How does a kitchen gardener choose what to grow? It’s about balancing quite a complex set of variables, which include the space and time available, the local climate and soil, the gardener’s skill level and what they like to eat. That last one is, itself, quite a complicated topic as culture plays a significant role. There are many thousands of edible plants on the planet; most people only eat a small number and grow fewer still.

A gardener may choose to grow crops which produce the largest amount of food, or the greatest financial value of food, or the widest variety of food, or simply an assortment of exciting plants. And when a gardener has decided which species to grow, they then have to choose between varieties!

Veggies!

Choosing crops for a space garden is no less tricky. On the International Space Station, for example, space and power are both limited, and there’s a finite supply of water. It’s expensive keeping astronauts on the ISS, and their time is strictly controlled to make them as productive as possible, so leisurely gardening is pretty much out. Plants need to be compact, low-maintenance, fast-growing and productive while being tasty and nutritious. There are concerns about microbial growth, so there’s that, too. Oh, and there are no real cooking facilities on the ISS, so they’re basically limited to things that can be eaten raw.

When they were planning the Veggie growth system for the ISS, NASA investigated which species to grow in it. They were looking for leafy vegetables with good growth and nutrition, which the astronauts would enjoy eating.

Veggie is Up and Running! (NASA, International Space Station, 05/13/14)
NASA astronaut Steve Swanson installed Veggie on the ISS in May 2014, and started growing the first batch of Outredgeous lettuce
[Image credit: NASA]

They picked (and it’s not yet clear to me why) eight varieties to trial: ‘Tyee’ spinach , ‘Flamingo’ spinach , ‘Outredgeous’ Red Romaine lettuce, ‘Waldmann’s Dark Green’ leaf lettuce, ‘Bull’s Blood’ beet, ‘Rhubarb’ Swiss chard, ‘Tokyo Bekana’ Chinese cabbage, and Mizuna. They’re all commercially available in the US. If you’ve been keeping up with events on the space station, you’ll know that some of those have been grown, and some of them haven’t.

The eight varieties were all grown in conditions similar to the ones they would find on the space station, so that things like height, spread and yield could be evaluated. The researchers measured the levels of minerals in the harvested leaves – calcium, magnesium, iron and potassium. For three of those they wanted high values, but in microgravity, high iron levels are associated with bone loss, so lower iron levels are better. The beetroot leaves had the highest iron levels by a significant margin, followed by the Swiss chard and the two spinach varieties (which, you will note, are all part of the same botanical family).

Grow your own space lettuce! Outredgeous seeds are available from Suttons in the UK

Four candidates made the shortlist – Tokyo Bekana Chinese Cabbage, Rhubard Chard, Mizuna and Outredgeous lettuce – and their leaves were sent for more detailed nutritional testing. This time they were analysed for phytochemicals – anthocyanins, carotenoids, and vitamin K levels. Anthocyanins are anti-oxidants, the carotenoids are good for eye health, and the astronauts’ diet is known to be deficient in vitamin K (and potassium). Only the chard and the Outredgeous lettuce had anthocyanins, as they’re not present in all-green leaves. The chard also had the highest levels of the carotenoids. For vitamin K and calcium, Mizuna was the clear winner.

A tasting panel convened to munch on the four shortlisted crops and score them for appearance, colour intensity, bitterness, general flavour and texture. All four scored at least 6.5 out of 9.

The NASA researchers then assigned each variable a weighting factor and crunched the numbers. The Chinese cabbage came top. It had excellent rapid growth and good nutrition and proved popular with the tasters. The Swiss chard came second, with excellent nutrition but slower growth. In third place, Mizuna was fairly nutritious and palatable but had excellent growth. The ‘Outredgeous’ lettuce struggled with storage and shipping, which would not be a problem on the ISS, but it had good growth, good nutrition and generally good palatability (it was a bit wilted).

We know that the first crop to be grown in Veggie (and the second) was the Outredgeous lettuce. The third was Zinnias for their flowers. By April 2019, astronauts had also used Veggie to grow two more varieties of lettuce (Waldmann’s Green and Dragoon), the Tokyo Bekana Chinese cabbage, Mizuna and Red Russian kale

The NASA scientists are planning more crops, including tomatoes and peppers. They’re looking into growing other foods – berries, some beans and other antioxidant-rich plants – that they think would provide astronauts with some protection against space radiation. At least that’s one thing Earth-bound gardeners don’t have to worry about!

Space lettuce seeds from Suttons

Reference

Massa, Gioia D., et al. “Selection of leafy green vegetable varieties for a pick-and-eat diet supplement on ISS.” 45th International Conference on Environmental Systems, 2015.