Grow food in a giant cave?
June 3, 2014 10:16 PM   Subscribe

I'm working on a story where some people live in a cave and have to grow their own food inside. I would like some idea of what could realistically be grown in this situation (more details below).

Here's the premise in more detail:

* Ten people live in a giant artificial cave that is a cubic kilometer.
* All of their food must be grown in this cave.
* No natural light.
* They have fresh water flowing in and out.
* They have a nuclear power plant that can power any kind of plumbing, lighting, or machinery.
* The initial materials put into the cave to create farms can be anything, (e.g. soil) but then it is closed off.

I know it's far-fetched, but what kinds of things could you grow? What problems would need to be solved? What would the setup look like?
posted by ErikH2000 to Science & Nature (20 answers total) 7 users marked this as a favorite
 
With fresh water and full-spectrum lighting, it seems like they could grow just about anything hydroponically, although the limiting factor there would be getting nutrients into the plants. Usually this is done via fertilizer, but that just pushes the question out into "how do you manufacture a steady supply of fertilizer". It still seems to me like it should be possible to grow just about anything, but I don't know the mechanics of fertilizer manufacture. Some kind of handwavy "we have a machine that extracts ammonia/potassium salts/whatever else from the compost pile" answer might be enough.
posted by wanderingmind at 10:36 PM on June 3, 2014


Oh! Okay, I actually had to figure this stuff out when I wrote a fantasy-novel variation of this. The most interesting thing I learned is that plants grown in such an environment would likely be limp and droopy, because without wind and airflow to move them around as they grow they end up with really weak stems. So you might need some giant fans to create an artificial breeze.

What I ended up with was a cave with raised beds covering as much floorspace as possible, galleries lined with window boxes up the sides, and espaliered fruit trees around the perimeter.

Other things that would be useful: some kind of composting setup, hopefully involving worms. A wide variety of plants that complement each other in terms of what they put in/take out from the soil. Can you build a fish farm? You should build a fish farm -- maybe net each end of the water supply as it flows through? Or build tanks? Small livestock may be useful: chickens, rabbits, maybe goats for milk. Beehives are an absolute necessity.

Your people would probably end up with a diet that's pretty low in grain-based foods, because grains are a pain in the ass to harvest and process at the kitchen garden scale. Corn would probably be fine, though they'd mostly just eat it off the cob. (You can do the corn/beans/squash triad pretty successfully, I bet.) If the climate control is good enough they could probably eat pretty well year-round.
posted by nonasuch at 10:37 PM on June 3, 2014 [5 favorites]


You might look up some of the Dutch work on closed systems for growing plants.
posted by biffa at 10:43 PM on June 3, 2014


Mushrooms?
posted by Sara C. at 10:48 PM on June 3, 2014 [2 favorites]


It would probably look like indoor grow setups (pot). There's oodles of how-to online for this.

The problems I encounter with an enclosed grow environment (carnivorous plants, not pot):

• Windless conditions can lead to structurally weak/floppy plants, poor air circulation encourages mold/fungus growth which both competes with the plants for nutrients as well as attacks the plants themselves,

• Insect pests and plant diseases spread extremely quickly due to the plants being in close proximity to each other, natural insect control is often not an option as predatory insects and birds aren't able to enter the grow environment, it's surprisingly difficult to eradicate pests in an enclosed space (you'd think it would be otherwise but the pests have no way to escape either so you end up breeding some seriously resilient bugs),

• Plants have evolved in an environment where the source of light is not in a static position. There's some odd growth patterns that happen when the light is straight overhead (lots of top growth, lower growth is shaded by the top and doesn't thrive). There's a lot of maintenance involved with rotating the plants around and appropriate pruning. Related: there needs to be separate heat and light sources, the lights can't be on 24/7 as many plants need a dark rest period to trigger flowering,

• This is less of an issue for plants that catch their own fertilizer like mine do, but good, appropriately nutrient-rich soil is hard to do in closed systems.
posted by jamaro at 10:50 PM on June 3, 2014 [2 favorites]


Do they have fish and downstream soil washed in via the river? That's food and fertilizer coming in steadily.
posted by viggorlijah at 11:52 PM on June 3, 2014


Closed, self-sustaining environments? If it weren't for the cave bit, we could be talking about biosphere 2!

