Deever, D. , Assistant Professor, Extension Educator, Lincoln County, University of Nevada, Reno

ABSTRACT

Mars is a six-month journey each way, which means that any large number of space pioneers who venture there and plan to stay for an extended period of time will need to begin subsistence farming shortly upon arrival. The crop seeds they bring must be capable of withstanding extreme environments; have superior storage ability; produce palatable and nutritious products that offer enough variety in greens, grains and popular flavors to satisfy palates; offer a wide range of other useful attributes when it comes to fiber, fuel, construction materials, industrial chemicals and medicines; and possess the ability to germinate and grow quickly with less water and less need for soil amendments than the vast majority of modern crops. The purpose of this study was to catalog those plants known as “superweeds” that hold a remarkably high potential of usefulness for future off-world space colonists, since the same qualities that make superweeds a threat on Earth, qualifies them as being potentially the most reliable crops for space settlers during the early years of colonization. Moreover, this study was accomplished in large part to create an instrument to assist space settlement planners in understanding vital criteria for selecting the most beneficial crops, whether superweeds or not, which offer the highest potential usefulness and assurance of harvest success. When it comes to the need for this information, time is of the essence, since plans are currently underway to begin colonizing Mars as soon as 2026. The vast amount of data collected for this study will eventually become the contents of a scholarly book titled, Space Pioneers’ Crop Book: A Guide to Selecting, Cultivating and Processing the World’s Most Reliable Crops for Earth-independence on the Moon and Mars.

INTRODUCTION

Futuristic plans to colonize Mars are presently underway and moving full-steam ahead (Zubrin, 2014), optimistically slated to begin as soon as 2026, when the first 80,000 space pioneers will begin contributing $500,000 each for their journey to what is literally the new world. The grand vision of Elon Musk, CEO and founder of Space X, and the major force who is spearheading this effort, has as his goal to eventually place one million pioneers on the Red Planet (Vance, 2015). Elon Musk firmly believes that his plan is essential for the survival of the Homo sapien species, since having all humans live only on one planet makes them vulnerable to a wide variety of potential extinction-level events. Such a bold endeavor to propagate the species outward from Earth, requires much planning and many new innovations, not only in technology, but equally in the field of agriculture, especially concerning the types of crops that should be initially grown to supply the needs of a million people (Brown, et al., 2008).

To meet that quickly approaching need, it is the premise of this study that the category of crops with the greatest potential to supply enough of the food, fiber, construction materials, industrial chemicals, fuel, and medicinal needs (Stepp & Moerman, 2001; Stepp, 2004; Duke, 2019) of our space pioneers might best come from carefully selected species of superweeds (Chandrasena, 2014; Guo et al., 2014; Cheng et al., 2015). The goal of this research is in part to open the eyes of agronomists and other scientists, who are involved in current space expedition planning, to recognize this overlooked source of plants as potential crops that contain some of the hardiest useful plants on Earth. Moreover, superweeds represent the progenitors of humankind’s most important cultivated vegetables and grains (Cheng et al., 2015) from which countless new crop varieties can someday be produced. As for the hardiness of superweed crops, despite a century-long war waged on them, costing billions of dollars annually in the development and application of potent toxic herbicides, superweeds have only become stronger and more ubiquitous around the globe (Bonny, 2016). It makes great sense then to look closely at the plants that cannot be so easily killed (Fennimore & Bell, 2014), and to do so in a concerted effort to determine what valuable products selected superweeds can offer in respect to the necessities and wants of human life during the early years of Mars colonization.

