In truth, this post should read ‘Growing crops in artificial environments’, because it applies equally to crops grown in a hypothetical space station as it does to crops grown on the Moon, or Mars or any fictional celestial body.
I’ll start off with a few open doors:
– All crops we grow as food today exist in some form in the wild. In all of those cases, humanity has bred better varieties to the point where the original plant bears no more than a passing resemblance to the crop variety. For example, compare a wild rose with the ones you buy at the florist. It’s hard to believe the commercial rose is directly descended from the wild rose. This has come about by selecting varieties with desirable characteristics (in other words: mutations) and propagating them, selecting the best plants out of that crop, and so on, and so forth. While the selection process is human-driven, there is nothing unnatural about the commercial rose’s DNA.
– All plant species evolved to be suited to their native climate. The banana is a tropical crop and will do poorly when temperatures are too low. Similarly, the banana evolved to grow in a climate where the temperature range is fairly narrow (in other words: where it’s always hot), and where the daylength doesn’t vary much either. Never thought about this? Well, here’s an everyday illustration: I live in Sydney (33 degrees south). I go to the gym at 6.30 most mornings. At that time, the TV in the gym has the news on. It’s summer right now, and at 6.30 it’s pretty light in Sydney. If, however, the news program crosses to someone in Cairns (16 degrees south), you’ll see that it’s still pitch dark over there. If they cross to someone in Hobart (42 degrees south), it has been light down there for ages. These three cities are more or less on the same latitude. In winter, exactly the opposite will happen. It will be light in Cairns, dusk in Sydney, and still pitch dark in Hobart.
To sum up, Cairns has much less annual variation in the length of its day. This is, incidentally, why daylight saving in the tropics is neither sensible nor desirable. Trust me, I lived there. You do not want daylight saving. (/soapbox).
What does this have to do with crops?
Well, you’ll probably have noticed that most crops are highly seasonal. People in our cities don’t notice this so much, because food suppliers use two mechanisms to extend availability: 1. storage (if you buy apples in February, I can guarantee that they’re about year old), 2. different source areas (with its handy dual temperate/tropical climate, Australia can grow temperate crops in winter in the tropics and in summer in the temperate regions. Surprise, surprise, most of our staple vegetables are temperate crops).
But the tropical crops that are highly seasonal (fruit trees—the banana is NOT a tree) are only available in summer. This is why mangoes come onto the market in November and tail off in January.
(for the record: Australia imports almost none of its essential fresh food)
OK, seasonal crops. Bowen mangoes flower in late August, and the fruit is ripe in the first week of November.
Why does the mango tree flower in August? Because, as in animals, plant reproduction is a hormonally-induced process that responds to triggers.
These triggers are:
– Temperature. Many plants need a cold period to flower. If you’re sick of your Phalaenopsis orchids always flowering in May, put them in a cool room at 15C for two weeks, and they’ll flower any time of the year.
– A dormant period. This is especially important in temperate plants. Dormancy is often controlled by temperature, but only because temperature triggers the production of certain plant hormones. Are you a Sydneysider who has lived in Europe? Have you ever noticed how the paltry few European oak trees in Sydney hardly lose their leaves in winter, much less produce acorns? This is why. No loss of leaves = no dormant period = no acorns.
– The real biggie: daylength. Almost all plants will react to changes in daylength by speeding up their maturity, or delaying it. This is what you are doing trying to grow a crop outside its native climate zone. Parsley, a temperate herb, is a natural biannual, but when you grow parsley in the tropics, it will neither flower nor die after two years. Parsley needs a short day (in other words: a temperate winter) to induce flowering.
And now you’re taking this hotchpotch of plants with their varying requirements into space and growing them in a controlled environment. Each species has its own maturity triggers and sensitivities. Some plants (tomatoes) are pretty much insensitive to anything you throw at them. Others (wheat, maize, rice) can be far more fussy. And daylength rhythms can be disturbed by something the strength of a street light at night (ever noticed how oak tree branches surrounding a street light are weeks ahead of the rest of the tree?)
If you want anything approaching the full range of crops you can buy in a regular supermarket, you’d have to make some adaptations to your artificial environment design. You could modify the artificial environment but supplying a few chambers with different conditions, or you could breed plants that are less sensitive to daylength (this sensitivity is controlled by a single gene). In any case, taking everyday Earth crops into space for mass food production will require a lot of thought. That, or your characters will get mightily sick of eating tomatoes.
