Life Support Systems
Light Is the Throttle
What a mine in Idaho and a garden in Alaska taught us about growing things fast — and what continuous daylight does to a plant that never gets to sleep
There is a habit of thinking about plants as slow. Six years for a sapling to become a tree you could lean a ladder against. A whole summer for a garden. From our research and from what we have seen with our own hands, the slowness is not in the plant. It is in the light.
The nursery under the mountain
I grew up in Kellogg, Idaho, in the shadow of the Bunker Hill Mine. By the 1970s the hills around Kellogg were bare — decades of smelter emissions had killed everything, and the soil was corrosive enough that anything that sprouted died. In 1972 the company hired its first forester, a young Army veteran named Ed Pommerening, and an executive told him he was going to make the hillsides green again.1
The Forest Service told him he would be lucky to get ten percent survival in that soil.2 What he did instead is the part that matters to anyone thinking about growing food on the Moon. In August 1975, company carpenters built him a forty-foot greenhouse three thousand feet down inside the mine.3 Underground, on lights, he raised the seedlings that high school and college students planted on the slopes every spring — two hundred trees a day per planter — and over twenty years he and those kids put seven thousand acres of pine, fir and larch back on the mountains.14 The mine that had stripped the forest for timber became the incubator for five million seedlings.5
Here is the part we cannot yet source. Growing up there, the story we heard was that a sapling in that mine put on in six months what it took six years to grow on the surface, because the light never went off and the temperature never moved. We have not found that figure written down anywhere. We are still looking, and if you worked at Bunker Hill, or know Ed’s records, we would like to hear from you. What we can say is that the nursery was real, it was underground, it ran on artificial light, and it produced enough trees to reforest a valley.
An inch a day
I live in Alaska now, where in June the sun barely sets. Planting there, I have measured an inch of new growth in twenty-four hours — not over a week, over a day. Anyone who has gardened in the far north knows the cabbages. Alaska grows cabbages that weigh more than a small child, and the reason is not the soil or the seed. It is twenty hours of daylight, every day, for weeks.
Put those two observations side by side. A plant given more light grows more. That sounds obvious, but it inverts the way most people plan a greenhouse. Light is not a condition the plant lives in. Light is the throttle. Push it and the plant runs faster.
For a habitat that is the best news in the whole life support problem, because light is the one input we control completely. Off Earth there is no weather, no cloud cover, no winter, no night unless we make one. The sun in space is constant, and in a sealed habitat every photon that reaches a leaf is one we chose to put there. If yield follows light, then yield is an engineering decision.
What the plant does at night
But it is not that simple, and the research is clear on why.
Greenhouse growers have been trying for decades to run tomatoes on twenty-four-hour light, because if you can keep the lights on all day at a lower intensity you need a third fewer lamps to deliver the same total daily light.6 It mostly does not work. Most modern tomato varieties, along with eggplant, potato, peanut and others, develop leaf injury under continuous light — the leaves yellow between the veins, photosynthesis drops, and yield falls.6 The leading explanation is that the plant’s internal clock gets scrambled; genes that manage light capture are timed to a day-night rhythm, and when the rhythm never turns over, the machinery runs out of balance and the leaf damages itself.7
The plant needs a night. Not for rest in the way we rest, but because its chemistry is built around a cycle, and it uses the dark to finish what the light started.
The encouraging part is what growers have found recently. If the light changes — dims at “night,” shifts to blue, drops the temperature by ten degrees — the injury largely disappears even though the lamps never fully go off.78 Give the plant a signal that it is evening, and it will accept a day with no real darkness in it. Variation, not darkness, is what it is asking for. Some wild relatives of the tomato tolerate continuous light outright and yield more under it, and that trait has been bred into commercial lines.9
So the throttle has a governor on it. Push light up and growth follows, until the plant loses track of time and starts to fail. Give it a rhythm — day, evening, a cooler stretch, a warmer one — and you can push much harder.
That echoes something we wrote about in the worms-and-bees article and intend to come back to: living things do not want steady conditions. They want variation they can set their clocks by.