 

INCLUSION-EXCLUSION CRITERIA

This research began with a list of 263 species of plants (152 dicots and 111 monocots) that had been officially categorized as being “superweeds,” according to the International Herbicide-Resistant Weed Database (Heap, 2021). Preliminary research was accomplished on every listed superweed by checking it against a major edible and useful plant database (Fern, 1997), as well as using published hardcopy compilations such as Sturtevant’s Edible Plants of the World (Sturtevant & Sturtevant, 1972) and Cornucopia II (Facciola, 1998). Where the useful qualities of superweeds were listed as being unknown, the list was duly refined. This first culling reduced the list of potentially useful superweeds down to 100 species worthy of further research. A deeper exploration of the significant usefulness of those 100 superweeds, as well as an exploration of the advantageous cultivation details of those plants, allowed the remaining superweed candidates to eventually be pared down to 12 primary species for top consideration as Mars crops, and another 24 secondary useful species that are highly worthy of consideration. The final reduction was accomplished by using an instrument developed by the author of this research study, known as the Ten Critical Criteria for the Selection of Superweed Plants as Potential Space Crops for Mars:

(1) The first important attribute for a superweed to be considered as a potential primary crop for the first Mars colonists is that it preferably be an annual. This criterion was considered important because annual crops produce their entire array of useful products in one growing season, which means that if a particular crop were to fail, there would still be a chance to determine the cause of the failure and then replant and harvest an entire new crop with a minimal loss of time. Therefore, biennials were excluded, unless a particular superweed crop plant was potentially capable of supplying enough of a useful product in the first season of its growth. Another exception to the preference of annuals was the occasional perennial superweed that was capable of producing an array of useful plant products year after year, so long as a majority of those products were also available during the first year of its growth.

(2) A related inclusion criterion is that a potential superweed crop should have a relatively short life-cycle (Werle, et al., 2014). The importance of this criteria is that a crop could germinate and produce seed in a minimal amount of time, allowing a maximum number of harvests per year. Also, the sooner that usable plant products are available, the safer the situation will be for Mars settlers dependent on fresh food and plant-based industrial supplies. The quickness of the superweed products will also provide a very needed psychological advantage to the first colonists on Mars, who will be justifiably stressed about achieving sustainability (Earth-independence) until it actually happens. Short life-cycle crops may also help to alleviate the need for excessively rationing supplies, as would happen if Mars settlers were subsisting solely off supplies they brought from Earth.

(3) It was decided that the best superweed candidates for space crops would be those that were not aquatic in nature. Since water will most likely be a limited resource in the early years of Mars settlements, the most useful first superweeds will be those that grow on land with minimal water requirements. The time and resources required for building and maintaining artificial ponds and marshes will not likely happen in the first few years of colonization. For this reason, aquatic plants were excluded from consideration. While no aquatic superweeds made the primary cut, there was one superweed listed that produces best in moist soils but possessed the remainder of the inclusion criteria, see barnyardgrass (Echinochloa crus-galli).

(4) Likewise, superweeds that are solely found in tropical or temperate rainy environments were excluded from the list due to their excessive moisture, humidity and shade requirements. Moreover, tropical superweeds suffer the problem of lacking hardiness in cooler growing conditions. This could be an important factor in the choosing of the first primary crops for space settlers, since short-duration temporary system failures are likely to occur in the beginning stages of hammering out the glitches in technology-based settlements. Therefore, a majority of the superweeds selected during this study are those that can thrive in temperate hardiness zones.

 (5) Reproductively, an important trait for primary superweeds is that they be hermaphroditic in nature, able to self-pollinate due to possessing both male and female organs within the same flower. Only one superweed in the primary list was not hermaphroditic, but was monoecious instead, and therefore it still produces male and female reproductive organs on the same plant. To require a dioecious male and female plant of the same species for reproduction is to require excessive growing space by being forced to devote crucial resources for plants that might be useful only for pollination. While not all hermaphroditic or monoecious superweeds are self-pollinating, in most cases they are easily fertilized by using a soft paintbrush to spread the pollen from one superweed to another of the same species.

(6) It could be said that the solar system in which Earth revolves is mostly a desert. Therefore, there is a distinct advantage to crops that are destined to be relied upon for self-sufficiency when they are composed of those types of superweeds that can tolerate a wider range of soil pH than most cultivated crops, and especially when those superweeds are able to thrive in excessively alkaline soils.

