes, zucchini,and cucumbers all through the ground and I am still waiting on Peppers, Watermelon, Heliotrope, Rudbeckia, and Jacob's Ladder to germinate. It is so much fun to check the progress every day to see how things are coming along and what may have poked it's head through the ground during the overnight!

nebraska dave
4/6/2009 9:47:46 AM

Lori, I’m really getting my Springtime greenhouse fix this year. My operation at home is to small to warrant any kind of greenhouse. I decided to help out a friend and become a seasonal worker for a company out of Kansas that delivers plants to local stores here in Nebraska. Little did I know that seasonal work is no where close to being part time work. Seasonal work is 10 to 14 hours a day for duration (three months). I supposedly accepted a job as delivery driver for 12 stores but didn’t know that included the job of building the parking lot displays and corrals for the store's temporary garden centers. The first delivery day found me delivering in rain changing to snow with hail and wind. The poor greenhouse coddled pansies probably wondered where in the world they had come to. Anyway back to the greenhouse. Four of these stores have a temporary greenhouse Quonset in the parking lot. First the frame work was erected. Then three of us unfurled a piece of plastic to cover the frame that was about 100’ x 75’. I can imagine we looked quite humorous wrestling the big sail, that was flapping in the breeze, up and over the frame. It was quite an experience for me, that’s for sure.

3/30/2009 1:47:32 PM

Hi Lori, thanks for the link and the information on your experience since we have been hoping to avoid much digging because our site has seasonally high groundwater. The deepdug foundation will be omitted and we'll try another alternative, maybe a short berm to shelter the lower framework of the walls, and a drainage rivulet to keep the water away from the walls. At least we don't have chickens to worry about. Best wishes.

3/29/2009 5:10:25 PM

Hi MJ! Our greenhouse does NOT have a deep dug foundation. It is set right on top of the ground. I can only tell you that ours did not have any problems with heaving. I can't however promise that heaving would never be a problem. I am by no means an expert here. As for the roof, we didn't have problems with that either, but we didn't have a lot of snow this past year, and my plastic was torn(from the ducks and chickens, not the snow)so we really didn't get an accurate idea of how it would do in deeper snow. One of the sites I looked at did call for a steep pitched roof to allow the sun to penetrate better during the winter months. The link to that site is: Our greenhouse keeps temps above freezing most of the time. There were a few very cold nights that we had to open the window to our basement to allow more heat into our greenhouse to keep the temps up, but only a few. you will probably need some form of extra heat for those very cold nights. I hope this answers your questions, and good luck with your greenhouse!

3/29/2009 4:50:29 PM

L. Danby, Thanks for the great idea! We have actually already answered this problem because we have put up a large poultry inclosure. My plastic poking ducks and chickens can no longer get to the greenhouse! ;^)

3/29/2009 1:24:35 PM

Hi Lori, this is exciting for us because we're just begining to work on a small barn and the idea that we could orient it and make the southeast wall plastic sheeted to have a greenhouse/barnlike addition to our micro-agriculture designing is perfect timing. It's also quite useful that you're in the same sort of temperate/cold area as we are in Ohio so I was looking at the construction details in your wonderful photos. I couldn't see any special deepdug foundation to get the bottom below frostlevel and wondered if that was just the angle or timing of the photos. Or is it that the exposed ground and the solar heated thermal mass does prevent frost heave??? Which would be unpleasant in any structure. The other puzzle I was wondering over that your research may have uncovered is the roof. I'd think the low profile would be good for wind safety but maybe complicate the snowload problem in ordinary housing design. Did the experienced authors in your research say that the warmth that prevents freezing in the plants' area would prevent snow from accumulating on the roof and make the snow able to run off without freezing into a sheet of ice or worse??? We tend to be conservative about these sorts of things and maybe that's not appropriate for a greenhouse though we wouldn't like to have to deal with problems that some might dump on their insurance, which we do not have. We're self-insuring and take responsibility for avoiding risks. Hope these questions are easily answered. We always love easy answers when possible. Best Wishes.

l danby
3/27/2009 10:29:03 AM

Your chicken problem is easily fixed by putting a half sheet of OSB (2 x 8) or some cheap wood around the bottom of the greenhouse.

