Here’s How NASA Astronauts Grew Perfect Peppers on the ISS

In the 2015 blockbuster movie "The Martian", a botanist-turned-astronaut gets stranded on Mars and must find ingenious ways to survive the dire situation. He, somehow, survives — thanks to the power of the humble potato.

His brilliant plan involves fertilizing Martian soil with his feces, chopping potatoes, and planting the cuttings in the soil. This eventually gives him enough food to last hundreds of days, aiding his survival in desperate circumstances.

But let’s not get ahead of ourselves — before we can dream about cultivating plants in Martian soil, we need to get agriculture as we know it to space. And that’s exactly what NASA scientists and astronauts on the International Space Station (ISS) are doing, one pepper at a time.

As the chile pepper season came to a close in New Mexico’s Hatch Valley after a long and scorching summer, a first-of-its-kind harvest took place miles above Earth on the ISS, where an astronaut collected a number of mature peppers in late October.

Happy pepper picking day aboard the @Space_Station!?️Today @Astro_Sabot gets the honor of harvesting the station’s first crop of chile peppers as a part of the Plant Habitat-04 study, one of the most challenging station plant experiments to date. https://t.co/f1LHkidhFn pic.twitter.com/dim8uHNZbs

— ISS Research (@ISS_Research) October 29, 2021

Now, that experiment, which was a part of the Plant Habitat-04 (PH-04), has come to an end, 137 days after it began in microgravity. On Nov. 26, several of the chile peppers (Capsicum annuum) grown from four plants in the orbiting laboratory's Advanced Plant Habitat (APH) were harvested and sampled.

This is the longest experiment on the space station to date. It's also one of the most challenging ones due to the long germination and growing time of the peppers.

"With this experiment, we took a field cultivar of a Hatch chile pepper from New Mexico, dwarfed it to fit inside the plant habitat, and figured out how to productively grow the first generally recognized fruiting crop in space – all in a span of a couple of years," explained Matt Romeyn, principal investigator for PH-04 from NASA’s Kennedy Space Center, in a press release.

Somewhat endearingly, PH-04 also broke the record for feeding the most astronauts from a crop grown in space. The peppers were reported to be spicy, vibrant, and delicious — and perhaps most importantly, they are rich in vitamin C.

This is significant since astronauts aboard the ISS currently rely on regular shipments of freeze-dried and prepackaged meals to meet their dietary needs. When crews venture further into deep space, they'll be traveling for years without receiving resupply shipments. This could spell health troubles for the astronauts since vitamins in prepackaged form break down over time.

Remember that a lack of vitamin C for four weeks or more was all it took for sailors to develop scurvy, a disease that ravaged ships' crews during the Age of Discovery. And as we engineer missions to reach Mars and beyond, astronauts will need to spend much longer than three months in space. Simply packing some multivitamins will not be enough to keep astronauts healthy for the entire trip, so they'll need nutrients in a long-lasting, easily absorbed form such as freshly grown fresh fruits and vegetables, which is why experiments like PH-04 are being conducted. 

This is also where NASA’s Vegetable Production System, known as Veggie, and Advanced Plant Habitat comes in.

Engineering ingenious space gardens

NASA has been studying how we can grow plants in space for decades, and to date, astronauts have eaten nine types of leafy greens grown in Veggie, as well as two crops, radishes, and peppers, grown in APH.

In fact, the Veggie space garden, which is roughly the size of a carry-on piece of luggage, has grown a variety of plants, including three types of lettuce, Chinese cabbage, mizuna mustard, red Russian kale, ​and zinnia flowers. They’ve apparently all been delicious — and most importantly, safe to consume.

To tackle the monumental task of growing crops in space without sunlight or gravity, Veggie has been engineered to house plants growing in a "pillow" filled with a clay-based growth media and fertilizer. The pillows help distribute water, nutrients, and air in a healthy balance around the roots. That's incredibly important, as the roots would either drown in water or be smothered by air due to the way fluids in space tend to form bubbles.

Because of all that, water management has been one of the biggest challenges for the space agency’s plant experiments, according to NASA APH program manager Nicole Dufour, who spoke with Interesting Engineering in a video interview.

Managing water carefully is especially important with a passive system such as Veggie, whereas APH is completely automated and employs LED lighting and a porous clay substrate with controlled release fertilizer to deliver water, nutrients, and oxygen to the plant roots.

"It took a few years of experimentation in microgravity to get the hang of it, but practice makes it close to perfect," explained Dufour. "With our teams carefully monitoring the data and making adjustments as needed, we’re able to grow beautiful, healthy plants on the ISS."

APH is different from Veggie in a number of ways. The system is enclosed and equipped with cameras and more than 180 sensors that are in constant contact with a team on the ground at Kennedy. Its water recovery and distribution systems, as well as its atmospheric content, moisture levels, and temperature are completely automated, so it doesn’t require much day-to-day care from the ISS crew.

When it comes to facilitating growth without gravity, plants are able to use other environmental cues, such as light, to orient themselves and guide growth. APH comes with a bank of LEDs above the plants, which emits a spectrum of light suited for the plants’ growth. Since plants reflect a lot of green light and absorb more red and blue wavelengths, the Veggie chamber glows magenta pink most of the time.