And as for nutrient-rich soil in a closed system, would uh, humanure do the trick?
posted by thug unicorn at 12:10 AM on June 4, 2014


Or, indeed, biosphere 1 (asteroids notwithstanding).
posted by Omission at 1:27 AM on June 4, 2014


Mushrooms and microgreens.

Tilapia (fish) is, I believe, the most efficient protein converter on the planet, but is going to need warm water. Lots and lots of fertilizer for your closed-loop system there.

I wonder if you can mine for inorganic fertilizer.

If water is passing in and out I don't see how the system can be closed, but that makes things easier not harder.
posted by Leon at 1:45 AM on June 4, 2014 [1 favorite]


A real life example from London
posted by Just this guy, y'know at 3:17 AM on June 4, 2014 [2 favorites]


Dunno how you feel about bats in your artificial cave, but they eat bugs and poop guano, which is a highly-effective fertilizer. (But yeah, most closed-ish system food gardens use fish. There's actually lots of info out there for "Preppers" on growing underground gardens in a closed system (i.e., your bunker) for the end of the world. Such as.)
posted by Eyebrows McGee at 5:53 AM on June 4, 2014


I think an issue could be nutrient depletion of the soil. Rotating will help but if this is their sole source of food, there is going to be quite a demand put on the soil. You want to be as eco-friendly as possible in this situation because that's going to make this sustainable.

I'm thinking you want high yield but can be planted closely produce, to make this as efficient as possible. Pole beans, tomatoes, lettuce, herbs, etc.

There is also the issue of fruit. Fruit is harder to grow, so I would focus on berries (not as finicky, won't deplete your soil like fruit trees, easy to preserve, doesn't need to take up tons of space).

Is there a dedicated farmer or team of farmers or do all 10 pitch in? Growing food for 10 with no means of supplementing it is going to be a good amount of work. Someone should be the manager at least. They should be knowledgable about gardening, and especially managing pests and treating diseases.

In an enclosed space, pests or diseases can decimate your crops, so I would consider preserving (canning, or freezing) a certain percentage of your yield even though this is a year round venture.

Root vegetables can take up more space, but in a root cellar they can last for months so I would definitely do that.

A cubic kilometer is big, but not huge and you will be using it for things other than food I assume so think efficiency. Plumbing, lighting, storage, etc all take up space. That is why things that can be trellised like beans and tomatoes are a huge plus. Look up vertical gardening. Also consider the nutrient density of what you grow in a limited space. Cucumbers are tasty and you can have a high yield but you can't really make a meal out of them. Everyone loves the crunch of celery but it doesn't bring much to the table.

You're going to need to do temperature control so be mindful of cool vs warm vs hot plants. Your tomatoes and peppers will want it hot while your lettuce is going to be happiest in somewhat cooler temperatures. So will you grow things seasonally even if they are arbitrary seasons? Will you have some kind of different rooms for plants that need different temperatures to thrive?
posted by Aranquis at 6:53 AM on June 4, 2014 [1 favorite]


The nutrients thing mentioned above would be the biggest thing, I think, so compost is a must...I like the worms idea mentioned above and another possibly viable alternative would be compost tea.
posted by kattyann at 7:23 PM on June 4, 2014


One thing you might need to think carefully about is pollination. You'll need wind and bees at least, you may still need to do some artificial pollination.

Don't throw anything away [especially sewage].

You need the right kind of lighting that produces an energy spectrum useful to plants [i.e. not incandescents]. If this is a long-term setup, you need to think about replacements for failed lighting units. In terms of life expectancy, broad-spectrum LED lighting would be best, but manufacturing replacements requires a pretty high-tech setup.

