In 2021, NASA grew Hatch chile peppers on the International Space Station; over 137 days, the plants produced harvestable fruit with unusually straight stems

Under normal conditions on Earth, the plant would not need to know which way is up since the roots go down and the stems grow towards the sky, and all of it is maintained by the help of gravity. Without that force, things become unclear, though. This fact was illustrated in the experiments done by NASA astronauts who grew Hatch chile peppers on the International Space Station in 2021.

According to NASA’s official records on the mission, the Hatch chile peppers spent 137 days growing in orbit and produced a harvestable crop. Moreover, the stalks of the plants grew to be unusually straight, unlike those growing on Earth. While it seemed like just another space experiment, in fact, it was just a tiny part of a larger issue concerning whether astronauts would ever be able to grow something to eat during their long missions away from home. The answer was yes.

The experiment that outlasted everyone's patience


The experiment was called Plant Habitat-04 (PH-04). NASA astronaut Shane Kimbrough inserted 48 sanitized Hatch chile seeds into the station's Advanced Plant Habitat on July 12, 2021, and the mission concluded 137 days later, on November 26, 2021. NASA's own account of the mission described it as one of the longest and most complex plant experiments attempted aboard the space station to that point. Only four of the 48 seeds grew into plants, inside a cultivation chamber about the size of a large microwave, and the team collected 26 chile peppers across two harvests.

Astronaut Mark Vande Hei brought in the first batch of seven peppers on October 29, and Megan McArthur turned some of them into what she described as her best space tacos ever. The second harvest, on November 26, yielded the remaining 19 peppers, 12 of which were packaged and sent back to Earth for lab analysis, with the rest sampled fresh by the crew. NASA credited that second harvest with breaking its own record for feeding the most astronauts from a single space-grown crop. However, there is one tiny caveat for the purists: because the plants weren't grown in New Mexico's Hatch Valley, they can't officially be called "Hatch chiles," even though the cultivar itself, NuMex 'Española Improved,' is a hybrid Hatch pepper developed at New Mexico State University by crossing the 'Hatch Sandia' pepper with the traditional 'Española' pepper of northern New Mexico.

Why the straight stems actually matter

Plants on Earth have an in-built compass known as gravitropism, which explains why the stems grow upwards while the roots grow downwards regardless of how one places the seed. Without gravity, that directional cue is removed. According to a 2025 study titled “Exploring plant responses to altered gravity for advancing space agriculture,” published in the journal Plant Communications, gravitropism is understood as a multi-step process involving gravity sensing inside plant cells, a signaling cascade, and a hormone-driven curvature response, and the review notes that plants grown in microgravity have been observed, across various experiments, to show random root growth direction, larger branch angles, delayed flowering, and smaller seeds. The loss of a consistent "down" signal may help explain the straighter growth NASA observed in its space-grown peppers, though the review itself was not a study of the PH-04 peppers specifically.

Additionally, several studies in the field of space biology have shown that reduced gravity can affect plant directionality, including root skewing and delayed flowering. That lines up with what NASA reported for PH-04 itself: principal investigator Matt Romeyn noted that the space-grown peppers' flowering and fruiting ran about two weeks behind the mission's original ground-based timeline, which, along with the unusually straight stems, he called a clear microgravity effect.

About that "spicier in space" claim

It's quite possible that you saw the media reports in 2021 talking about how the peppers grown in space were hotter than normal. Just to clarify the situation at this point: According to Matt Romeyn, the principal investigator at NASA, astronauts reported that the fruits tasted a bit spicier, which he called "not unexpected." NASA's own pre-mission materials had flagged microgravity as a potential stressor on the plants that could plausibly affect heat level. But taste is a sensory report, not a chemical measurement, and there are no published results confirming that capsaicin, the compound that actually makes peppers hot, increased during the flight. So the "spicier in space" claim remains unproven rather than confirmed, and it's also not necessarily a myth: astronauts' perception of taste in microgravity is known to shift for other physiological reasons, such as fluid redistribution affecting the sinuses, independent of anything happening in the pepper's chemistry.

Why should this matter

Researchers focusing on low gravity continue to note that growing food on the Moon and Mars will require understanding how plants respond under reduced gravity, not just whether their seeds will sprout. A 2021 paper titled “Understanding Reduced Gravity Effects on Early Plant Development Before Attempting Life-Support Farming in the Moon and Mars,” published in the journal Frontiers in Astronomy and Space Sciences, notes that the reduced-gravity conditions may increase the responsiveness of the plants to such stimuli as light and water; however, it remains unnoticed on Earth due to the domination of gravity. In that light, the straight stems on NASA's space-grown peppers are one small data point in a much larger question: what will it actually take to grow food off-world, at a time when food security is already a growing concern back on Earth.