"Green" Greenhouses

A production greenhouse is about as unnatural an environment as you can get. The temperature is constant, it rains at precise intervals, and the greenery grows with an almost eerie symmetry. Wetlands, on the other hand, are filled with cattails, frogs, ducks, and reeds. They grow wild and free, and act as natural filters capable of cleansing the water flowing through them. Agricultural engineer Eileen Wheeler, horticulturist Berghage, and agricultural engineering graduate student Tawni Hoang are working on ways to incorporate the natural cleaning abilities of wetlands into the artificial environment of a greenhouse.

"Most large production greenhouses have recirculating irrigation systems to save labor costs, conserve water, and keep chemicals from entering water supplies," Wheeler explains. "Unfortunately, some nutrients and pesticides can slowly build up in the recirculating water. Eventually this buildup will harm plants or cause target pests to develop resistance to pesticides."

Greenhouse irrigation systems also produce wastewater laden with tremendous amounts of inorganic contaminants, such as salts and nitrates. The Environmental Protection Agency drinking water standard for nitrates is 10 parts per million. Greenhouse irrigation typically carries nitrate loads of 100 to 200 parts per million.

Constructed wetlands have been established outdoors to treat municipal, industrial, and agricultural wastewater, but those facilities need large amounts of land and surface area to function correctly. Berghage and Wheeler sought to construct an artificial wetland that not only would efficiently clean water, but also was small enough to take up a minimal amount of growing space in a production greenhouse. In a controlled greenhouse environment, the wetland can function near optimal levels year-round, avoiding any slowdown in the filtering process caused by cold or freezing temperatures outdoors. "Our goal was to build an inexpensive, low-maintenance system," Berghage says. "We want to be able to build it and then walk away, because greenhouse operators won't have time to tend these systems."

Hoang and Wheeler designed artificial wetlands in 50-gallon tanks filled with gravel. Half the wetlands were planted with common bulrushes and the rest remained unplanted. "Microbes in the wetlands can break down contaminants such as growth regulators and nitrogen into nitrates and ammonium, which are then used as nutrients for plants," Hoang explains. "Nitrogen dissipation in a wetland may proceed through several pathways, but the process of nitrate reduction to atmospheric nitrogen gas has gained the most attention in wetland studies."

To dissipate nitrogen in water, a chemical reaction is required, Wheeler explains. As water travels through the gravel and plant roots, a series of transformations alter the chemical structure of nitrogen. The final step, where nitrates change to nitrogen gas, requires the addition of a carbon source to feed the microbes responsible for changing nitrates into gas. "We found that adding carbon--I used table sugar--significantly reduces the time and size of the constructed wetland needed to remove the contaminants," Hoang says. The planted wetlands with carbon were able to reduce water with nitrate loads of 100 parts per million to 10 parts per million--the EPA standard--in just two days. Planted wetlands with no carbon additives took two weeks to reach acceptable levels. In contrast, the wetlands with neither plant material nor carbon additives reduced nitrogen to about 70 parts per million in 23 days, just a 30 percent reduction. "Planted wetlands do take up growing space in a greenhouse, but it's clear they filter important contaminants," Hoang says. "Greenhouse growers also might be able use filter plants with retail potential, such as aquatic plants."

As consumers seek out more and more varieties of plants to make their homes and businesses beautiful, they create a tremendous demand for another landscape product--mulch. In the past two decades, rising demand for mulch has changed how the substance is manufactured. In 1970, most mulch was created from tree bark, a residual product of the wood processing industry. Today, manufacturers add much more raw wood into the mix. "Companies are using slab wood from the first cuts on a log, whole trees from landscape clearing, recycled pallets, and lumber scraps," says plant pathologist Don Davis. "Mulches aren't stored for long periods, either. It's bagged and sold as fast as they can make it."

Hidden within these mountains of mulch lies a fungus that is intent on some explosive growth of its own. Called "artillery fungus" or "shotgun fungus," this organism favors wood-based mulch. The wood-rotting fungus appears as a small cream or orangish cup containing a black rounded spore mass. As the fungus matures, the cup containing the spores opens and blasts its spores into the air. "The fungus orients itself to face any light-colored structure, which is often a house or automobile," says plant scientist Larry Kuhns. "Once the spores are ejected, they can adhere to any surface in its range. On a house or a car, these spores will speckle the surface. Many homeowners think the damage is caused by insect excrement."

Kuhns and Davis are in the middle of a five-year research project to offer solutions to homeowners who have been bombarded by the fungal fusillade. Graduate assistant Beth Brantley is testing 30 different mulch types and blends to see which mulch products support the growth of the fungus. The researchers also are testing ways to remove the spores from surfaces as well as methods to deter its growth. "This fungus has been around for years--there were articles written on it in the 1920s," Davis says. "But in the last 5 to 10 years, the fungus has gone ballistic. It has a new surface to grow on, and it likes this one better." Kuhns and graduate student Kristen Akina started research on cleaning the spores in July, testing six commercial products designed to remove urban graffiti. They also are testing whether protective coatings will prevent the spores from sticking to metal and plastic siding.

"If you clean the spores off immediately, they're much easier to remove, but these things are tough to remove no matter what you do," Kuhns says. "Although the spores look like tar, they really are a water-based glue, and most oil-based solvents won't work on them." The next phase of the project focuses on composting mulch with substances containing organisms and bacteria that inhibit the growth of the fungus. Test compost piles have been prepared using sewage sludge, spent mushroom substrate (SMS), and composted yard waste. Early experiments indicate that selected strains of two microorganisms found in SMS, Bacillus subtilis and Trichoderma harzianum, will inhibit the growth of artillery fungus in laboratory conditions. "These organisms show potential as a solution, but in nature things aren't that simple," Davis explains. "If it works in the real world, then it becomes a win-win situation for Pennsylvania. The state's mushroom industry produces much more SMS than it can dispose of, and this might create another market for that material."

The search for new markets for plants, gardening services, and gardening material shows few signs of slowing down. All areas of the green industry are showing healthy economic growth, and some horticultural businesses have cultivated market niches that provide enviable profits. Penn State's extension staff and horticulture faculty have adapted well to this ever-changing business climate. The college has been able to design programs that mirror the needs of specific regions, be it the populous suburbs around Philadelphia or the rural expanses of northern-tier counties. "We educate professionals in horticultural industries and we educate their clientele," says Rick Johnson. "By educating the consumer, you create a demand for better products and services. That, in turn, helps build the industry professionally. We're serving the green industry through the front door and through the back door. It's a perfect picture of how outreach is supposed to work."

Faculty and extension staff referenced in this article are: Robert Berghage, assistant professor of horticulture; Steven Bogash, extension agent in Blair County; Gregory Burns, extension director in Cameron and Elk Counties; Donald Davis, professor of plant pathology; Gregory Hoover,extension entomologist in entomology; Rick Johnson, extension agent in Delaware County; Larry Kuhns, professor of ornamental horticulture; Michael Masiuk, extension agent in Allegheny County; Gary Moorman, professor of plant pathology; James Sellmer, assistant professor of ornamental horticulture; David Suchanic, extension agent in Montgomery County; Emelie Swackhamer, extension agent in Lehigh County; Eileen Wheeler, assistant professor of agricultural engineering; and Dennis Wolnick, associate professor of floriculture. Many of the extension agents listed here have multiple-county areas of responsibility beyond their home county. Research is funded by the Pennsylvania Department of Agriculture, The Exxon Foundation, and SEPRO, Inc. The Southeastern Pennsylvania IPM Research Group is on the Web at: http://www.sepaipm.cas.psu.edu.