3/19/2009 8:06:09 AM

Hi Valerie! I hope the greenhouse works as well for you as it does for us. We have re-wrapped it, and I have started my tomato, pepper, cucumber, zucchini, and a variety of flower seeds. My daughter is coming today to help me get some more flower seeds started. I LOVE having a greenhouse!

3/18/2009 8:16:59 PM

Lori: What a great idea for an inexpensive greenhouse! I have tried to turn my back porch into one, but it is too cold and loses heat quickly. I am a new Texan (having come from Washington State with a shorter growing season) and it's my first time gardening down here! My husband has tilled up a 1/2 acre garden spot (or shall I call it - preparing the soil for a crop?). This idea of a thermal mass greenhouse is a good one. Here in Texas it gets very hot in the summer (and we've had 80+ weather several days now already) and I could see how warmed up water will keep it warm through the night. Thank you for sharing! Valerie

3/12/2009 7:38:18 AM

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3/11/2009 9:46:42 PM

wondering if it would be possible to sell subscrip.... at my place of business...... Bluegrass"Pik-n-Barn" 931-788-2751..

3/8/2009 9:42:29 AM

Nebraska Dave, You are correct, I do a lot of canning and freezing. I use a water bath canner to do my canning. I don't own a pressure canner, but it is an investment I might make in the future. I do my canning in two ways. I use the "normal" method of submerging my jars in a water bath for whatever time is appropriate for the food I'm canning. I also do what my grandma calls "open kettle". With this method, you don't submerge your jars in water to process at all. This method can be a bit more tricky because if not done properly, the jars won't seal. Basically this involves having your sterile clean jars very hot, packing them with whatever you might be canning, at a boiling hot temperature, and then putting your hot flats and lids on the jars. As the jars cool down, they seal. Only certain things can be done with this method. I can tomatoes, tomato sauce, salsa, dill pickles,red beets,apple pie filling, cherry pie filling, and grape juice.There may be a few more things added to that this year! I freeze the rest of our bounty. It is possible to can low acid vegetables with a boiling water bath, but the processing time is so long that I don't do that anymore. They would be much easier to can with a pressure canner. Filling the freezer can be risky if the power goes out, but we have a generator for just such instances. I've had a lot of luck finding canning jars at yard sales around here. I've even gotten boxes of them for free because people just want to get rid of them! I'm glad that you're getting back into these things now that you're retired, and flattered with your complements. It is very fulfilling to " Do it yourself"!

nebraska dave
3/7/2009 10:21:46 PM

Lori, size of operation makes absolute sense. My paltry couple six packs of vegetable plants and the same for flowers would hardly justify the expense of a greenhouse. Some times the challenge of the building project over shadows my sense of use afterward. However having a big garden brings me to another question. You must preserve food if the garden is big? In the past I have with some degree of success preserved garden produce and at one point in time I had dozens of jars and a 21 quart pressure canner. Those days have long past and all the supplies to preserve the bounty of my harvest have been given away. I mostly canned tomatoes and sweet corn when in season. I just don’t trust freezers as the last couple years, power outages here have increased as well as the outage length. I personally just liked the taste of canned produce more than frozen and I didn’t have to worry about freezer burn. I even tried making catsup once and amazingly enough it turned out pretty good. We have road side produce stands and we have a farmer’s markets during the summer months to fill our pantries. Now with the life changing event of retirement last year, I have a desire to get back to the basics of simple living. If I remember correct the acid in tomatoes makes them pretty safe to preserve in a water bath canner. I do have a huge stainless steel cook pot that I can use for the preservation of tomatoes. What other vegetables can be preserved in a water bath canner? A friend and I go to thrift stores on a regular basis. The last excursion netted my first 18 Ball and Mason jars. We happen to hit half price Friday at one Thrift store and I bought 14 pints and 4 quarts at 14 cents a piece. It’s not a real huge amount of jars but it’s enough to get me started again. Grit magazine and your blog, Lori, has brought me back to my roots. Thank you so much and be encouraged to keep up the blogging.

