How to Build a Wallipini
First off, you may be wondering what a wallipini is and the answer is simple. A wallipini is an in ground or pit greenhouse. Yes, I said an in ground greenhouse and this old technology is based on the Aymara culture.
The principle behind a pit greenhouse is to use what nature gives you to heat the greenhouse. As sunlight enters the greenhouse, it warms up the soil and rock that is inside the greenhouse. In doing so, raising the temperature above what the ground temperature is naturally.
While there are a lot of details involved when it comes to building a wallipini, the directions below are just a general guide to creating your own pit greenhouse.
Before you dig the first hole, you will need to observe your environment and what you have to work with. You will need to create a rectangular hole that is 6 to 8 feet deep. To capture the most sun, you will need to face the longest part of the rectangle toward the winter sun. If you live in the Southern Hemisphere, the direction you will need is north. If you live in the Northern Hemisphere, south is the direction you need.
Another factor that you will need to consider is where your water table is located. The wallipini will need to be placed above your local water table.
The last thing to consider is what is growing around the proposed area. While it is a great idea to place your pit greenhouse in a barren area, this may not be possible. If this is the case, consider areas without trees. This will eliminate damage to the wallipini from falling branches. On the other hand, if you must have trees make sure that they are deciduous in nature. In the spring, when the tree is full of leaves it can provide shade to keep the pit greenhouse from getting too hot. In the fall, the leaves will fall away making way for the sun.
Another thought when it comes to a wallipini is to build it into a hill since one side of the pit greenhouse is higher than the other. While this does make building the greenhouse easier, there is a cautionary tale to using a hill. If the hill is not very steep or under a lot of gravitation force, it is a good choice. On the other hand, if the hill is steep gravity will become an issue and will cause the walls of the greenhouse to collapse.
While you are constructing your wallipini, you want to make it large enough so that it is practical to build. A pit greenhouse should never be smaller than an 8’ x 12.’ This size is large enough to provide year round vegetables for one person.
Now that you have a basic idea of what a pit greenhouse is, the next step is to build one. Prior to digging deep holes, test out the area with a few test holes. This will test the percolation rate of the soil. To do this test, one will need to fill each hole with water and then time how long it takes for the water to drain away.
If the water drains away in a day or two, the location you have chosen is correct. On the other hand, if the water remains, you may consider picking a new location. The reason being is the fact that a wet soil runs a chance of collapsing and in doing making your pit greenhouse useless.
Once the location has been tested and approved, the next step is to mark out the area. This will first need to be done with a tape measure and stakes. After the area has been marked off, run a string around the stakes. Finish the marking off process by running a line of lime or powdered milk along the string.
Now you are ready for the digging process. You will need to save the first 8 inches of the hole. This soil will be placed back into the hole as topsoil.
As the digging process continues, begin to pack the soil into the sides of the pit greenhouse. This backing will make the strong walls of the greenhouse. As you continue with this process do not forget to make doorways on the each short end of the rectangle. This will be the way that you enter and exit the greenhouse.
Once the walls of the hole have been packed with soil, add a berm on top of long end of the rectangle that faces the sun. This will create the slant by which the top will sit on.
After the walls and berm have been packed tightly with soil, the next step is to prepare the interior. This means a floor will need to be laid. The floor of the pit greenhouse is actually the planting bed and consists of gravel and soil. The first layer of this flooring is a nice thick layer of gravel. This will act as the “drainage” material just like gravel placed in the bottom of a pot. Once the gravel has been laid, one will need to take the “topsoil” that was saved earlier and mix it with compost and appropriate fertilizer that is formulated according to what you plan to grow. This soil layer should be at least 8 inches deep.
The next step in this process is to build the door frames. These are made of simple 2’ x 4’s that have three holes drilled into them. Where these holes are located is very important. You want equal support of these doorways. To provide this, place a hole on the top, middle, and bottom of the door frames. Secure the door frames to the earthen walls by hammering rebar through the holes and into the earth. Prior to attaching the doors, make sure the doorways are plum or level.
Attach the doors to the door frames and test for leaks. You want the doors to fit as snug as possible. You do not want to lose the heat that has been absorbed by the soil. If you have gaps, fill them in with adobe clay, which consists of clay, sand, and straw.
Now it is time to attach the roof but before we move on to this step we will need to check the angle. To get the most out of your pit greenhouse, you will need to have the top of the greenhouse so that it is angled at 39 to 40 degrees. If this is not the case, adjust the design.
If the angle is fine, the next step is to attach all the 4” x 16” poles on 4” centers. Do not worry if there is overhang. You will need this overhang for the plastic sheeting. Once you have the poles placed, secure to the wallipini with rebar as you did the doorways. Fill in any holes or gaps with adobe mud.
Once that is done, run the plastic sheeting over the poles and secure with wooden stripping and nails. Do not worry about the plastic overhanging the end of the pit greenhouse. This will be secured to the greenhouse with adobe mud.
After the plastic has been attached and adobe mud has been added to the ends of the greenhouse, the next step is to seal up any cracks or openings in the structure with adobe mud. Once that is done, you are essentially ready to plant.
While this is a basic plan for a willipini, it is a good guide to get you started on building your own pit greenhouse.