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How to Build an Underground Greenhouse: A Complete Guide

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According to the CDC, only 9% of American adults eat enough vegetables. So, the odds are that you’re not eating enough. You can help increase your veggie intake by growing some at home. 

Understanding how to build an underground greenhouse is essential for preppers because it provides year-round vegetables and herbs.

Growing your own food isn’t difficult in the summer, but winter gardening is a lot more complicated. It is made infinitely easier when you have a space that is insulated from the elements.

Building an underground greenhouse may seem daunting, but many people took existing structures and simply renovated them to suit their needs. What you need are some examples and directions. 

How Does an Underground Greenhouse Work?

underground greenhouse

Underground greenhouses work similarly to standard above-ground ones. A layer of plastic or glass allows warm sunlight in, trapping it and heating the greenhouse.

However, geothermal heat also plays an essential role in underground greenhouses. The earth holds onto more of the trapped heat and releases more into the greenhouse space slowly, keeping it warm. It’s an excellent insulator.

Underground greenhouses also hold more humidity, which can be great for some plants. You will need more moisture regulation to ensure it doesn’t become too humid for the food you want to grow.

Overall, underground greenhouses are very energy-efficient because they trap heat and are well-insulated by the earth. You won’t need to heat them yourself if you build them correctly.

Building an Underground Greenhouse

This DIY project can be rewarding for preppers since you’ll have an extended growing season for emergency food

Before starting, you should do ample research. Make sure you check the soil conditions and climate where you live. You might also need a permit to start digging and building the greenhouse.

Tools and Supplies

digging land for greenhouse

You don’t need many supplies to start building your underground greenhouse. Many preppers already have the materials at home, especially those interested in gardening.

You can also improvise by replacing some of these materials with what you have. For example, if you don’t have bricks or concrete blocks, you can use tires filled with earth. Many people also upcycle used windows by swapping them with plastic sheets.

You will need:

  • Shovels and other digging tools
  • Greenhouse covering (polyfilm plastic)
  • Wood planks or PVC pipes for the roof
  • Gravel for the flooring
  • An exhaust fan
  • Bricks, concrete blocks, or stones
  • Earthbags or straw bales

Underground Greenhouse Directions

Building the greenhouse is straightforward:

  1. Dig out the foundation: Use your shovel to excavate six to eight feet in the ground in a rectangular shape. Make a slight slant towards the greenhouse’s entrance for drainage.
  2. Lay down your foundation material: Spread a layer of gravel on the floor of your greenhouse.
  3. Line the walls: Form walls inside the greenhouse using bricks, concrete blocks, or stones. 
  4. Add more insulation: Line the walls with earthbags, straw bales, or other materials.
  5. Build the roofing support: Set up poles using your roofing material in the middle of the greenhouse. You can secure the vertical beams in the ground or place them in concrete barrels.
  6. Connect the beams: Connect the poles to the horizontal beams, spacing them evenly.
  7. Install the roof: Spread and secure the plastic sheet over the beams.
  8. Add ventilation: A fan and leaving the door open are usually enough for a small greenhouse.

Things To Consider Before Building

cute underground greenhouse

There’s a lot to consider before you start building the underground greenhouse. They’re more complex than standard greenhouses, so you’ll have more small details to keep in mind.

Take all of these considerations and use them to plan out your design:

Site Location and Size

You must dig in an area with good drainage and plenty of sunlight. Measure and mark the area you want to excavate on the ground first.

You also want the greenhouse to catch as much sunlight as possible. Think about where the sun lands most during the day.

So, for those in America, you want the greenhouse to have a southern wall lower than the northern one. The further north you are, the more angled you need the roof to be for it to capture as much sunlight as possible.

Finally, you don’t want to dig into the water table. Underground water can be just below the surface or very deep in the earth, depending on where you live.

Call 811

You don’t want to dig into any utility lines.

So, call 811 before you dig if you’re in the States. The person on the other end will walk you through the process of following the digging guidelines for your location.

Proper Ventilation

Underground greenhouses need more ventilation. You can trap too much heat and humidity otherwise. Plus, you need airflow.

Exhaust systems, like fans and vents, are a great option. However, you can also use natural ventilation, like windows.


Your greenhouse will need maintenance from time to time. You will need to add more gravel to the flooring, replace the roof, or add more ventilation.

Think of your greenhouse as an ongoing project. There’s always something to replace or make better.

You’ll also need to monitor the internal conditions of the plants. You may need to adjust the humidity levels or temperature to make them more suitable for your produce, depending on the season.

Add Other Features

Lastly, think about whether you want more features in your greenhouse. You can add heating or irrigation.

A popular option is solar lighting for when it starts getting dark outside early.

Many preppers also build wooden planters or fill the greenhouse with grow bags.

What to Grow

growing vegetables in underground greenhouse

You can grow all sorts of food in your underground greenhouse. Plants that are a little more hardy are going to go a long way.

These will last through extreme cold and given the protection of the greenhouse they will thrive. The temperatures underground do not fluctuate as much as they do above ground.

That is why these are some of the more successful greenhouses that the average person can build in their back yard.

Would a Normal Greenhouse Suit You More?

You should consider if an above-ground greenhouse would benefit you more. Customary greenhouses are usually easier to build and more cost-efficient.

You’ll want to research your options. Here are a few ideas to consider to help you decide:


To summarize, you can build an underground greenhouse at home.

You’ll have plenty of produce for canning, allowing you to make a supply. Many people also love having access to fresh produce year-round.

If SHTF, you won’t have to worry about having vegetables, and you’ll have a more sustainable lifestyle overall.

How to Build an Underground Greenhouse: A Complete Guide