"APH is more capable than Veggie, so we use a mixture of red, green, blue, and white [light]," explained Dufour. "We actually studied this mixture beforehand to be able to dwarf the plants a little bit. They could definitely grow larger and taller — so we used the lights to make them grow smaller but still be productive."

Ground control to Major Tom — How does your garden grow?

Still, at the end of the day, all gardens, whether in space or not, require some love and attention, which means some astronauts need to fill the role of a devoted gardener on the ISS. And while an astronaut's steady hand is good for the plants' wellbeing, the benefits go both ways, as gardening in space contributes positively to the health and psychological well-being of the astronauts. Indeed, many astronauts have reported that caring for the plants was an enjoyable and soothing task.

I loved getting my hands on the pepper plants and pollinating them! I felt a much higher-than-usual level of focus compared to tending plants on Earth. Of course I played Red Hot Chili Peppers for them! :hot_pepper: See why we are growing this complicated crop: https://t.co/7YJ8yfrRfP pic.twitter.com/8MnpLVbYoA

— Megan McArthur (@Astro_Megan) September 14, 2021

Also, since astronauts lose some of their sense of taste and smell as a result of living in zero gravity, spicy or well-seasoned foods are particularly popular menu selections.

However, one of the biggest impacts of the project, according to Dufour, is hidden in the non-verbal cues that show the astronauts really enjoy caring for the plants. "All of the crew we’ve interacted with have thanked us for allowing them to work on the project, but what sticks with me the most is when I sit in the operations room and watch the astronaut come to do their tasks, I basically see their whole emotional state change. They could’ve been doing something boring before, but I can tell they’ve been looking forward to whatever they’ll be doing with the plants."

And it appears that the enticing power of the plants has a way of taking a hold on the entire crew. "Once the plant chamber is opened, there are usually other astronauts coming to see what’s going on," Dufour said. There’ve been cases of very minor plant theft, too. "We sometimes remove pieces from the plants while tending them, and we've had crew members who sneak off with the little cuttings, and take them as a little souvenir because they just enjoy it so much."

This bond takes on a whole new level when the plants bear fruit and astronauts finally get to taste the fruits of their labor through delicious meals. When a harvest is ready, the crew freezes or chemically fixes samples from the plants to preserve them and sends them back to Earth to be analyzed so scientists can better understand how space influenced their growth and development.

But if you were presented with two peppers, could you tell which one was grown on the ISS? We can tell you that wouldn't be an easy task for the uninformed eye, since it was seen that the plants grew similarly on the space station and on the ground, although there have been a few key differences.

"The biggest difference I’ve noticed is with the peppers," said Dufour. "This particular pepper has a very distinctive j-hook shape. But with microgravity, the fruits didn’t form a j-hook, and they were pointed in different directions. This could be a gravity-specific reaction for this plant, which would not be observed in orbit."

Scientists have already seen two differences between @Space_Station and Earth grown chiles?️:
-The peppers’ germination was delayed by ~two weeks on the @Space_Station
-The stems connecting the flowers and fruit were completely straight, rather than curved https://t.co/LZfGGHvYUc pic.twitter.com/K54Wmubwrg

— ISS Research (@ISS_Research) December 1, 2021

The leafy greens grown on the ISS, on the other hand, tended to spread out more, and "look more free," as they were "not restrained by gravity", explained Dufour. "We’ve also noticed that, with all of our crops, there is probably a few days to a week delay in the growth rate. This isn’t a huge impact, but it’s still a difference."

When the chile peppers return to Earth, the PH-04 team at Kennedy will focus on evaluating the data and investigating samples from the ISS to determine how well they grew and how they can further optimize growth.

"We will be measuring the capsaicin content in these peppers to see how spicy they are. We’ll also be evaluating the seeds from the fruit that were returned, and see if we can germinate some of them," explained Dufour. "We'll also be looking at the nutritional value and evaluating those levels compared to fruit we grow on the ground."

In case you were wondering, no, the ground-based researchers won’t get to do taste tests on the space peppers when they come back. But they did do some form of taste testing, "before we sent these varieties up — which is about as close we can get. But the astronauts seem to clearly have enjoyed them."

What’s the next interstellar plant?

Following the success of the PH-04 peppers, the researchers want to cultivate dwarf tomatoes and try different varieties of leafy greens as their next crop experiments. The team at Kennedy also has been establishing the framework for growing microgreens, legumes, and herbs on the ISS in the near future. The APH has a cotton experiment planned as well, and Veggie will host other plant tests before astronauts use it to grow more food to eat later.

We won’t see space gardens full of lush and fussy calatheas or sturdy succulents any time soon; however, we can expect NASA to scale up its little space farms in the future. "We are currently learning lessons from both Veggie and APH, which are at the two totally opposite ends of the capability spectrum," explained Dufour. "We are basically studying the trade-offs and benefits of both systems, and incorporating those into our plans for the future. The next project is going to be somewhere in between, in terms of capability."

Does this mean we’ll see Artemis astronauts feasting on tacos made with fresh ingredients as they travel to and from the moon? It’s likely. "I certainly hope we'll be seeing astronauts eating peppers, tomatoes, and whatever else we can come up with on all of the missions," said Dufour.

So when the ambitious deadlines are met to carry astronauts to the next chapter of the space exploration, they'll be carrying with them a souvenir of the pale blue dot they’ve left behind, in the forms of bright, nutritious fruits and vegetables — a taste of home.