What do you do with tons of broken glass? Grow tomatoes.

Mmmm. Nothing like biting into a fresh tomato. Be mindful of the broken glass, though.

Samuel Garrett McKee, a senior in forestry at the University of Missouri College of Agriculture, Food and Natural Resources, is finishing an undergraduate research project that combines recycling with something good on a salad.

When he heard how much waste glass the City of Columbia has to dispose of each year, he saw an opportunity to use this material, which ordinarily goes into a landfill, as a medium for growing hydroponic tomatoes. He harvested his first tomatoes using this process on Dec. 13, 2008.

"There hasn't been a lot of research done on growing plants in crushed glass, at least I could not find any in the literature," McKee said. "Crushed glass is normally used as an aggregate in asphalt, but that is about the extent of the current market for it. There are tons and tons of it available, it just needs a market."

Hydroponics, from the Greek words for water and labor, is a method of growing plants without soil. Hydroponically-grown plants usually have their roots in a mineral nutrient solution, or in an inert medium such as perlite, gravel or mineral wool.

"My research discovered that crushed glass will work as a base for growing vegetables hydroponically," McKee said. "I have not analyzed all the data, but my test plots produced tomatoes at roughly the same rate as two other commercially available hydroponic growth mediums, perlite and hydroton."

Of the materials being recycled today, glass is still one of the most difficult to reuse. One major problem is the separation of clear and colored glass. When colored glass is mixed together, the result is an undesirable greenish-brown color.

The glass component in municipal waste is usually made up of bottles, broken glassware, light bulbs and other items. A study by the Missouri Recycling Association indicates that about 5.4 percent of the state's waste stream that ends up in landfills is mixed glass.

McKee's hometown is DeSoto, Mo. He plans to work in conservation. He has a dual major in forestry/fisheries and wildlife with a soil science minor.

"The glass currently is very low cost because there is so much available," he said. "The other two growth mediums I tested it against cost much more. Also, since glass is inert, I believe it can be reused indefinitely whereas the store bought growth mediums are porous and will fill with salts over time, making eventually them unusable for growing plants. By providing the glass with a new market, recycling glass will become that much more profitable."

"Recycling is a wise use of natural resources and I am happy to contribute to its success."

Posted Dec. 29, 2008
Story by: Randy Mertens.
Photo credit: Sam McKee.