It has been a while since we sharing an update on our greenhouse build progress. Not much was accomplished during the heat of the summer. Now that fall is here we have taken advantage of cool weather and got busy with this project. The structure is up, the end walls are built and all of the double wall plastic is up and secured. The blower motor that inflated the canopy is installed and operational.
What’s left to do to the greenhouse
What do we have left to do with this greenhouse? The side curtains on our greenhouse need to be installed. This Zimmerman High Tunnel kit has curtains that secure at the bottom and drop down from the top to vent excess heat. After the side curtains are up and operational, the door needs to be built, covered with plastic and installed.
Once the door is on we need to bury an electrical line pulled through conduit. It will provide the power to the for the inflated fan and the fan that will blow air for the heat sink. Once the power is run to the greenhouse we will work on the grow boxes and making the heat sink operational.
The grow boxes
We have all four of them built and pushed to one side of the greenhouse. They need to be placed, spaced out, leveled and secured in place with stakes. An application of preplant will applied to the soil inside the grow boxes. Then they need to be topped off with a mixture of sand and sawdust. After mixing in an application of weekly feed and preplant with the sand and sawdust the grow boxes will be ready.
The two grow boxes down the center of the greenhouse will have the a-frame structure built to allow vertical gardening. That can be built after the seedlings are in and in the warmth and comfort of an operational geothermal heat sink greenhouse.
What’s left for the heat sink
So far we don’t have any more greenhouse build progress to report on the heat sink portion of this project. But it’s on our list of things to accomplish. Once the greenhouse is buttoned up the heat sink is our next project. The pipes on the inlet side of the heat sink will be bundled together and cut at the same height above the ground. The fan that will move air through the heat sink will be mounted on top of the barrel that will be our manifold. That barrel will then be partially buried over heat sink pipes.
Watch the video update of our greenhouse build progress
This video is part 7 in our YouTube video series on our geothermal heat sink greenhouse build. If you haven’t already done so, please consider subscribing to our channel.
We are excited to be starting the planning process on a geothermal heat sink greenhouse build. We will build this geothermal heat sink greenhouse to allow us to grow our own food year round. It would be wonderful to be able to grow frost intolerant crops like tomatoes during the dead of our winters. Without question, we will be able to grow hardy and moderately hardy crops all year inside this greenhouse.
More details about our green house plans
For the heat sink we will use 48 inches of rock that will be placed under 24 inches of topsoil beneath the greenhouse. We will use a 4 inch thick Styrofoam insulator 6 feet tall around the perimeter of the rock. The foam board will prevent the heat held in the rocks from being drawn out into the cooler soil outside the foot print of the greenhouse.
During the day, the warm/hot air from the peak of the greenhouse will be drawn down through duct work and a fan and be pushed out near the bottom of the heat sink. The 4 inch pipe that is used below the ground will be perforated to allow the air to escape. The air will move up through the rock to a second set of pipes, transferring the heat from the air and into my thermal mass. The air will enter the second set of perforated pipes and be pushed into the greenhouse.
During the night when the green house temperature drops below that of the thermal mass heat sink the system will work in the opposite manner. Cool air from the green house will be pushed through the rock and pick up heat. As the air returns to the greenhouse it will be warmer, keeping the greenhouse temperatures warm through the night.
The high tunnel kit we selected
For our high tunnel kit we selected a 20 x 44 foot kit from Zimmerman’s High Tunnels. They use 14 gauge steel that is 2 3/8 inches in diameter. It is a little larger diameter than most kits we found while searching for kits. Zimmerman’s is a few hours drive from our home and we will be able to pick it up to avoid freight charges.
The drainage pipe we are using
For this project we will be using 4 inch corrugated drain pipe, often referred to as drain tile. All of the pipe that will be horizontal will be perforated to allow air to escape and enter the rock. Anything installed vertically will not be perforated to ensure the air makes it to our heat sink. This is what our 4 inch corrugated and perforated pipe will look like. We will buy it in 250 foot rolls for around $98
There will be two layers of this pipe, ten each, the will run the length of the greenhouse. Both will be buried within the rock 3 feet apart. One group will be 6 inches from the bottom, the second 6 inches from the top. The top and bottom layers will not be connected.
The pipe near the bottom of the rock heat sink will be connected to the fan that draws heat from top of the greenhouse. We intend to use a 55 gallon plastic barrel as a manifold to bundle all 10 of the pipes together. With the fan mounted on top of the barrel it will be able to push air through all 10 pipes.
