Discarded glass bottles probably don’t come to mind when you think about ingredients for a soil amendment. Growstone, a New Mexico-based company, has found a way to turn this waste into a sustainable product suitable for gardens and other uses.
Founders Andrew Ungerleider and Gay Dillingham, self-described “eco-preneurs,” began investigating sustainable business practices after witnessing destructive strip mining for pumice taking place in New Mexico. Ungerleider realized the only way to combat this was to find a better alternative to pumice. He developed a new method for recycling glass into a super-fine powder that could be used to manufacture products for cleaning and sanding.
Small particles of this rigid yet porous material turned out to be suitable for horticulture. These “Growstones” improved water retention and aeration when added to standard growing media. Researchers at
Stone crafting
The glass used for Growstones goes through a dramatic transformation during the manufacturing process. Bottles are first crushed into small pieces and then further ground into an extremely soft powder. Natural foaming agents and additives help create the specific formula needed to produce the stones.
The material is then blended and poured into large molds, which are placed in a big kiln. The formula rises as it bakes, creating a rigid foam. Bubbles are created as air releases in the heating process. The bubbles take a twisting path as they escape, creating a network of cells in the material.
Once the baking process is complete, the blocks of material are carefully cooled. The “cakes” are then ground into tiny bits to produce Growstones. Stones for hydroponic uses are 1/2 to 1 inch in diameter. Particles for soil amendments are smaller, usually 1/16 to 7/16 inch. The finished product comes in several colors, many of which blend into the soil.
“Garden centers have been very excited that we can manufacture different colors,” said Chris Higgins, Growstone vice president of agriculture. “They like when you water that you don’t have white stuff appearing. Homeowners perceive that perlite floats to the top and our product stays where it needs to be.”
Garden benefits
Homeowners can use Growstone soil amendment in containers and gardens. When combined with a potting mix, Growstones helps retain moisture and improve drainage. The stones can be tilled into flower and garden beds to reduce water requirements. Growstones can also be used with organic mulch around trees to hold in moisture and limit weed growth.
Gardeners also benefit from the long lasting effects of the product.
“It’s not really going to break down in the soil rapidly,” Higgins said. “You’ll be able to use it over again. The particle size is large enough that it will still be able to produce drainage and water retention benefits. Eventually you can break it down enough where it will basically become sand again.”
Increased availability
More garden retailers will be able to get their hands on Growstones starting this month. A big launch at the National Hardware Show, May 6-8, helped generate a wider audience for the product. Initial distribution will be in Southwestern states, but the company plans to expand its reach as more distributors are brought on board.
Higgins said additional items using Growstone’s recycled glass formula will be making their way into the market. The company plans to offer a garden tool cleaner, an after-gardening hand cleaner and spa treatment and GrillStone, an abrasive product used to clean barbecues.
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For more: Growstone, (469) 532-2261; http://growstone.com.
May 2008