Step 1: Size and Placement
An underground greenhouse uses the heat trapped in the ground to your advantage and maximizes the sun's rays when they are available, according to the Benson Agricultural and Food Institute.
You'll dig a rectangular hole in the ground, anywhere between 6 to 8 feet deep, which will then be covered with plastic sheeting to allow the sun to pass through. You can make your greenhouse as large as you would like, but be sure that the longest side faces the sun, so your plants get ample light to grow.
Digging this deep into the ground will require heavy equipment designed to handle larger tasks. A backhoe will be needed to dig a hole deep enough for the greenhouse. If concrete needs to be removed, you can rent a compact or electric hammer. If concrete needs to be added for the foundation, a concrete mixer or buggy can be utilized. All of these items can be rented from a company like Neffrental or borrowed from friends. Once you have completed the first step in your greenhouse, you will then need to construct the roof.
Step 2: Roof Installation
Insulating against the cold will help trap and retain heat during the winter months. Your greenhouse roof should be made of a double layer of plastic sheeting placed on top of your hole and affixed tightly around the perimeter of your greenhouse. This sheeting will help to keep heat within the greenhouse when it is dark and will also protect from excessive moisture, which can rot your plants. Essentially, the roof allows you to contain heat within a smaller area, and it is then able to help keep a moderated temperature, necessary for the stability required for plant growth.
Step 3: Maintenance
Another critical component to making sure your greenhouse flourishes is appropriate ventilation, so things do not get too hot and humid. This system needs to be considered as you are constructing your greenhouse, so you can appropriately control the temperature in your greenhouse year round. According to the Royal Horticultural Society, maximum-minimum thermometers help gauge how things are running in your greenhouse, and automatic vent openers help moderate conditions throughout the day as needed. During the winter months, overheating will likely not be an issue, but in the summer months tools like maximum-minimum thermometers can help you determine how much shade your greenhouse needs to maintain optimal efficiency.
Constructing an underground greenhouse is an excellent sustainable way to keep fresh vegetables coming year round, and with just a little bit of planning, you can build your own thriving horticultural bliss. It's part of a great food solution for the prepared survivalist.