The ten pipes 6 inches from the top of the heat sink are also perforated and will direct the air blown in from the bottom up and back out into the greenhouse. All of the pipe laid horizontally will be perforated.
Airflow pattern through the heat sink
Air will flow down to the bottom of the 10 perforated pipes at the bottom of the heat sink. The air will be pushed through the perforations and up through the rock to the second set of horizontal perforated pipes. The air enters through the perforations and is directed back up and into the greenhouse.
Where each pipe terminates inside of the rock heat sink we will place a cap designed for the the corrugated pipe. When we connect the perforated and non-perforated pipes we will use a an external connector designed specifically for the corrugated pipe. All unions will be wrapped in a tape intended for drain tile and to be buried.
How we came to decide on our greenhouse dimensions
As with all our gardening here, we will be utilizing the Mittleider Gardening Method in our geothermal heat sink greenhouse build. There will be 4 grow boxes inside this greenhouse that are 18 inches wide and 30 feet long. We want plenty of room to move and work in our greenhouse in additional to being able to do all our seedling production in the same place.
We have settled for an overall length of 44 feet. This will allow a 5 foot walkway at both ends of the grow boxes. At the far end of the greenhouse we will do our seedling production. We intend to build a 4 foot bench along one wall for seedling stuff and storage of gardening equipment. Ultimately there will be batteries here and a charge controller for the solar panels we want to install.
For the width we are going with 20 feet. It was tempting to go wider to add a 5th grow box, but that would have increased the final cost significantly. The added cost for the greenhouse itself wouldn’t have been horrible. But the additional gravel requirements combined with the other costs for excavation and materials would have significant. And I can grow a lot of food in just 4 thirty foot beds using the Mittleider gardening method.
Considering snow load and high winds
A twenty foot wide greenhouse is pretty strong and able to stand up well to wind and the weight of our Missouri snow. We don’t get much snow here so this allows us to save a little money because we don’t need W-trusses. If we were to go wider it would be smart to spend the extra money for W-trusses with our kit. W-trusses for the kit we selected would have been another $500.
While the heat sink and geothermal combined makes sense, we haven’t yet seen it work. We don’t yet know how it will truly work during our winters. If it doesn’t work and allow us to grow year round a larger system will have been a waste of money. We will start with a smaller system and see how it performs. If it works well and inexpensive to operate a larger unit that would allow us to sell to our local community might be a good business venture.
Removing trees before building
Before we start this project there will be several trees to remove. Doing this will prevent shading on the greenhouse and the root system from taking over the ground under the greenhouse. Removing trees close to the greenhouse will prevent a tree from falling on the greenhouse and damaging it.
There are about 5 trees that I want removed from the vicinity of the build site. Two of the trees are west of the site and will cast shadow on the greenhouse if left in place. One tree is massive, an old black locust, that could potentially drop limbs on our greenhouse. The roots from this tree could also end up under the greenhouse. We prefer to avoid the possibility of any of those problems and will remove the potential entirely.
There are a few additional trees that are to the north of this geothermal heat sink greenhouse site that I want removed. They don’t pose any immediate threat to the greenhouse, but I’d like to remove them now and ensure no trees will ever fall on the completed greenhouse and damage it. We will remove them now to avoid the possibility of tree fall damage entirely.
Goal to have the greenhouse off grid
After the greenhouse is completed and in operation we would like to start getting the greenhouse “off gird”. We will monitor the energy usage and design a solar system that will meet our needs. On the end of the greenhouse under the seedling tables we will build an enclosure for the charge controller and batteries.
Through rain collection off our nearby home into a cistern we will be able to water our greenhouse. We have enough annual rainfall that we can easily collect enough water for our needs. Ultimately we want to use an automated sprinkler system for a lawn to water the 4 grow boxes inside our greenhouse.
Goals for monitoring the geothermal heat sink greenhouse build
A secondary goal for this geothermal heat sink greenhouse, is the ability to wirelessly monitor the temperatures of the greenhouse,. Additionally, outside the greenhouse and the ground temperatures of the heat sink. Ultimately allowing others to view current temps and historical data would be nice.
I’ve not yet researched the options of products that will allow this. We do plan on placing a piece of PVC during the build that would allow a temperature probe to be dropped into the heat sink material. The PVC will be relatively inexpensive, we may add two to allow temperatures to me monitored at the top and bottom of the heat sink rock.
Almost ready to start excavation
We have all the materials except the styrofoam for the heat sink on hand. As soon as we can schedule the delivery of the 125 yards of rock we can start the dirt work, weather permitting. Our goal is to have the heat sink portion completed by the end of February. The greenhouse portion we hope to have completed and ready for seedlings mid March.
