How much food can you grow in a bunker?

In 2023, the global bunker-building industry was valued at just over 23 billion USD; by 2030 it’s expected to be over 36 Billion. This rise in bunker building is mostly due to the world elite, who are becoming increasingly paranoid about the threats they may face and have invested in personal survival spaces to hide away from any dangers that come their way.

One of the biggest flaws in these luxury bunkers is the length of time they intend to stay down there, with the average luxury sub-terranean dwelling often not stocked with more than a month’s worth of food and power. Even if a bunker were stocked with enough supplies to last for years, the problems that come with a nutrient deficiency from eating survival foods for so long will take their toll, and sooner or later something fresh will need to be eaten.

This means producing fresh food underground, but unfortunately, there are 3 main restrictions when it comes to growing food in a bunker, which is power, space, and lighting. It should be noted that the majority of bunkers will be connected to the main power grid, and even if they do have their own means of producing power, it will likely only last for a few weeks at the most.

What do you need to grow food underground?

There are many factors to growing food in a bunker such as space, power, air quality, growing medium, water, and nutrients. For the following information, we shall consider that electricity isn’t a problem, and also the air coming in from outside isn’t contaminated in a way that would affect the plant’s growth, leaving just space, lighting, and growing medium as considerations.

Lighting options

When it comes to artificial growing lights there are 3 choices. Fluorescent lighting, H.I.D bulbs, and L.E.Ds.

LEDs (light-emitting diodes)

Coverage – 4sq feet per light, with 300 watts minimum needed for a full plant cycle.

These are the best type of artificial growing lights on the market and offer the full UV spectrum of light, but also have concentrated colors to boost certain aspects of the plant’s growth cycle. These often appear with a purple light from the combination of the blue and red bulbs within the light board and provide a much more powerful and concentrated light for optimum plant growth. Even though they are the best lights for indoor growing, they also have the least amount of coverage and also cost the most. This is only an option if power and money isn’t going to be a problem.

Florescent bulbs

Coverage – 6sq feet per 200 watts, only suitable for salad greens and nonfruiting or root crops.

These provide a full spectrum of UV light but in a relatively weak form. These are a good option for growing a single planter of something fast-growing, but the light power becomes too weak to properly put vegetable crops through their full cycle. A good choice for smaller salads and fast-growing leafy crops, but any kind of fruiting plant or root vegetable will turn out poorly.

H.I.D bulbs (High-intensity dispersion)

Coverage – 10sq feet per 600 watts

These lights give off a full spectrum like the others, but cover a much larger area and offer more light power to put the larger crops through their full growing cycle. The main problem with these is that they create a huge amount of heat, and if you’ve ever touched one of the old 60w lightbulbs when it’s on, you can imagine how hot a 600w bulb would get.

(Both Aquaponics and Hydroponics don’t require soil, reducing the need for supplies and the risk of pests)

Growing medium options

There are two practical choices when it comes to growing your plants: compost or hydroponics.

Compost is the easiest and cheapest choice, but it will cause more problems in the confined and humid conditions of the grow room. It’s the most likely to produce mold and will take more water for a full growth cycle than hydroponics. There is also the problem of space, with a stack of compost bags taking up as much room as a large planter. Growing root vegetables also requires substantially more compost than salad crops and has to be spaced further apart, which means a larger physical space with fewer crops.

Hydroponics is a method of growing without soil, and the plants sit in small cups with their roots hanging down into a pot of water. This water is filled with nutrients that are cycled around the system where the water quality can be easily monitored and adjusted accordingly. The main body of the plant stays above water, as do a portion of the roots which ensures the plants don’t drown, and have maximum access to the air. The main problem with this growing method is the roots are permanently submerged, which means that any kind of root vegetable is out of the question.

What kind of food can you grow in a bunker?

Soil options

Radishes, spring onions, shallots, carrots, beets, fennel, celery, cress, dwarf beans, dwarf peas, or any kind of shallow root crop that takes a maximum of 60 days for a full cycle. Any kind of large and deep root crop like potatoes will take up too much space and growing time. The same problem comes with grain, as most grain crops take around 100 days for a full cycle and won’t provide close to the same food weight as a faster-growing smaller crop.

Hydroponic options

Lettuce, spinach, mustard greens, kale, tomatoes, cucumbers, strawberries, swiss chard, watercress, peppers, bok choy, or any kind of long-rooted plant where the main body can stay above water with only the roots hanging down. Any kind of root vegetable is not an option with this growing method as the constant contact with water will cause them to rot.

So how much food can you grow in a bunker?

This will depend entirely on space and the resources you have available, but here are a few examples of what would be possible to produce in a bunker grow space.