(7) Superweeds that can thrive in poorly textured soils, such as clay or sandy soils that represent less than ideal drainage, make prime candidates for being classified as potential primary crops, especially considering the amount of sand and dust that is found on the surface of Mars, and the time it will take to build up an adequate supply of organic materials to amend Martian soil.

(8) In the event that there existed two closely related superweeds that were useful in similar ways, except that one of the species was considered somewhat superior for the same products it produced, the slightly less desirable species was excluded.

(9) Seed-bearing and propagating traits are important factors in determining the most reliable superweed crops on which Mars colonists might depend. There are superweeds in the primary list of this study that annually produce up to 2,000,000 seeds per plant, and whose seed viability has been demonstrated to last 40 or more years (Fennimore & Bell, 2014).

(10) Last but not least, a determination was made as to whether any certain superweed was found only on the east coast or whether it also occurred in the western half of the United States. If a certain superweed was documented as growing throughout the lower 48, it was considered to be a sign of adaptability and hardiness, and was likely listed as one of the top 12 potential superweed crops. If a superweed only occurred on the east coast, it was generally excluded. Conversely, if a superweed only occurred in the west, it might be included. The advantage of western superweeds is that they have demonstrated an ability to grow in soils with less organic materials, they can thrive in drier environments, and they are often hardy enough to be productive in either extreme hot or cold ecosystems.

A lack of one or two of the above criteria was not necessarily a conclusive factor to cause a potential superweed crop to be excluded from the primary list, but such criteria provided a frame of reference for establishing preferences. Certainly, any edible or otherwise useful superweed that possessed all the traits listed above was included in this list as having primary superweed crop potential. However, it should also be kept in mind that some of these exclusions are temporary in nature, and once a thriving colony has adequate resources, more growing space, increased carbon dioxide and a greater abundance of organic materials and water, an advanced agricultural phase of self-sufficient Mars colonization could allow more intensive farming of superweed crops with slightly less potentials, such as those 24 superweeds listed as secondary choices due to their extra cultivation requirements or for producing a more limited array of products. Likewise, once farming resources expand to the point that it allows increasing latitude for experimentation, certain common commercial vegetables may be safely tested in greater quantities, though only experience will tell whether more modern crop plants will be able to be dependable enough to eventually be considered as potential primary crops themselves.

 

Table 1. Top 12 Superweeds with the Highest-rated Useful Properties for Space Crops.

Top 12 Superweeds
Barnyardgrass (Echinochloa crus-galli)	Birdsrape mustard (Brassica rapa campestris)	Black Nightshade (Solanum nigrum)	Catchweed Bedstraw (Galium aparine)
Common Sunflower (Helianthus annuus)	Lambsquarters (Chenopodium album)	Livid Amaranth (Amaranthus blitum oleraceus)	Purslane (Portulaca oleracea)
Shattercane (Sorghum bicolor)	Virginia Pepperweed (Lepidium virginicum)	White Mustard (Sinapis alba)	Wild Radish (Raphanus raphanistrum)

 

 

Super Traits of Primary Superweed Crop Candidates

A concise summary follows below, supplied in two sentences per superweed, to briefly describe some of the more useful qualities of the 12 superweeds that have been suggested for consideration as having the highest potential for becoming primary crops on Mars:

Barnyardgrass (Echinochloa crus-galli) provides a profusion of edible seeds that serve as an excellent substitute for millet, and are even grown commercially in India as an important source of food. Barynyardgrass also possesses many medicinal possibilities, including potential anti-carcinogenic qualities.

Birdsrape mustard (Brassica rapa campestris) provides edible fresh or cooked greens, seeds which can be ground and made into a spicy condiment or used in pickles or curries, flowers that can be used to liven up a salad or used as a delicate broccoli substitute, and edible stems. Equally important, this superweed could be called the “mother of brassica crops,” since Brassica rapa is the crop wild relative (CWR) from which such commercially cultivated crops as bok-choy, Chinese cabbage, Chinese kale, mizuna, neep greens, rapeseed, turnip and turnip greens are derived (Weaver, 2013; Guo et al., 2014; Warschefsky et al., 2014; Cheng et al., 2015).

