In a quest to find a practical way to grow food year-round, one could find many different variations of ways that people are accomplishing just that. Not long ago, I came across a greenhouse idea on social media that seems to be gaining popularity, called a walipini.
What is a walipini greenhouse? A walipini (or underground) green house is a greenhouse that is dug into the ground, typically well below the frost line, which uses a combination of heat from the sun and naturally occurring geothermal heat to keep plant life warm.
Walipini greenhouses were invented in the 1990’s by philanthropists volunteering in Bolivia. The name in the local language means “place of warmth”. They constructed these by digging pits in the ground, and covering them with simply framed roofs with a plastic sheet covering. This made the structures cheap to build, while still providing and energy efficient space for year round growing in stable temperatures.
Walipini Construction
It seems simple enough, right? Dig a hole in the ground, throw a plastic sheet over it and… wah-lah! Walipini! Well, maybe it’s not exactly that simple.
The design starts by digging out a trench, and while that maybe simple, but backbreaking work, there are a few other things to the design. Your pit will need to be about 8 feet deep, with a ramp going into it. You can also dig stairs, but there maybe an advantage to being able to roll a cart or wheel barrow in and out.
You will need the floor to be slightly slopped from the center to the edges; this will help with water drainage. As an extra precaution, you can also dig open gravel wells in the corners, to store access water.
Something else you should be mindful of when creating your walipini are the earthen walls. The original designers simply rammed the earth to solidify the walls of the structure, but this may not work with the soil type in your area.
Some people construct walls underground to keep the earth from eroding inwards. Cinder blocks can be used for this, or even concrete or wood plank walls. This just helps to ensure that your structure helps hold up to the tests of time.
Another solution to this problem, or when building wall supports is cost preventative, is to angle the earthen walls outward.
After you have your space carved out, a few layers of gravel is laid down across the ground. Start with larger gravel, then layer to smaller gravel. This helps to drain off excess water.
On top of the gravel, you will be adding topsoil, or planting soil. Deeper layers of soil, or subsoil, are not as nutrient rich as topsoil, so re-adding a layer of topsoil makes for a more nutrient rich environment for plants to grow than just planting in the subsoil.
Once the inside of the walipini is prepped and ready, its time to start thinking about the roof. The greenhouse needs a roof that is pitched, and facing towards the equator for optimal sunlight.
The original designs used the earth from the digging to build up the elevation on one side of the pit. This mound of dirt, often referred to as a berm, is used to build the top slant of the roof. Of course, you can always build this out of stone or lumber, but remember this was meant to be a cheap project initially.
The roofing was originally built of bamboo, or tree branches that were available on site. They needed to be resourceful if they were going to build many of these structures as possible to help poor farmers in Bolivia.
The tree branch framed roof was then covered with two layers of plastic sheeting, one on the inside, and one on the outside. If you have done any other reading on greenhouses, you may know why that is, but just in case you haven’t, having two layers separated by air makes for excellent insulation rather than one layer alone.
Many people choose to build lumber frames in their designs, and some even use PVC pipe. You can use whatever suits your budget the best.
You’ll want to make sure the roof extends past the pit by at least a foot. This will help keep rain runoff out of the greenhouse. You can also use a gutter system, or a ditch, to run rainwater away for the pit. This just helps keep the pit from flooding in a heavy rainfall.
Venting is something that can be included in the roof build. You can install a panel in the roof that opens to vent during warm weather, or install fans on either side.
This type of greenhouse design was intended for a location that is close to the equator, and gets plenty of light even in the winter. Places in higher latitudes of the world get half as much, or less, light in the winter. This means that the sun stays very low on the horizon, and if all your plants are below the surface of the ground, guess what that means? You got it, you’re plants are not getting any light! The lack of sun also means your plants are not getting as much warmth, and your greenhouse isn’t being properly optimized.
You can get around this however, by building a walipini that’s only partially underground. This altered walipini could be dug only halfway in the ground with the top half being a more traditional green house structure.
Another option if you have a southern facing hill on your property is to build your walipini into the hill. This gives you some of the same benefits, but you still get all the light you need.
The last step in the build is to install a good door, at the base of the entrance ramp. You can do this using 2×4 lumber. By drilling holes in the lumber, you can secure the frame to the earth by driving stakes or rebar through the holes. If you’ve built a lumber roof, you can also attach the top of the door frame to the roof framing.
Remember to fill in any gapes between the door frame and the earth. It will need to have a good seal to hold maximum heat.
Pros and Cons of Walipini Greenhouses
Is a walipini construction right for you? Lets look at some of the benefits and downfalls of this type of building
- Pros
- Uses geothermal heat to keep plants warm in winter
- Geothermal cooling in the summer to keep plants from over heating
- Can be constructed cheaply
- Can be more visually appealing than an above ground build
- May require less maintenance than other options, with only a roof to repair
- Soil better maintains moisture
- Less weeds
- Can double as a structure to keep livestock warm
- Cons
- May not get optimal sun in your area
- May require additional construction to reinforce the earthen walls
- People or animals could fall through the roof
- Plastic sheeting roofs could collapse under ice and snow
- Maybe more difficult to water than other choices
- Could potentially flood in heavy rains
Related Questions
What can you grow in a walipini? Anything that grows in other greenhouses will also grow in a walipini.
How much does it cost to build a walipini? The cost of building a walipini varies depending on what features you want to use, but some say that it can be built for under $300.
Do you need additional heat in a walipini? Generally speaking, you should not need extra heat in a walipini, however it could still be added for to boost production.
