“Breathe in. The air is rich, humid, fragrant and full of life, warm on your face. It’s comfortable. What is it about a greenhouse or sunspace that feels good to almost everyone? It’s more than just stimulation of the senses. It goes deeper, further back. The tropics were the womb of human life, and the greenhouse is a connection to our origins.” – Shane Smith, in Greenhouse Gardener’s Companion
Having a greenhouse can extend your growing season, allow you to start plants earlier and perhaps allow you to grow food that couldn’t survive in your outdoor garden. We started our greenhouse in 2012. I will share what we have, how it was built and some tips we learned along the way.
We inquired about building our own greenhouse or having someone help us at the local commercial nursery/greenhouse. She suggested this retired couple that lived in a nearby town that built greenhouses. Their 10’ x 20’ prefabrticated greenhouse unit was perfect for us. The boards on the bottom frame of our unit are treated 2” x 6”. All of the other wood was regular untreated kiln dried lumber.
Note: The next one that I buy or build will be built out of all treated lumber, since the door frame and window frame have experienced some decay with the weather.
The hoops are made of 1-3/8” galvanized top-rail  (like used for chain link fencing). The window is an aluminum storm window with screen, 30” x 44” in a 2” x 4” frame. The door is 36” wide by 75” tall and made from 1” x 4” lumber inside a 2’ x 4” frame. The total height of each end (door end and window end) is 86” measured from peak of greenhouse roof to top of 2” x 6” base. Galvanized pipe was used for the bracing on the front and the back. You will need the 20’ x 50’ 6ml poly sheeting  to build the 10’ x 20’ green house.
This poly sheeting is rated for four years, but as you can see, we are going on the 7th year. It is showing some age and has some dirt and mildew staining. I am going to try to gently clean it with my power washer this spring on a warm day and see if I can remove some of the staining without hurting the plastic.
To bend the top-rail into hoops, Colorado Metal Worx has a neat product, and a video that shows how it is done .
There are other companies that offer hoop bending tools, like www.hoopbenders.net  You will need a 20’ piece of top-rail to make a 10’ wide greenhouse. These top-rails will fit inside the 2” x 6” frame and are attach by U bolts to the wood to keep them in place. This design is much stronger than the plastic PVC tubing so many videos on YouTube show. Purlins are the horizontal pipes that hold the hoops in place, as you can see, they used 3 purlins on my greenhouse. They are attached to the hoops by galvanized straps and bolts/nuts, they also used band clamps made for 1-3/8” fence tubing.
Looking closely at the first hoop at the end by the door shows a wooden strip attached to the hoop, this is a kerfed strip of wood that the poly sheeting will be stapled to. Only the ends have this wooden strip. This PDF from hoopbenders.net  shows how kerfing the wood works to bend it. Of course, soaking it for days also helps you bend the wood. The construction is very similar to mine and shows you how the poly sheeting is attached. (Pages 33-39 show the kerfed wood).
They brought the greenhouse frame (without the poly sheeting attached) on a flat bed trailer. We lifted it off together and determined our exact placement. Next, we worked to attach the poly sheeting, very similar to the above-mentioned pdf. We used a white batten tape  instead of folding so much to staple the poly-sheeting in place.
Ready for Wind Storms?
Living in the Ozarks, we get our share of high wind storms and an occasional tornado. So, they told me how to stake down the greenhouse to keep it from blowing away. I cut a 6’ t-post in 4 pieces. I purchased 4 large U-bolts that would hold a muffler on. I drove the t-post stakes next to the wooden frame on all for corners, and drilled holes thru the 2”x6” and attached the stakes to the frame with the large U-bolts. During high wind, we always close & lock the green house door. So far, we have lost trees in wind storms, but not the greenhouse.
We used dirt to make the floor inside the greenhouse mostly level, and then used cedar mulch for the flooring, which we add to yearly. We dump mulch around the outside to make sure there are no holes near the base to let in cold air. I used concrete blocks to hold up the raised beds I made from 2” x 4” and treated plywood (drilling holes in the plywood will allow extra water to drain out if you over water your plants). I should have spent the extra money and bought 2” x 6” to make it a little deeper.
We have the raised beds on either side of the greenhouse, pushed all the way to the door, and have a handmade table with shelves in front of the window, which stores tools, the big box fan, and the electric milk-house heater. For electricity, we just used a contractor grade heavy duty extension cord and ran it from the shop to the greenhouse under the base and attached a power-strip onto the leg of the table with some zip-ties. In the next section, I will discuss how we used our greenhouse.
Growing in a Greenhouse
Okay, you have your greenhouse. Let’s get started growing! I read in Shane Smith’s Greenhouse Gardner’s Companion  about using a water drum. Having a large 39-55-gallon container filled with water, acts as thermal mass and can help moderate both high and low temperatures in the greenhouse. He recommends using water drums to hold up benches, tables or raised beds. I really didn’t want to do this since we had plenty of free concrete blocks to elevate our beds. I found a 50-gallon water barrel  with spigot and a lid, at local farm supply for less than $50. This has worked perfectly.
We fill the barrel with water and try to keep it 3/4 full at all times during the spring thru fall. During the winter, I fill it up before the hoses are put away, and that lasts til spring, if we have a warm spell, I top off the barrel. It is handy to have a watering source in your green house. Okay, what to grow?
