January 19, 2010 | General

Composting Integral To Public Garden

January 2010 BioCycle cover, Compost use in high-end horticultureBioCycle January 2010, Vol. 51, No. 1
Longwood Gardens in Pennsylvania incorporates composting into its horticultural operations as well as its research and educational programs.
Clare Wagner and Casey Sclar

AT Longwood Gardens, a 1,077-acre display garden located in Kennett Square, Pennsylvania, composting has gone beyond just being a way to recycle organics. Not only does Longwood produce high quality compost for use in its horticultural and agricultural operations, its composting facility also serves as a resource for research and education, and a model for other entities looking to establish farm-scale composting.
Longwood Gardens is a 501(c)3 nonprofit organization with the mission of inspiring people through excellence in garden design, horticulture, education and the arts. Environmental stewardship is an essential part of Longwood’s Strategic Vision, and a diverse range of sustainability initiatives have been undertaken. While the composting facility is essential, other projects include an on-site recycling center, a waste-water treatment plant, soils recycling/conservation, and programs directed toward renewable energy sources and innovative land stewardship.
Longwood Gardens, Pennsylvania
The Longwood property is a former Quaker arboretum and DuPont estate with roots in agriculture. The composting operation is located in a nonpublic area of the property that includes a facility for soil mix processing and soils recycling (all spent growing media is screened for reuse as a topsoil amendment and mulch feedstock), as well as agricultural fields. Composting at Longwood began in the 1980s but was expanded and refined beginning in 2002. In 2006, the six acres devoted to composting received an On-Farm Composting Permit from the Pennsylvania Department of Environmental Protection.