The shelf setup – 1 meter by 5 meters squared

example 1 – L.E.D lights growing spinach in soil

A minimum of 200w of power per light, with one light per meter, provides enough light power (measured in a unit called lumens) to put the plants through their full growth cycle.

Power required – 1kw per hour, 16 hours of growing time per day equals 16kw per day. for a 45-day fast crop, this equals 720kw of power.

Output – In spinach, you could cram around 40 plants in a 1-meter square which you would be able to harvest twice in a 45-day period. Due to the leaves being smaller for the first harvest, you could expect a total of around 1.25 kg of edible produce per square meter, for an estimated total of 6.25 kg after 45 days. Enough to feed one person for 2 days.

example 2 – L.E.D lights growing spinach in hydroponics

The same light power of 200w per light per square meter would be needed, but now with the addition of a hydroponic system requiring a constant average of 50w to operate the pump.

power required – the same requirement of 720w for a 45-day grow plus 1.2kw per day for the hydroponics system which is an additional 54kw of power.

Output – Crops in hydroponic systems with the right nutrients can produce around 50% more produce for the same amount of crops. You can also double the number of crops in the same space as the roots aren’t competing for root space like they are in soil. The 6.25kg produced from soil could be as high as 9.75kg from the same amount of plants, but with twice the number of plants in the same space, this could be as high as 19.5kg, though this is the best-case scenario with perfect growing conditions and nutrients.

Alternatives

Using high-intensity dispersion bulbs would require at least 2 to cover the grow space, and would need to be around 500w per bulb. These can be placed further away for more coverage, but the light power is reduced so much from the extra distance away from the plants that they don’t benefit from the extra power. The other problem would be the large amount of heat they produce, and placing them in a confined bunker room with give it an almost tropical climate.

The grow room set up – 3 meters by 6 meters

Example 1 – L.E.DS in soil growing half vine crops and half leaf crops.

Power required – The larger the grow space available, the more it’s worth swapping over to H.I.D bulbs. If you need 1 L.E.D light per square meter of at least 200w of power, this would require 18 lights. A 16-hour grow day would require 57.6kw of electricity per day, that’s 2.59 megawatts for a 45-day grow which is a ridiculous amount of power.

Output – Spinach would be the fastest and most productive leaf crop, and would yield about 2.5kg per square meter, for a total of 22.5kg. As for the vine crops, according to Research Gate, the average yield for tomatoes is 18kg per square meter over a 100-day grow with multiple harvests. This gives you 162kg after 100 days, but this will more than double to amount of time the lights are on and also double the amount of power they require, which would mean over 5 megawatts of electricity for a single grow cycle, something that wouldn’t be possible without being hooked up to the mains.

Example 2 – H.I.DS in soil growing half vine crops and half leaf crops.

Power required – A single H.I.D light would be able to cover a grow space of 3 meters sq but would have to be of a higher power in order to give around 200w of lumen energy when the light hits the plants. To get more coverage they can be placed further away but would require more energy to provide the same growth power, and at this distance, you would need at least 700 watts of electricity going into each light to cover the whole grow space. 1.4kw an hour for 16 hours is 22.4kw a day, giving a total of 1008kw for a 45-day growth.

Output – The total produce from growing under this kind of lighting can be expected to be around 25% less than under L.E.D.s. The reason for this is even though they contain a full spectrum of UV light, they don’t have certain colors concentrated within the light to boost aspects of their growth as L.E.Ds do with their blue and red concentrates.

Yield increase from hydroponics.

Anything that can be grown in a hydroponic set-up can grow up to 50% faster or 50% bigger, depending on what it is and its conditions, but this is only in the best-case scenario. The additional power required would depend on whether you’re using individual pots or tubes, with the second option being much more power efficient. You would need about 50 watts of power to run around 10 individual grow pots, which would hold 10 plants, or the same amount of power to run the water through tubes holding several times the number of plants.

A real world example

The world’s first underground farm
Located 30 meters underground beneath Clapham High Street is an old World War 2 air raid shelter that was turned into a massive underground farm called “Growing Underground”. The farm uses hydroponic technology and claims to use 70% less water than conventional farming while producing around 6 times the amount of food for the same growing space in soil. The only thing the farm doesn’t state is how much electricity they use, with the pictures of “Growing Underground” showing row after row of L.E.D lighting.

The company claims to have increased the growth speed of the crops by a minimum of 7%, with some crops growing up to 50% faster, and the average yield being 24% higher. Unfortunately, Growing Underground was a private company and they seem to have dissolved in November of 2023. The reason behind this comes down to funding, as salad isn’t the most profitable crop to pay for central London real estate, a tremendous amount of electricity, and technicians trained in advanced hydroponic growing techniques. While the costs of living remain what they are, it seems the chances of a successful underground farm opening again are very small.