I had a dream once. - I am standing in a vast green summer field looking down into the earth. The ground is a large glass roof in the shape of a cross. I can see tropical plants and seedlings flourish in the warm, light flooded space beneath. There is a sacredness to the space that is breathtaking. - I woke up and remembered both the beauty and impossibility of the vivid dream. Plants growing happily underneath the earth? Can't be.
I met my farmer friend Verena a few weeks later and my dream came up during a conversation. She said, “Yeah, it's called an earth-bermed greenhouse. You can build such a thing and it's been done before.” Really? Well then, I thought, let's make a dream come true.
It took me a while to find the person who was willing to embark on the adventure with me. My friend Jesse, a natural builder who is always on the lookout for new territories to explore, gave in to the calling.
What was supposed to take a couple of months at the most turned into a year long journey, as he ended up not only building a practical and functioning earth-sheltered greenhouse, but a piece of green architecture that feels and looks like the sacred space I dreamed about three years earlier.
We used the basic building plans from Mike Oehler's book The Earth Sheltered Greenhouse for the layout and material list.
An earth-bermed greenhouse is best build into an already existing South facing hill with full sun exposure. We started clearing shrubs and fallen trees from an area close to the house matching these conditions and decided on a 16x16 foot growing space. Oehlers's plans include digging out a 3-4 foot deep “cold sink “ at the South side of the greenhouse. A space that is designed to allow cold air to settle into at night, rather than hovering over your tender seedling that are growing in the work space.
The soil in our area has a lot of clay and does not drain water well. We added French drains around the whole outside perimeter to redirect the water flow around the structure. French drains are trenches with perforated pipes that are wrapped in landscaping fabric. The trench then gets filled up with crushed #4 stone and covered with top soil.
Next we started digging the 3 foot deep post holes. Even with the drainage system in place, the holes immediately filled with water and we decided to add PVC socks to the 6x6 pine posts to make sure they would not be exposed to moisture in the ground, preventing them from rotting. After setting the posts the holes where back filled with cement.
Next, the walls went up. We found a good deal for rough red and white oak boards which we planed. Pine or hemlock would have worked as well, but we found a reasonable source for oak and we knew the walls would look beautiful when oiled later.
Oak does not do well when exposed to moisture, especially red oak, and we had to come up with a solution to protect the outside of our walls from the constant moisture in the ground that would surround them. We used a pond liner to protect the outside of our walls but also had to make sure that no moisture would condensate in between the walls and the rubber liner.
We had just replaced a cedar shingle roof on our house and used a product called cedar breather to provide airflow in between the cedar shingles and the plywood it gets nailed into. It allows the shingle to dry faster and prevents it from rotting, extending the lifespan of the shingle by many years. We decided to use the same product between the greenhouse walls and the pond liner to ensure airflow and avoid condensation and water damage.
We used a heavy duty pond liner and wrapped it around the whole structure, making sure not to rip any holes, and stapled it to the top of the walls.
Then we had to protect the pond liner from ripping during the back-berming process. We covered the pond liner with cheap sheets of plywood to make sure not to rip any holes into the rubber. Once the crushed stones settle against the plywood, the plywood can safely get wet and rot away over time.
We choose SunTuff for the roof. It's an affordable polycarbonate corrugated roofing material that does not gas off chemicals, has a decent R factor and comes with a 10 year warranty against UV degradation.
We looked into double pane roofing material as well but the costs were astronomical in comparison and we felt we found a good compromise. To make the space feel more open and connected, we added a large safety window glass at the South side which provides a beautiful view into the surrounding woods and the feeling of being inside the cockpit of Starship Enterprise.
To ensure ample airflow and cooling for the seedlings during hot days, we added two large automatic vents to the South facing front and three vents above the North back wall.
There is no access to electricity close to the greenhouse and we contemplated a solar powered automatic vent system. Adding a solar panels would have been too expensive and we found Univent automatic vent openers instead. Univents are oil piston operated vent arms which automatically open when the air inside the greenhouse heats up and close again when the temperature drops at the end of the day. You can fine tune the opening and closing temperate by turning the pistons a half or full rotation further into the threads. These turned out to work really well and the growing space is self ventilating without the need for an additional fan.
We used all natural Tung Oil and citrus solvent to seal the walls and trusses. These do not fume any harmful chemicals into the space when the greenhouse heats up.
The whole structure was protected with cedar shingles and back bermed, first with #4 crushed stone to provide drainage and prevent the clay soil to push and heave against the walls, then with soil.
Large stones form the surrounding area were used for the floor to collect even more heat during the day and give it back to the space at night.
55 gallon barrels filled with water and stacked against the sun exposed North side act as heat sinks and balance the temperature in the greenhouse when they give their heat back to the space at night. We found recycled food grade plastic drums at Capital Containers in Albany for $18 a barrel.
We used cedar to build the doors and a window on the West side to let a little bit of extra afternoon sunlight flood the growing space.
Instead of using the typical cement blocks and wood pallets for the seed tray tables we decided to build hanging tables to protect our seedlings from rodents – which worked really well. We can also unhook the light weight cedar frames easily and use the space for other types of events, such as herbal medicine classes in the fall.
Later in the summer, when all herb seedlings have fletched and left our green mother womb (as we call her) the greenhouse is turned into a drying space for herb harvests. We keep the same hanging tables and simply lay fiberglass mosquito screen on the tables, then lay the fresh herbs out on the screen and let them dry with plenty of air circulation from the vents. When the herbs are dry we simply roll up the screen and carry the dried herbs out to the garbling station (garbling means separating leaves and blossoms from stems and other unusable parts).
The outside of the greenhouse provides for a a lot of new growing space. The whole front is South facing with full sun exposure and now hosts many new sun loving and low growing herbs.
The East side was bermed high and gets a lot of morning sun. We added key holes to the planting area so the whole herb bed can be reached easily without having to step onto the soil and compacting it.
Stone steps where added on the West side to hug the window and Jesse burned two beautiful sacred geometry patterns into the cedar doors, the Flower of Life and the Kiss of Venus.
And just to top it off, the whole space is covered with sacred geometry carvings and details that keep reminding you that you are not just standing in a greenhouse, but in a living breathing growing space for sacred plant medicine, just like in my dream.
There she is. Mother womb for our green medicine babies. My dream come true and a immeasurable gift from a very dear friend of mine that means more to me than words can say.
Thank you, Jesse.
With endless gratitude,
Susanna Raeven - Raven Crest Botanicals