Black Nightshade (Solanum nigrum) is an annual that produces a highly edible fruit in one growing season from which many heirloom “garden huckleberry” varieties have been selectively developed. These berries, which are high in anthocyanins, when sweetened and cooked can be used as an excellent blackberry substitute for pies, sauces, and jams without the need for a fruit-bearing tree or bush that could take years to become productive.

Catchweed Bedstraw (Galium aparine) seeds, when lightly roasted, form one of the best coffee substitutes on Earth (or eventually off-planet), and the leaves make a good substitute for tea. Studies have shown that bedstraw is useful for weight loss, and artificial vanilla can be extracted from this plant to supply one of the world’s most popular culinary flavorings.

Common Sunflower (Helianthus annuus) could be considered to be one of the most useful wild edible plants available for humanity. Not only can the nutritious seeds be used in any way that nuts can be utilized in recipes, it also supplies a very edible and healthy oil for both cooking and industrial purposes, plus the unopened flower buds can be cooked and eaten as an artichoke heart substitute.

Lambsquarters (Chenopodium album) is considered superior in taste to spinach by aficionados, and supplies a prolific amount of seeds that can be germinated to use as delicious and healthy sprouts or microgreens (Choudhary & Sharma, 2014; Poonia & Upadhayay, 2015). The thick flowerheads also make a fine substitute for broccoli.

Livid Amaranth (Amaranthus blitum oleraceus) is a close relative of commercial types of Amaranthus that produce very edible leaves, plus it provides a wild form of the pseudo-cereal known as quinoa. This grain-like seed supplies a portion of all nine essential amino acids (for adults and children), making it a complete protein meat substitute that is also high in calcium.

Purslane (Portulaca oleracea) is a superweed that qualifies as a superfood, being particularly high in iron, vitamins A and C, and contains more omega-3 fatty acids than any other vegetable on earth (Uddin et al., 2014; Petropoulos et al., 2015), which is why it is increasingly becoming a more common product for sale in farmer’s markets. During the night, purslane develops significant amounts of malic acid, which is the main flavor found in green apples, meaning that apple-like desserts could be made from the cooked leaves or stems of purslane.

Shattercane (Sorghum bicolor) produces a very sweet syrup that can be used as an excellent sugar and molasses substitute. The profusion of round, pinkish seeds can be cooked and used in ways similar to barley, millet, rice, or ground into a fine white flour for making breads and cakes, and also makes good sprouts for salads or stir-frys, besides possessing medicinal qualities useful in treating kidney and urinary complaints.

Virginia Pepperweed (Lepidium virginicum) is one of the most “peppery” superweeds of all, whose seeds have long been referred to as “poor man’s pepper,” and which have also been used medicinally as a cardiotonic, an effective cough suppressant, and for its anti-protozoal qualities. A puree of the pungent leaves makes a good mustard substitute, while the ground roots can be satisfactorily used in lieu of horseradish.

White Mustard (Sinapis alba) forms the source of the mustard flavor that is popular in American casual cuisine on cold meat sandwiches, hamburgers, hot pastrami, and hotdogs. Many wild members of the mustard family possess the prime requisite for off-planet pioneers in that they have very short-life cycles, producing an array of useful products and then going to seed, even in some cases, in less than a month.

Wild Radish (Raphanus raphanistrum) lives up to the name except for its lack of producing the familiar fleshy taproot that is most associated with this vegetable. Wild radish, on the other hand, produces a large amount of edible leaves, edible flower buds, edible petals, edible pods, and edible seeds that can either be ground or toasted or used as pungent sprouts or pressed for oil; and the long white roots can even be peeled and cooked as a taste substitute for kohlrabi.