Note that although you can grow mushrooms, and they taste good, most have next to no nutritional value.
posted by HiroProtagonist at 7:23 PM on June 4, 2014


Wow. I have gotten so many great facts and leads from this. Thank you very much, everyone.

* Pollination by wind, bees, machines
* Wind (fans) for durability of plants
* Plants depending on light position changing/disappearing for them to grow right
* Ideas for fertilizer - bat guano, fish farms, soil/poop nets on water flow, livestock
* Types of high-yield crops
* Temperature control, possibly needing compartmentalizing for different kinds of crops
* Needing a workforce with knowledgable leadership to grow everything
* Real world examples of similar challenges met
* Replacing high-tech parts like LED lights - Ah, jeez, this one will send me on another research quest, actually.

I am thoroughly appreciative.

-Erik
posted by ErikH2000 at 9:57 PM on June 4, 2014


I didn't read the other comments but: Aquaponics! You have two bed/tanks. One has a durable group of fish that grow at a rapid speed (i.e. tilapia). The other has food plants in a hydroponic type setup. The fish water is what you use to water the plants -- it has nutrients and fertilizer. And part of the plants you grow can be fish food. The only input you need is the set-up and the electricity (light). Of course it would work better if you had more fish food, etc., but it still works as a perpetual motion machine.
posted by sockanalia at 11:30 PM on June 4, 2014 [1 favorite]


Have you read the Wool series by Hugh Howey? Post-apocalyptic society living in sealed silos. Not only growing their food but also recycling the air and water. I reckon that (apart from being a great story) it covers a lot of this ground and does it plausibly.
posted by pines at 4:42 PM on June 5, 2014


Replacing high-tech parts like LED lights

Fluorescent lighting might be a happier middle ground. Lifetime & efficiency isn't as good as LEDs, but manufacturing replacements is a lot less challenging.
posted by HiroProtagonist at 7:31 PM on June 5, 2014


On the question of lights, we grow indoor veggies in the winter (and start our summer seedlings) very happily under fluorescents. You can get full-spectrum fluorescents, which are kinda expensive, or use a two-tube fixture and put in one "warm" light fluorescent tube and one "cool" light fluorescent tube, since one gives the red end of the spectrum (stimulates growth) and one gives the blue end (regulates growth, so your plants get lush rather than spindly). We don't use hot grow lights; the ambient heat of our chilly basement (probably around 55 degrees in winter) is enough for lettuces and things like that. (For seedlings that need heat, heat mats under the tray of seeds are cheaper and easier than hot lamps, along with a cheap-o plastic tray cover to keep in some moisture and warm air.)

Anyway, I'm betting inexpensive fluorescent two-tube fixtures (like seriously the cheapest ones on the market ... $19 or something) and the inexpensive, older-style, cool-and-warm tubes would be a lot easier than LED lights to manufacture/maintain in your cave.

We have a set-up kinda like this, but with cheap industrial shelves and cheap industrial fluorescents fixtures each hung by chain from the shelf above. The whole setup -- five shelves, four fluorescent fixtures and all their tubes, a programmable power strip to turn the fixtures on and off at the right time, some hooks and baskets to hang on the sides to hold tools and stuff, and enough potting trays to fill the shelves -- came in at under $250.

"Hothouse" plants that need warmer, wetter weather you'd have to sequester in a climate-controlled "greenhouse" of sorts, but you can manage a whole lot of growing in chilly air with boring old fluorescents.
posted by Eyebrows McGee at 9:08 PM on June 5, 2014


In regards to space, since you are using artificial light, you may be able to stack your growing trays upward. Look at the picture in that London tunnel that Just this Guy posted. They have their plants on 3 foot tables. Why? You could put another row of plants on the ground and suspend more lights from the bottom of the tables. You could build shelves over the tables and have another level. If you were to build a rotating set of shelves like a rotisserie chicken oven or a jewelers display case, you might be able to use that to prevent the idea of the straight-overhead light source that jamaro mentioned.
posted by CathyG at 4:14 PM on June 6, 2014


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