Fast wood is weak wood
There is a second governor, and it is one that anyone who has handled lumber already knows. Fast-grown wood is weak wood. Wide growth rings mean less dense fiber, and a tree that has never had to stand up to a wind never builds the reaction wood that lets it stand up to one. At Biosphere 2, under glass with ducted air and no wind, the trees grew fast and thin and some of them fell.10
We have not seen anyone tie the underground-nursery growth rates to timber quality, and it may not matter for a seedling that gets planted out on a windy hillside at eight inches tall. But it matters for a habitat. If we are growing trees for structure — and some of the habitat proposals we follow do count on it — then a tree grown fast under perfect light in still air is not the tree we want. It is a tomato that never had a night.
Where this leaves us
From what we have found, three things hold together:
Light drives growth harder than most people expect, and in a habitat light is the one thing we control completely. That makes food yield an engineering decision to a degree it has never been on Earth.
Plants need a rhythm, not just photons. Continuous light without variation damages most crops. The fix is not darkness — it is a day that changes.
Fast growth costs something. For a lettuce, nothing we care about. For a tree, strength. Whatever we grow for structure will need wind, or a stand-in for wind, and time.
We got here through a story from a mining town, an inch of growth measured in a garden, and a literature that is mostly about tomatoes. If you have grown under lights in a mine, a submarine, a research station, or an Alaskan summer, we want to hear what you saw.
Come join us. Because we are Star Bound.
John LangEditor
Ideas in Star Bound are published open — take them, build them better. Our open proposal.
A note on where this comes from. I am not a metallurgist, a spacecraft engineer, or a degreed engineer of any kind. But I am a practical one, with more than forty years in heavy industrial construction: welding, millwright work, hydraulics, mining, and thirty-three years of electrical construction and commissioning on the North Slope of Alaska, in a place that punishes anything built wrong. Much of that time I have worked as a field engineer, which means I am the one standing in front of the equipment when the drawing turns out to be wrong, and the fix has to be made on the spot, with what is on hand, and has to work the first time. Anyone who has done that long enough learns that a lot of engineering gets corrected in the field by people with more experience than the people who drew it. That is the eye I bring to these subjects: not what should work on paper, but what actually gets built, and what breaks. The facts I take from other people are footnoted so you can check them and read further. The ideas built on top of those facts are my own, and I would rather see them knocked down by somebody who knows better than left standing because nobody looked.
Sources
- Spokesman-Review, “Forester’s commitment revived Bunker Hill landscape” (July 6, 2010) — https://www.spokesman.com/stories/2010/jul/06/back-to-nature/ ↩
- Carlson Strategic Communications, “The Underground Trees: How the Coeur d’Alene Mountains Were Reforested” — https://carlsonstratcomm.com/the-underground-trees-how-the-coeur-dalene-mountains-were-reforested/ ↩
- Wildfire Today, “Why Idaho’s Silver Valley is forested again” — https://wildfiretoday.com/why-idahos-silver-valley-is-forested-again/ ↩
- Shoshone News-Press, “He spoke for the trees” (April 28, 2023) — https://shoshonenewspress.com/news/2023/apr/28/ed-pommerening-man-who-didnt-give/ ↩
- Coeur d’Alene Press, “Huckleberries” (January 8, 2023) — https://cdapress.com/news/2023/jan/08/huckleberries/ ↩
- Lanoue J. et al. (2024). “Tomato and mini-cucumber tolerance to photoperiodic injury involves photorespiration and the engagement of nighttime cyclic electron flow from dynamic LEDs.” Frontiers in Plant Science 15:1384518 — https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2024.1384518/full ↩
- “Dynamic lighting mitigates photoperiodic injury in greenhouse tomatoes.” PMC — https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12913140/ ↩
- Haque M. S. et al. (2017). “Temperature Variation under Continuous Light Restores Tomato Leaf Photosynthesis and Maintains the Diurnal Pattern in Stomatal Conductance.” Frontiers in Plant Science 8:1602 — https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2017.01602/full ↩
- U.S. Patent 9,907,240, “Tomato plants exhibiting tolerance to continuous light” — https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/9907240 ↩
- Wikipedia, “Biosphere 2” — https://en.wikipedia.org/wiki/Biosphere_2 ↩
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