 

Six Significant Challenges to Farming on Mars

Despite the ease with which superweeds can usually grow, soil and atmospheric conditions on Mars represent a tremendous challenge for any living organism (Karoliussen et al., 2013). The challenges facing off-planet farmers, especially on Mars, emphasizes the inherent risks of relying solely for subsistence on those cultivated crops typically found in American grocery stores, due to the special care required in sowing, watering, and fertilizing cash and truck crops, even under the best conditions on Earth. If the propagation and cultivation of common garden vegetables and grains were easy, there would not be so many books, classes, clubs and websites available on the topic, nor would shelves at nurseries be crammed full of starter plants every Spring. Add the six nearly unsurmountable challenges of growing plants on Mars, and it can quickly be seen why those crops that grow with the least assistance and supplements could represent the best choice of primary crops for the Red Planet.

(1) NASA, aerospace corporations, National Space Society members, Mars Society members, plus a wide range of university research institutions have been diligently working to develop the technological means by which to grow a sufficient amount of crops in space colonies (Walkinshaw & Galliano, 1990; Morrow, 2014), since the obstacles to doing so are profound. In the case of Mars, its atmospheric components at first appear somewhat acceptable for plants, since the air is composed of 95% carbon dioxide, 2.8% nitrogen, 2.0 % argon, 0.174% oxygen, and 0.03% water vapor (depending on the season). While this ratio of gasses might seem capable of supporting plant life, Mars possess a very thin atmosphere, whose surface pressure amounts to less than 1% of the barometric pressure found on Earth (Mahaffy et al., 2013). What this means is that there is only a modicum of those named gasses detected, even when the percentages sound reasonable.

(2) Likewise, soil on Mars has been found to be devoid of organic materials, and is basically composed of two parts crushed volcanic rock, two parts oxidized basalt dust, and one portion of sand (Allen et al., 1998; Wan et al., 2016: Scheerbaum, 2000). When adding water to such a mixture, it has been reported to create Martian concrete.

(3) A recent challenging discovery to do with Martian soil is that the dust contains up to 1% toxic calcium perchlorate. On the plus side, since calcium perchlorate is useful in attracting water molecules and for producing oxygen, it could be a beneficial find overall for humans, but is less than an ideal growing medium for plants. Moreover, a fairly recently published experiment showed that calcium perchlorate, when irradiated with high intensity UV rays, such as those commonly striking the surface of the Red Planet, and when occurring in combination with the high percentage of iron oxides found in Martian soil, becomes bactericidal in nature (Wadsworth & Cockell, 2017), which is not good news for agriculture. Basically, this finding reveals that the soils of Mars are much less hospitable to life than what was even previously imagined (Quinn et al., 2013; He et al., 2021).

 

Starlight, Starlight Everywhere but Not a Ray of Warmth

(4) To add to the complexity of farming on Mars, sunlight is the driving force for photosynthesis in plants, whether they are crops or not, but when it comes to the topic of sunlight, another challenge that concerns Mars is that the “fourth rock from the Sun” orbits much further away from the solar system’s main source of light than does Earth. While the third rock from the Sun orbits at a distance of one astronomical unit (AU), Mars’ orbit averages 1.524 AU’s, and therefore the Red Planet receives only 44% of the intensity of sunlight as Earth (Sagan & Pollack, 1974). To add to the complexity of agriculture on Mars, the Red Planet follows a very eccentric orbit, causing Mars to be much closer to the sun at perihelion (206.7 million kilometers) and much farther away at aphelion (249.2 million kilometers).

(5) Moreover, temperatures on Mars are extremely colder than Earth, due in part to receiving less intense sunlight and in part due to a dearth of greenhouse gases that help hold in the heat (Biswal et al., 2021). Accordingly, the average temperature on Mars has been estimated to be -81 degrees F., whereas the average temperature on Earth is presently estimated to be 59 degrees F (140 degrees warmer). When reviewing Martian weather data, winter temperatures on Mars at the poles is -243 degrees F., while the warmest possible temperature estimated for Mars is believed to be 68 degrees F for an infinitesimally brief period of time at the equator, during optimal sunlight, at the height of a Martian summer. At night, those temperatures would drop far below zero degrees F.

