Recycled glass has been used to grow plants to make salsa.
Coriander, bell pepper, and jalapeno were cultivated in glass from pulverized beer and pop bottles by American scientists.
The pilot study found that partially substituting soil in a planter with recycled glass shards speeds up plant development and reduces unwanted fungal growth.
When nanomaterial scientist Dr. Julie Vanegas joined the faculty at The University of Texas Rio Grande Valley, she was paired with faculty mentor Professor Teresa Patricia Feria Arroyo, an ecologist who works on solving problems related to food security and sustainability.
During their early conversations, Dr. Vanegas mentioned that she’d been assessing recycled glass particles for coastal restoration projects, such as growing willow trees.
Feria wondered if glass could also be used for growing produce.
Together, they developed experiments for growing foods that people are familiar with, mature quickly, and can be cultivated in container and backyard gardens – the ingredients for pico de gallo: a popular type of salsa.
“We’re trying to reduce landfill waste at the same time as growing edible vegetables,” said Andrea Quezada, a chemistry graduate student in the Nanoworld Vanegas lab.
“If this is viable, then we might be able to introduce glass-based soils into agricultural practices for people here in the Rio Grande Valley and across the country.”
For their experiments, the research team gathers recycled glass particles from a company that diverts bottles from landfills, crushes them into particles, and tumbles the pieces to round off the edges.
The team says the final product is smooth enough that people can handle the glass bits without getting cut, and plant roots can grow around the glass pieces without being harmed.
In initial tests, the researchers assessed the soil-like qualities, such as compaction and water retention, of three different-sized glass fragments.
The team found that a size similar to coarse sand grains had characteristics, such as allowing oxygen to reach the roots and maintaining sufficient moisture levels, that could be ideal for plant cultivation.
Now, the team is evaluating the recyclable glass material as a viable substitute for soil.
In a greenhouse on campus, they’re growing cilantro, bell pepper, and jalapeño plants in a variety of pots containing anywhere from 100% commercial potting soil to 100% recycled glass.
Pots with more soil have higher levels of nutrients required for plant growth, including nitrogen, phosphorus, and potassium, compared to those with more glass.
But there’s little difference in pH level among the pots, which the researchers say is a “promising” result because plants thrive in a narrow soil pH range.
Early results suggest that the plants grown in recyclable glass have faster growth rates and retain more water compared to those grown in 100% traditional soil.
“A weight ratio of more than 50% of glass particles to soil appears best for plant growth compared to the other mixtures we tested,” said Dr. Vanegas.
The researchers are waiting until harvest time to confirm what soil mixture produces the highest yields – and tastiest produce.
Pots with 100% potting soil developed a fungus that stunted plant growth.
Feria believes the fungus may impact nutrient uptake by the roots.
But the pots that included any amount of recyclable glass didn’t have any fungal growth. The researchers are collecting data to determine why that might be.
These results are particularly promising because the study was done without fertilizers, pesticides, or fungicides.
Quezada noted, from her experience working in agriculture, that a lot of the chemicals applied to the land impact people such as her family members who work or live around farming communities.
She added: “I think it’s really important to try to minimize the usage of any chemicals that can negatively affect our health.
“If we are able to reduce them, and help the community by collecting recyclables, then we can give people a better quality of life.”
The findings were presented at a meeting of the American Chemical Society in Denver, Colorado.
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