DAVIDSON – It’s tough not to notice a two-layer contraption filled with green, leafy plants when passing by Kristin Metzler's classroom at Davidson Day School.

It’s a hydroponic garden – a soiless garden that can grow vegetation year-round and exponentially faster than outside.

“You don’t actually need the soil,” she said. “You need the nutrients from the soil, and you need something to prop up the plants with.”

Students use grow plugs – or brownies as they call them since the small, brown plugs are similar in shape and size to the baked treat – to start the plants.

For about a week and a half, the plugs are tended to in a nursery and kept under a blanket to force energy into the root system, Metzler explained. With the right level of humidity and heat, the seeds in the plugs germinate quickly, and the root system is long enough that they can be transplanted into the hydroponic garden.

In the garden, nutrient-filled water is pumped through a basin where the roots of the plants hang down. Grow lights are strategically placed throughout the garden. The amount of light used depends on the type of plants – for leafy greens, the lights can be on all the time, whereas plants that flower need at least eight hours of darkness, Metzler said.

Metzler uses the indoor garden as a tool for various classes and the school’s garden club.

Her middle school science Hydroponics Horticulture class uses it everyday. Students grow a hydroponic garden indoors and a traditional garden outdoors and keep a detailed field guide on how quick plants grow and the variables that affect growth.

In her Scientific Issues in the Developing World class, students discussed how to adequately feed and water the world’s population of seven billion people.

“We looked at the different types of gardening that is really intensive gardening, and this was one of the examples,” Metzler said.

A hydroponic garden can grow a lot more plants in a lot less space. Outside, 16 plants can fit into four square feet. Inside, 200 plants can fit into Metzler’s 8-foot-by-12-foot garden.

And with grow lights on all day and night, plants can grow fast.

“These plants are probably growing three times faster than normal,” Metzler said. “In here, you get to see the growth. If (students) have a three-day break or after spring break, they come in and the plants have quadrupled in size. Whereas the ones outside got a little bigger.”

The speed also allows students to see the life cycle of a plant in detail, she added.

Eighth-grader Avery Sommers said the hydroponic garden has made him more interested in gardening and was most surprised by “all the plants in such a tiny space.”

“It was really cool,” said seventh-grader Mary Logan Grier about gardening with hydroponics. “I had seen it walking by in sixth grade, (and remember thinking) what is that? Now I know what it is and how it works … I like how hands-on it is, and we get to see the before and after.”