Future astronauts spending Thanksgiving in space may not have to forgo one of the most traditional parts of the day's feast: fresh sweet potatoes.
Cary Mitchell, a Purdue University professor of horticulture, and Gioia Massa, a former postdoctoral researcher at Purdue, developed methods for growing sweet potatoes that reduce the required growing space while not decreasing the amount of food that each plant produces. Their findings were published in the journal Advances in Space Research.
Sweet potato plants have main vines with many shoots that branch out to the sides. Mitchell said it was common for one plant to cover the entire surface of a 15-by-5-foot greenhouse bench.
"Sweet potato is like an invasive plant. It will take over everything," said Mitchell, who studies the selection of crops that could be grown in space. "That's not acceptable if you're going to grow it in space."
Knowing they needed to contain the plant's horizontal spread, Mitchell and Massa decided to force it to grow vertically. Using cones or cylindrically shaped wire cages, they trained plants' main vines to wrap around the structures while removing the space-consuming side shoots.
"It turns out the vines are not really picky about what you do with them," Massa said. "As long as you leave the main shoot tip alone, you can remove the side shoots and trim them away without any yield loss."
The main shoot tip, or the end of the main vine, is the only really sensitive part. It sends hormones throughout the plant that stimulate root development, which is important since it is the roots that become the sweet potatoes.
The side shoots, if picked when still young, are tender and can be eaten in salads, improving the plant's usefulness, Mitchell said.
On Earth, scientists might want to find ways to get crops to take up less area, focusing on only two dimensions. A tall, skinny corn stalk, for instance, takes up little space in a farm field.
In space, however, that third dimension - height - is important because plants may need to be stacked to use all available space. Using a cone or cylinder is what might make sweet potato a viable space crop. Since the area inside the cages is empty, astronauts could put other plants inside and keep them alive with LED lighting.
The sweet potato plants also weren't particular about lighting or temperature. Mitchell and Massa grew sweet potatoes in greenhouses during different seasons and saw no difference in yield.
"Sweet potato doesn't seem to care what season it is or what conditions it's in," Mitchell said.
Massa said that's important because many different types of crops may have to be grown in the same rooms in space. Picky plants won't fare well with other picky plants having temperature or lighting requirements much different from their own.
"We call it a generalized-growth environment," Massa said. "We're finding the optimum, not the maximum."
Mitchell and Massa said they'd next like to study LED lighting's effect on sweet potato and other crops. NASA funded their research.