Getting Your Soil Ready
I have noticed that the soil in these shallow beds, needs rejuvenating each time you plant a new crop. So, mix up a batch of your favorite topsoil/garden soil/favorite manure and replace each time you plant. I do use Miracle Grow, the type with granules that you mix with water. I don’t replace all the soil, but probably about 70%, I put the ‘used soil’ in the compost tires. (You do have tractor tires in your yard for composting, right?) Tractor tires make great planters . You just use a chainsaw and cut the side wall lip off the section that faces up, and you are good to go!
Now we grow potatoes, onions, asparagus, sweet potatoes, and garlic in ours. I am getting sidetracked, so back to the greenhouse.
We have good soil and are ready to plant. I like to plant cool weather crops in late winter, like February here in the Ozarks, which is about two months before you would plant outside. The weather can change fast around these parts, so we could have snow tomorrow and be 60 degrees just two days later. That’s just how it is around here, it’s not man-made climate change, it has always been that way. It’s whether the wind blows from Texas and the Gulf of Mexico, or down from Canada and the Rocky Mountain States.
Greenhouse Temperature Regulation
So, we have to figure out how we’re are going to regulate the temperature in the greenhouse. Whenever your greenhouse is above 85 degrees in the winter or above 90 degrees in the summer, it’s too hot for maximum plant growth. To keep things cooler, we faced the door of the greenhouse (the narrow section) toward the most intense sunlight, for us; the southwest. So, the greenhouse gets morning sun from the East hitting the larger section, and the smaller section during the hottest part of the day with the more intense sunlight. We use the box fan in the open window and keep the door open (with a bungie cord) to cool down the greenhouse when it gets too warm. We also used a sun shade  most of the year over a portion of the greenhouse to keep it cooler. Our friends up north may not need one.
We have a thermometer with a remote sensor that sends a signal inside the house, so we can monitor the greenhouse temperature from the kitchen window. Keeping it the right temperature can take some work, having the temperature sensor inside can remind you that you better open the greenhouse door, the East sun is heating things up in a hurry!
Some cool weather plants that can tolerate some light frost that we have planted are; spinach, Swiss chard, lettuce, broccoli, chives, onions, radishes, sweet peas and carrots. Some herbs are: rosemary, fennel, dill, and cilantro. If you are planting to grow and harvest in the greenhouse, select varieties that have a shorter number of days to harvest. Remember when the sunlight is less, like in early spring, fall and winter, the plants grow slowly. Things are going great, your lettuce and spinach is coming up, peas are growing, and the weather man says the polar vortex is coming down south. Oh no! Time to fire up the milk-house utility heater .
This little bugger can save the day. Check the perimeter of your greenhouse, make sure your chickens didn’t scratch all that mulch away from the base and you have holes where cold air can enter. We use the box fan (with the window closed), on low behind the milk-house utility heater and blow warm air the length of the greenhouse. Use your thermometer with the remote sensor (you did buy that, right?!) so you can sit in the kitchen by the wood stove instead of tromping out to the greenhouse every hour to see if your lettuce is gonna make it.
When and What to Replant
Alright, your plants survived the polar vortex and genuine spring is finally here. As things heat up, we have to make a decision whether we are going to keep these plants and replant them outside or let them go. I have started our tomato plants from seed in the greenhouse and transplanted them into the garden or pots. For seeds like that, I use the little plastic trays that you see in the nurseries and grow the plants in there to replant.
If you have never grown plants from seeds in a greenhouse, then I suggest that on a nice day you take those trays of seedlings out in the sun for a few hours, especially if there is a nice breeze. This will make the plants stronger. I also use the box fan on low, to create a breeze during the hottest part of the day, if I leave the little plants inside the greenhouse. Going from the regulated air of the greenhouse to the garden can be a shock, so I try to condition the plants before I replant them.
Occasionally we have had pests, once we had to deal with aphids attacking our tomato plants. For this we used a soapy water solution every few days until they all died. You have to get under the leaves and really soak them with the spray. Introducing plants from another greenhouse, a mail order company, or gift from a friend can introduce pests into your greenhouse. Carefully examine your new plants and rinse them with water to make sure you are not introducing a new pest into your greenhouse. Keep your beds clean, pick up your dead leaves, pull up dead or dying plants, isolate plants in poor health, keep the air moving, being careful with new plants. Those are all good tips to keep pests out of your greenhouse.
I also use quite a few fabric plant containers (the big ones with handles) to grow carrots and some onions. When the greenhouse is too warm, I move these fabric containers outside. Eventually, for us, usually about mid-late June, it is just too hot for the greenhouse, and we close it up until late summer.
Once the nights start getting cooler, late August or early September, I replant lettuce and spinach to eat in the fall and winter. I have learned you can’t wait too late to plant, those seedlings need decent sun to get started, once the winter sun and short days are here, growing comes to a crawl, so plant at least two months before that winter sun comes. We had some spinach this year make it all winter long, despite giving up and not heating the greenhouse. So, some crops like spinach are very hardy in cold weather.
I hope this helps you decide if a greenhouse is right for you, I know that we have certainly enjoyed ours!