3/7/2009 5:14:02 PM

Nebraska Dave, I know exactly what you're talking about. Does it really pay to go to all of that trouble in the end, when one can go to their local greenhouse or garden department and buy what they need without all the hassle? For me the answer is simple. It is very much worth the trouble. If I were just getting a few veggie plants to put in my garden than, probably it wouldn't be worth it. We put out a very large garden, and I have a lot of flowerbeds, so I would buy lots of veggie plants,seeds, and flowers every year. I would usually end up spending quite a lot. I also LOVE gardening. I get joy out of the planting, sprouting, transplanting, and watching everything produce beautiful flowers, or yummy veggies! Another thing that I love with the greenhouse is I had extra plants that I didn't really have room in my garden for, so I supplied lots of family, friends and neighbors with plants as well, and they were thrilled to get them. I came to the same conclusion as you in other areas mind you. I was very much considering getting milk goats so we could have our own milk. I'm no stranger to this as we had milk goats in the past, and I know the work involved. I have determined that I can just as easily buy my milk, because I don't have the extra time to devote to the care and work that would take! Maybe some day...

3/7/2009 4:55:31 PM

I have to make a correction to this entry. The correct size of our greenhouse is 8x24, not 8x12. Don't quite know what I was thinking when I gave those measurements! Cindy, Cost was the issue that put us off as long as it did before building a greenhouse. This was a very cheap way for us to go because we already had the rough lumber. One of the perks from being a sawyer at one time! Our biggest expenses here was the plastic and screws to put the thing together. Even the window was given!

nebraska dave
3/7/2009 4:19:20 PM

Lori, this is an excellent article about the marriage of gardening and do-it-yourself ingenuity. I do like to do-it-myself. Free is a beautiful thing isn’t it? The recycling aspect of free does have its merits as well. If I might I would like to share some thoughts and pick your brain a little. The question for me would be to greenhouse or not to greenhouse. In my younger years if a fleeting thought passed through my left sided logical male brain and it tickled my interest, adrenalin would flow and I would immediately fall into the full speed ahead “Git er done” mode. This formula made for many disasters. As the exuberance of youth passed and gray haired wisdom took over, I learned to contemplate and plan a little more before launching full scale into a project. Many times have I bought seeds and tried to nurture them from birth to adolescent seedlings, but I just never really seemed to come up with a plan that worked for me. At the end of eight weeks, the store bought seedlings always looked so much better than my coddled tall leggy sickly looking plants. They ended life in the compost pile to be used later to enrich the soil for the store bought plants. Lori, I understand the satisfaction of doing something for pure enjoyment and accomplishment. It’s that same deep down good feeling for me that comes when a home project has been completed. Lori, is this a similar thing with a greenhouse? Is it about the pleasure to bring seeds to full producing maturity? Or are there other benefits to having a greenhouse? In my old logical left-sided male brain spending six to eight weeks to grow plants that I can purchase at the market seems like a lot of time spent for little gain. Lori, please don’t miss interpret any of the ramblings of an old geezer. I’m just really trying to decide whether a greenhouse would be a good thing .... for me. HELP!!

cindy murphy
3/6/2009 5:52:35 PM

Wow, Lori...I am sooo envious! I've always wanted a greenhouse too, but the expense of the pre-fabbed or kit models have kept me putting it off. I've gathered materials for a couple of cold frames, and thought I'd go that route. Granted, I never did an extensive Internet search for greenhouse information.....but now I don't have to! A thermal mass greenhouse sounds like the way to go for us. Thanks for the ideas!