Amelia Argyropoulos

Amelia Argyropoulos researched whether plants grow better with mulch added to the soil.

Adding mulch to your garden will keep back weeds and keep soil cooler even on the hottest days. But does mulch help plants grow better?

Amelia Argyropoulos of Lancaster looked into that question. She compared plants growing in commercial shredded wood mulch, homemade shredded paper mulch and no mulch. Her research won second place in the junior plant science division in the 2021 North Museum Science and Engineering Fair.

Amelia, 12, first saw the mulch topic online at Sacred Heart School, where she’s now a rising eighth grader. She wanted to learn more.

“A lot of people decide to use store-bought mulch instead of different types of mulch,” she says. “I wanted to do a project on it to be able to determine if it’s really better.”

Many mulches

Mulch is not just shredded wood. It’s any ground cover, including living plants like lemon verbena or crimson clover; organic material like bark chips or shredded leaves; and synthetic materials like rocks or landscape fabric. Gardeners use mulch for a few reasons, says Diane Diffenderfer, master gardener coordinator and horticultural educator with Penn State Extension’s Wayne County office.

“One is to conserve soil moisture, reduce weed pressure and hopefully add organic matter back into the soil as it decomposes,” Diffenderfer says.

For Amelia’s research, she narrowed down her mulches to a shredded wood mulch and a mulch made at home from shredded paper.

Seeing so much information online about commercially available mulch, Amelia expected that type of mulch to perform best, she wrote in her hypothesis.

She planted daffodil bulbs in soil with one inch of mulch on top. Her control group had no mulch. Amelia placed these under a grow light in the basement of her Lancaster city home, where she lives with her parents, Peter and Beata, and brother, Bartek.

She first focused on which mulch retained the most moisture. Too much moisture is not always better for plants, as she learned in the first week of the experiment. After adjusting the amount of water, she shifted to measure the growth of the plant.

Amelia measured plant growth by weighing the plant pots and their contents. Some of the bulbs had already sprouted before planting so she didn’t want to compare plant heights.

Mulch experiment

Amelia’s findings

After a month, she looked at the data and made a conclusion.

“The homemade mulch ended up retaining the most moisture and helping grow the plants the most,” she says.

The wood mulch came in second. The control group grew the least, which did not come as a surprise.

“I knew one of the two mulches would obviously win the experiment,” Amelia says. “I didn’t think the control group was ever going to have a chance at it.”

After the experiment ended in January, the plants were taken outside, but most didn’t last much longer.

Amelia’s advice for gardeners: use homemade paper mulch.

“It’s more effective, and it costs less money,” she says.

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