We will be documenting this project with photos and video, be sure to check back for updates of our progress.
Why I don’t like a 4 foot grow boxes in a Mittleider garden
I’ll be honest here, I don’t like 4 foot wide grow boxes. They’re popular and you will see all kinds of articles and videos where they are recommended. They require too much bending over of the gardener for my liking. For a Mittleider garden I think they’re generally a mistake.
It is difficult to tend to stuff in it and you can’t reach from one side to the other. This becomes particularly evident when things are grown vertically. Reaching towards the middle of the box to prune or harvest from a mature plant is near impossible. Sure, you can push through and get it done but you risk damaging plants. you could even knock off nearly ripe vegetables.
The top of these tomatoes in the picture below are a little more than 3 feet apart. I can only prune and harvest easily by going down each side of my grow box. Growing these tomatoes in a 4 foot wide grow box would prevent the easy access necessary to properly care for our plants.
Are there good uses for 4 foot grow boxes?
There are indeed. First, if you’re on a very tight budget yet determined to have a grow box the wide grow boxes will work. For the cost of two 18 inch wide boxes you can build one 4 foot box. But if you’re on a budget I’d highly recommend growing in your own soil.
The only time I might recommend a 4 foot wide grow box in a Mittleider garden is for growing potatoes. We have heavy clay soil here in Missouri. Our grow box dedicated to growing potatoes allows them to sprawl and makes harvest a breeze. It is isolated from the rest of the garden and is used only for potatoes. In this picture below we grew sweet potatoes last year.
What size grow box do I prefer?
That’s easy. An 18 inch wide grow box is ideal, particularity for vertical crops in my Mittleider garden. We built these grow boxes in our in the garden green house.
If you cant find a good source locally you can use equine pellets sawdust. In a Mittleider garden the sawdust is used to fill seedling flats or even entire grow boxes.
Ideally you would have access to free sawdust from a sawmill and don’t need to go through the added expense of buying sawdust. If you’re only going to start seedlings a single bag of pellets would last a long time. It also wouldn’t be cost prohibitive. To fill grow boxes would take a lot more sawdust and would quickly become expensive.
If you are considering using equine pellets sawdust to fill a grow box I’d highly recommend that you consider soil beds. They can grow food equally well despite your soil condition while being much cheaper.
How to go from pellets to sawdust
The process of taking pellets and turning them into usable sawdust is easy. All you need to do is add water with a good watering wand to soak everything well. As the pellets absorb water they will expand as the binding agent used a glue dissolves.
adding the pellets to a container that will allow the excess water to drain will make the entire process easier for you. Our wheel barrow has a crack and allows excess water to escape.
If you do not have a container that will allow water to escape try adding water a little at a time until all the pellets are damp. Try turning the pellets with a shovel to ensure everything is wet.
Where and what pellets to get
As the name implies, these pellets can be bought at business catering to horse people. Another source is at business that sell hardwood pellets for homes heated with pellet stoves. Those hardwood pellets are fine and any wood type except walnut will work. The pellet stove pellets can be bought in bulk and can often be bought cheaper by the bag than equine pellets.
The hardwood pellets intended for heating homes is often only carried seasonally and may not always be available. They may also be bought at discount in the spring as they’re no longer needed.
Watch sawdust being made with equine pellets
In this video you can watch equine pellets expand roughly three times into sawdust once it becomes wet. The process is quick and only takes a few minutes.
We have green beans ready to go into the garden, it is time for transplanting seedlings into our Mittleider garden grow boxes. They show a little overall yellowing, so after they are transplanted we will give them a corrective treatment of Nitrogen.
It’s time to transplant green beans in the first grow box for our fall garden. Referring to the Garden Planting Details sheet on page 237 of the Mittleider Gardening Course book, we will plant our bush beans 3 inches apart. It also shows us that we need to plant two rows in our 18 inch grow box.
Tips on transplanting properly
Always avoid handling the seedling by the stem. If you accidentally break the stem you will kill the plant. Instead of the stem, grab the plant by the leaves as shown in this next photo.
I have not yet made the tool for marking grow beds and boxes for transplanting so I enlisted the help of the girls to get our 3 inch spacing.
Do you see the yellow color in the beans we just transplanted above? They are showing symptoms of a nitrogen deficiency. They are in desperate need a correction for a nitrogen deficiency.
Our quest to be self reliant and grow a healthy garden