A flower pot for young seeds made out of newspaper.

Chicago Tribune / Bill Hogan Bill Hogan

CHICAGO — In the garage, shed or basement of nearly every gardener, you will find stacks of plastic pots. Then there are mulch bags, pesticide and fertilizer bottles, flat trays from six-packs of annuals. We think of our gardening as greening the world, but it generates a lot of plastic garbage.

Gardeners may not realize how much. Nursery pots, flats and cell packs use up to 320 million pounds of plastic a year, according to a 2004 estimate from the Penn State University College of Agricultural Sciences in University Park, Pa.

Where does it all go? We may reuse some pots or crumple some cell packs in the bottom of containers to save potting mix. But in the end, most of the plastic from our gardens goes to landfills or hazardous waste incinerators.

“A very small percentage of agricultural and gardening plastics are recycled,” said Lois Levitan of the Environmental Risk Assessment Program at Cornell University in Ithaca, N.Y.

Ultimately, it’s up to gardeners to reduce those piles of plastic by buying less, encouraging the horticulture industry to find better methods of packaging and pressing for more recycling.

Nationwide, only 3.9 percent of the 26.7 million tons of plastic generated in the U.S. was recycled in 2003, according to the U.S. Environmental Protection Agency. And most of that was soda, water and milk bottles. Little garden garbage makes the cut.

For any commodity to be recycled, it has to be available in a large enough quantity and a steady supply to be worthwhile for manufacturers and their suppliers. Milk jugs and water bottles are fairly standardized, which makes it easy to gather a lot of those plastics through recycling programs.

But plant pots are as varied as flowers, because different growers use them in different ways for different stages of a plant’s life.

A petunia, grown from seed to be planted in the garden within a few months, doesn’t need much of a pot. It usually gets a flimsy six-pack made of polystyrene, said Marc Teffeau, director of research and regulatory affairs for the Horticultural Research Institute of the American Nursery and Landscape Association in Washington, D.C.

But a shrub, which will be in a pot for two or three years before it reaches salable size, needs something much more substantial. It likely gets a container made of high-density polyethylene.

Every grower uses a different assortment of pots to suit its own products, growing methods and marketing strategies. That makes it hard to assemble enough of any single kind of plastic from horticulture to be worth recycling.

Much garden packaging doesn’t even carry a recycling code — the number in a triangle that is used to classify plastic for recycling. And even when it does and a gardener puts it in the recycling bin, the small quantities collected of each kind probably mean that plastic will be part of the “residual” that leaves the recycling center for a landfill. Many recycling programs don’t take the No. 4, 5 and 6 type plastics used in most pots, or discard them because they have soil clinging to them.

Plastic has become ubiquitous for horticultural packaging because it is lightweight, easy to shape and cheap. But an increased green consciousness is putting some pressure on the horticulture industry to deal with the irony of a “green” business generating so much waste. Another factor: the rising price of oil, from which all plastic is made.

Home Depot recently has begun selling organically grown plants in biodegradable peat pots (at higher prices). There are research efforts under way on burning plastics for fuel. Some growers have started using biodegradable paper pots for small plants (though they still are held up by plastic holders). And there is a boom in research on “bioplastics” — made from plant or animal products, they are intended to be light and easy to shape like plastic but made from renewable resources and biodegradable. There even has been research on making biodegradable pots from cow manure.

Standardization to limit the sizes and plastics of pots would help recycling efforts, said Dave Bender, executive director of the Illinois Green Industry Association, a trade group of nurseries and garden centers. The group has a three-year plan to work on the issue, he said, but no results so far.

For those who do recycle garden plastic, it takes a serious extra effort.

The Chicago Botanic Garden saves up its surplus plastic pots to be shipped by the truckload to a Canadian firm for recycling, said Tim Johnson, director of horticulture.

The Missouri Botanical Garden in St. Louis operates the only large-scale program in the nation for gardeners to recycle pots. In 1998, when the program started, managers were astounded at the pile gardeners dumped in the parking lot: 80 feet long and 20 feet high, said Steven Cline, manager of the garden’s Kemper Center for Home Gardening.

Last year, the garden recycled 70,000 pounds of plastic, dropped off at the garden and participating nurseries. This year, they’re shooting for 100,000.

But since the market for recycled pots is so limited, the garden had to seek grants from government and horticulture businesses to buy its own $150,000 granulator machine to grind up the pots. It only takes polystyrene (No. 6), high-density polyethylene (No. 2) and polypropylene (No. 5). And the garden has had to go into the business of making plastic lumber to use the polyethylene and polypropylene.

Wouldn’t it be easier and cheaper for the horticulture industry to reuse existing pots? Returning the pots to growers would be a huge undertaking, especially with no standardization. And growers are afraid that disease-carrying bacteria or fungi — which can devastate a greenhouse business — could sneak through any cleaning process.

The Chicago Botanic Garden depends on volunteer labor to clean pots for reuse, Johnson said. The Chicago Park District gives many plastic pots from the Garfield Park Conservatory to Growing Power, a non-profit sustainable agriculture organization with farms in Chicago and Milwaukee.

But so far there is no easy solution for home gardeners.

Some nonprofits may take donated pots. Some, but not all, nurseries may take back their own pots as a gesture of goodwill. They won’t necessarily recycle or reuse them, though, and they are unlikely to take pots from plants bought anywhere else.

That leaves it up to gardeners: to be aware; to reduce the amount of plastic packaging we buy in the first place; to reuse what we already have; and what we can, recycle, — or ask garden businesses and municipalities to work harder to make recycling possible.