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Blue Sky Science: How long does it take for a tree to grow in space?

January 23, 2019

Q How long does it take for a tree to grow in space?

— Stella Newhouse, Prairie du Chien, Wis.

A Simon Gilroy, professor in the botany department at the University of Wisconsin-Madison:

It’s a complicated question because, while researchers have grown spruce seedlings on the International Space Station, they haven’t grown full-size trees. Using knowledge of how trees operate on Earth, scientists can guess what’s going to happen when they’re grown in space.

The tallest trees on Earth are the giant redwoods that are about 300 to 400 feet tall. Gravity is the main reason those trees are not any taller.

For a tree to get that massively tall, it has to be strong. Tree height is also limited because trees must draw water from the ground up to their leaves. As the water is pulled up through the plant, at some point the water column gets so long that it’ll break because of gravity.

In space that problem doesn’t exist. Without gravity, plants growing on the space station grow long and thin and don’t need to lay down a lot of supportive tissue. Plants can draw water more easily — because there’s no gravity pulling on the water column — and get large without weighing anything.

In theory a tree could get massively tall in space, but there are still the practical limitations. Giant sequoias obviously would not fit inside a space station; it’s unlikely they will ever be grown in space.

Could trees be grown on the moon or Mars? Perhaps. The minerals in the soil on the moon or Mars are not quite the right composition for growing plants. But it’s possible, and the reduced gravity would likely make them grow a lot taller.

Also, plants use gravity to direct their growth. Classically, shoots grow up and roots grow down. Take away gravity as a cue for where to put roots, and you have one set of confused plants.

Scientists on the space station have been trying to figure out how long it takes to grow a generation of plants in space, whether a tree grows like it does on Earth and other questions.

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