The organics recycling operation produces leaf mulch, hardwood mulch and two kinds of compost. Some raw by-products from mulch production include wood chips and ground fines. The mulches are produced from a combination of on-site and local community collections/drop-offs. Feedstocks for the hardwood mulch include twigs, branches, pallets, fiber pots and planting stakes, while leaf mulch is made solely from leaves.
Leaves are processed using a front-end loader, tractor and a New Holland manure spreader; the product is aged throughout the winter season. Longwood processes about 1,000 cubic yards of leaves each year, resulting in about 500 yards of finished leaf mulch. It is used mainly for aesthetic purposes in annual beds, because of its somewhat high (~7.5) pH levels. As the use of Longwood’s finished compost has increased, leaf mold use is on the decline.
A Peterson horizontal grinder is rented twice a year to shred the woody material for hardwood mulch. It is ground to 6 inches, screened using a McCloskey trommel, then reground to 2 inches. Fines from screening (“ground fines”) are used as a compost feedstock or soil amendment on the adjacent farm fields. The hardwood mulch is aged for 6 months prior to use. The site collects about 5,000 yards of brush and debris each year to produce about 2,000 yards of finished mulch, although this throughput increases annually. Currently, all the hardwood mulch is used in the garden on tree rings, planting beds, and on paths for cultural and aesthetic purposes.
Longwood Gardens composting process
Longwood’s composting facility accepts several feedstocks: horse manure gathered from local farms, wood chips retrieved from on site and the community, food waste and horticultural residues from on-site operations (“greens”) and the ground fines from mulch production. Both pre and postconsumer food waste, including compostable dishware and containers, are collected from The Terrace, Longwood’s restaurant. Cross-stream contamination is addressed, with attention to better collection bins, signage and restaurant staff training.
Feedstocks are collected at the composting site and combined by weight in a Kuhn Knight 5156 Vertical Mixer/grinder. Two recipes are used. The first is a 2:2:1 mix with two parts manure to two parts wood chips to one part ground fines. This is traditionally used for potting and bedding mixes. The second is a 1:1:1 mix with one part greens to one part manure to one part wood chips, which is utilized for topdressing agricultural fields, turfgrass areas and flower beds.
Once the feedstocks are batch mixed based on weight, windrows are created with the mixer. For a period of 10 to 12 weeks, the piles are closely monitored and turned using a Sandberger [Autrusa] ST-10 PTO windrow turner, based on daily temperature readings with Reotemp thermometers and oxygen readings if needed. Solvita maturity tests, readings of pH and EC values, and the results of seed germination trials are used to determine compost batch maturity and quality. Periodic microbiological diversity testing is performed by an outside laboratory. In 2009, about 2,500 cubic yards of compost were made from approximately 7,000 cy of feedstocks.
Compost quality has greatly improved as the equipment fleet and monitoring techniques have been developed and fine-tuned. While traditional uses still apply, new applications include increased compost use in potting mixes for greenhouse and outdoor containers as a peat moss replacement. The 2009 growing season marked the first use of the 1:1:1 recipe as a peat replacement in pots, including decorative containers at The Terrace restaurant patio. In addition, more formal research is being completed on peat replacement with compost. So far, the results indicate that about 75 percent peat replacement by volume is easily achievable for many crops with no quality loss, and there are no soluble salts concerns past the first two watering cycles – where having a slight fertilizer charge actually serves as a benefit to transplant establishment.
Longwood has taken advantage of research opportunities at the site in other ways. Studies have been completed relating to use of compost and compost teas in pest management. Another major research undertaking is the study of biodegradable and compostable containers from greenhouse production through in-ground (post-planting) performance or windrow composting. Results of this show little variation in plant performance, and none of the compostable pots (including rice hull pots and wood fiber containers) remain through a typical 8- to 12-week composting cycle.
Compost mixing
In January 2009, Longwood engaged in an economic analysis of its composting operation. The goal was to perform a thorough operational cost/benefit analysis of the farm-scale composting facility. The components analyzed include feedstocks, products, equipment and labor. Feedstock amounts were used to determine diverted landfill costs, while product amounts and values provided diverted purchasing cost data. Equipment and labor represented the incurred operational costs.
Data collection was central to the analysis and involved developing material and labor tracking techniques at the composting site. For equipment tracking, Longwood already utilized Dossier, a software program for fleet equipment management. Labor tracking was completed using weekly task-based hour worksheets for each employee. Materials tracking was also completed using weekly sheets, including amounts and the source and destination of both feedstocks and products. The data is compiled into an integrated Excel workbook. Purchasing and equipment costs are only entered once annually, whereas material and labor cost data are updated monthly.
The workbook calculates information for the data year-to-date (such as employee hour totals and specific product or feedstock totals) and extrapolates to make estimates to determine annual bottom-line costs for operating the facility. While 2009 was the first year for the analysis to be completed with a full year of data, the tool has already been used to examine ways to make the operation more economically sustainable. For example, it showed that use of a horizontal grinder as opposed to a tub grinder could reduce contracted equipment costs by almost $16,000 per year. Further analysis looking into the amount of brush deposited by off-site contractors vs. on-site personnel was higher than initially thought (1,000+ yards per year as opposed to an estimate of 250 yards), which lends justification to charging a tipping fee for this material when balanced with production costs.
The workbook also provides a tool of year-to-date and annual estimates for all material and labor data, which is valuable in interpreting and maintaining the site. Table 1 illustrates this information. Labor is calculated by percentage of time to make compost, mulch and leaf mold. While the workbook allows for more precise labor calculations, a standard labor rate of $25/hour was used in Table 1. This is not an actual value, and would vary facility-to-facility depending on several factors. Longwood plans to share the basic outline of the economic analysis with other operations to assist them in creating sustainable business plans.

Longwood Gardens provides details about its sustainability initiatives on its website ( as well as through displays at the garden. Recently, it began a visitors program called “Meet the Machine,” where a display on Longwood composting is paired with bringing a machine, such as the compost turner and tractor, into the garden for visitors to see and learn about. Behind-the-scenes tours of the facility are given to garden employees, students and professionals. The Longwood composting program has also been showcased in lectures and symposia, and was spotlighted as an on-site demonstration garden at a 2008 United States Botanic Garden sustainability display in Washington, D.C.
Longwood’s example shows that a composting facility linked to an institution such as a public garden can have many values. Understanding of the monetary value has been realized through the creation and use of tools to track the bottom line costs of running a facility. Besides the financial analysis, there is an additional environmental and community benefit of providing a composting site for many local operations, and diverting waste from the landfill. Creative interpretation and in-depth research on compost use are communicated to the public, furthering Longwood Gardens’ mission of inspiring people through excellence and leadership.

Clare Wagner has a BS in Agroecology from Penn State, where her thesis focused on the economic analysis in this article. She is now the Environmental Sustainability Intern at the Royal Botanical Gardens of Canada. Casey Sclar leads Longwood’s Plant Health Care Division, which oversees soil and compost operations and stewards 700+ acres of natural areas and farm lands. He has over 20 years of horticulture work experience, with a BS in horticulture from California Polytechnic State, S.L.O., as well as an MS and PhD in entomology from Colorado State.

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