(6) Despite its distance from the Sun, Mars receives far more harmful radiation on its surface than Earth, due to having no protective magnetosphere or ozone layer to capture deadly cosmic rays in its thin atmosphere (Matthia et al., 2017). In 2001, the Mars Odyssey probe recorded radiation levels on Mars that were 2.5 times higher than what astronauts experience on the International Space Station. To put it in Earth terms, an average Earthling is exposed to approximately 0.62 rads of cosmic radiation per year, while astronauts on the International Space Station receive around 8.03 rads annually. That being said, Odyssey recorded radiation spikes on Mars (during solar proton storms) as high as 2 rads in a single day (about 1,176.47 times greater radiation than a normal day of exposure on Earth).

Considering the thin atmosphere, toxic inorganic soils, extreme cold, reduced light intensity, and deadly UV radiation, successful farming on Mars will require considerable technological advancements in growing chambers for crops to survive, which will likely include artificial full-spectrum lighting in heated underground caverns (possibly in lava tubes) that are protected from the extreme cold, as well as from seasonal dust storms and the intense unprotected cosmic radiation from the Sun. Suffice it to say that until the Red Planet is terraformed (Fogg, 1995), there will not be any attempts at dry farming outdoors.

 

Table 2. 24 Superweeds with the Second Highest-rated Useful Properties for Space Crops.

24 Superweeds
Buckhorn Plantain (Plantago lanceolata)	Burning Nettle (Urtica urens)	Chickweed (Stellaria media)	Common Sowthistle (Sonchus oleraceous)
Corn Poppy (Papaver rhoeas)	Crystalline Iceplant (Mesembryanthemum crystallinum)	Feral Rye (Secale cereale)	Field Pennycress (Thlaspi arvense)
Horseweed (Conyza canadensis)	Johnson Grass (Sorghum halepense)	Kochia (Bassia scoparia)	Large Crabgrass (Digitaria sanguinalis)
Musk Thistle (Carduus nutans)	Pineappleweed (Matricaria discoidea)	Prickly Sowthistle (Sonchus asper)	Prostrate Knotweed (Polygonum aviculare)
Russian Thistle (Salsola tragus)	Sheep Sorrel (Rumex acetosella)	Shepherd’s Purse (Capsella bursa-pastoris)	Sterile Oat (Avena sterilis)
Redroot Pigweed (Amaranthus retroflexus)	Wild Carrot (Daucus carota)	Wild Chamomile (Matricaria recutita chamomilla)	Yellow Nutsedge (Cyperus esculentus)

 

 

IMPLICATIONS

Self-sufficiency is the difference between temporarily exploring space and colonizing it. Without properly choosing the best suited crops to increase the chances of a constant and renewable supply of plant-based resources for space colonists, visits to Mars will be brief affairs, likened to visits to the summit of Mt. Everest. An impressive challenge will have been met for the record books, but no significant benefits would have accrued for advancing the territory of humankind. This study on Earth’s most overlooked potential crops – that are being recommended for at least the first few years of Mars colonization – has been accomplished in order to open the eyes of today’s space settlement planners to the immense potentials inherent in the agricultural assets known as superweeds. Furthermore, this study has attempted to demonstrate that carefully selected crop-worthy superweeds could possess the potentials to allow off-world colonists to survive and thrive more assuredly than if they were attempting to seek self-sufficiency solely by utilizing modern cultivated crops whose growing requirements demand far more intensive labor and resources.

Besides exploring the qualities that qualify hardy superweeds as being useful crops on Mars, equally important is the criteria that was developed to narrow the list of 263 superweed species, including 100 superweeds with useful properties, down to 12 superweeds that are most highly recommended for space colonists in their first few years of farming. It was these same criteria that also consolidated the list of 24 secondary useful superweeds worthy of consideration. Accordingly, the implications of the selection tool created for this study might assist space scientists in making more informed decisions when choosing crop species other than superweeds for establishing Earth-independence. As such, this space crops selection instrument narrows the best potential primary space crops down to those that offer the quickest useful products and the lowest chance of crop failure, which are vital considerations for off-planet populations on Mars where the replenishment of new seeds and plant stock could take two years or longer to procure.

 

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