November 24, 2008 | General

Compost In The Rain Garden Mix

BioCycle November 2008, Vol. 49, No. 11, p. 34
Nature reserve, conservation district and composting facility team up to treat storm water at Visitor’s Center.
Molly Farrell Tucker

OLD Woman Creek Reserve, located on the south-central shore of Lake Erie, is the smallest and only freshwater estuary reserve in the National Estuarine Research System. The 571-acre federal and state nature reserve in Huron, Ohio has freshwater marshes, swamp forests, a barrier beach, upland forest, estuarine waters and tributary streams. Its Visitor Center features natural history exhibits, a freshwater aquarium, weather station, a bird viewing window and nature art exhibits.
Rain events were causing flooding and washouts at the Reserve’s Visitor Center. Barnes Nursery, Inc. in Huron and the Old Woman Creek Reserve (OWCR) teamed up with the Erie Soil and Water Conservation District (ESWCD) in June 2008 to install a rain garden at the Visitor’s Center to manage the storm water. This project was part of a new local “watershed approach” initiative, begun in 2008 by the Firelands Coastal Tributaries Watershed Program to educate homeowners in Erie and Huron Counties on how to reduce storm water pollution on their own property.
Barnes Nursery operates a composting facility that processes 20,000 tons of yard trimmings and food, agricultural and industrial residuals annually. The nursery also provides full service landscaping, has two garden centers and sells over 125 varieties of trees and shrubs. ESWCD provides services to urban and agricultural land users, including survey and design of grassed waterways, erosion control structures, surface and subsurface drainage and watershed planning and management.
“We were dealing not just with roof runoff from the Visitor Center but also runoff from the center’s parking lot,” says Bre Hohman, watershed coordinator for ESWCD. The parking lot at Old Woman Creek slopes towards the center, creating a ponding effect on the walkway. “Visitors to the Reserve would have to walk through the ponding water when coming into the building,” she explains. There also were washouts in an area along the side of the parking lot. “Rain would hit the parking lot and run really fast off the edge onto a grassy area,” says Sharon Barnes of Barnes Nursery. “It turned into an ugly spot that would pond and hold water all the time. It became a mess.”
Hohman’s plan was to create a rain garden in the grassy area, improve the infiltration rate of the soil and install mostly native plants in the garden. “There were no rain garden demonstration sites in the Huron area and OWCR wanted to have one as part of its educational program,” she says. Hohman designed the rain garden to be approximately 1,000 square feet in size. (By comparison, most residential rain gardens are 100 to 300 square feet.) “The awning located over the patio area flows directly into the rain garden and everything else is parking lot runoff,” she explains. “The rain garden had to handle both types of runoff, so this required a larger rain garden design.”
Hohman adds that rain gardens generally are designed for a one-inch rain event, but the Huron area is subject to frequent storms of greater than one inch. “If the garden were too small, the depth of the water could potentially kill off the plants,” she explains. “If the garden were too large, it would dry out, resulting in more maintenance.”
To calculate the approximate depth of the rain garden, a percolation test was performed to see how fast the soil drew down water. Three holes, each about the size of a coffee can, were dug in the grassy area where the rain garden was to be installed. The holes were filled with water and measurements were taken every 30 minutes for four hours. “The water should go down one inch per hour,” says Barnes. “If not, additional site preparation is needed.”
Soil was tested for nutrients and textural makeup (the ratio of sand-silt-clay). Amendments, including sand and compost, are frequently added to soil in rain gardens to manipulate how quickly rainwater percolates into the soil. “The soil at OWCR is pretty good, but we did find some heavy clay,” says Hohman. “If there is a lot of clay, the water will sit on the surface and burn out the plants.” There was also compaction because heavy construction equipment had run over the soil in the rain garden area when the Visitor Center was built. “We needed to loosen the soil and add rough organic material,” she adds. “We could have added sand, but if the soil is too sandy it will percolate very fast, which means the rain garden might have to be watered between storm events. The organic material helps retain water between the layers between storm events.”
Barnes Nursery had developed several compost mixes and made a custom mix for the OWCR rain garden. “Sharon Barnes has really been innovative in developing compost products for rain gardens and roof gardens in our area,” says Hohman. “The compost we used for Old Woman Creek was a coarser leaf material that loosened up the soil to increase the infiltration of rainwater, and gave the plants a better chance to take root.”
Adds Barnes: “Compost is a major part of a rain garden soil mixture. The specifications are usually one-third sand, one-third compost and one-third sandy loam topsoil, but there are different specifications for different projects that take into consideration what is already there and what is being removed.”
For the Old Woman Creek project, the rain garden soil specifications were 40 percent compost, 30 percent sandy loam topsoil and 30 percent sand. Barnes Nursery provided a special mulch blend for the finished garden made up of a 50-50 mixture of hardwood mulch and leaf humus, along with some of the plants. Because of the large size of the rain garden, a backhoe was used to excavate the existing topsoil. Soil was excavated to a depth of 10 to 12 inches, the subsurface was roughed up, and approximately 4 inches of the rain garden mix was applied. The rain garden was raised an additional 4 to 6 inches with some of the excavated soil amended with compost. After the planting was completed, 3 inches of mulch was applied.
The rain garden was sited 12 feet away from the Visitors Center building. A covered patio area runs 10 feet from the building, followed by 12-inch patio pavers and then river rock that acts as a French drain. Because the parking lot runs along one entire side of the rain garden, there are several points of entry for rainwater to flow into the garden. “We were concerned that water would concentrate in one area of the rain garden and cause erosion and push the soil and mulch around,” says Hohman.
Frank Lopez, manager of the Old Woman Creek National Estuarine Research Reserve and State Nature Preserve, devised the French drain solution – 3- to 4-inch sized river rock to help evenly spread rainwater entering the garden and reduce velocity of the flow. The parking lot side of the garden was lined with the rock to a depth of six inches and a width of one foot. “The river rock also makes a great transition from the hardscape of the parking lot to the landscape of the rain garden,” notes Hohman.
The rain garden lowers the ground elevation, adds Barnes, “allowing the water to naturally run off the parking lot and walkway and be retained in the garden.” The rain garden was designed to slope away from the building and parking lot, and to overflow into an open swale located away from the building to prevent flooding in a 100-year storm event.
The rain garden contains mostly native plants, with the exception of a few horticultural varieties of a native species. The plants include compact cranberry, witch hazel, coreopsis, sedum, swamp milkweed, butterfly weed, Jacobs ladder, prairie drop seed, marsh blazing star, coneflower, blue flag iris, blue joint grass, bottle brush grass and little blue stem. Some of the garden and native plants were purchased from Barnes Nursery. OWCR staff also harvested and transplanted some native plants growing in the Reserve.
“Native plants are generally hardier, have better and deeper root systems, require less maintenance and attract more wildlife,” says Barnes. “The pressures on wildlife are so great now with all the suburbs we have. If we start substituting native plants for some of the others in our home gardens, it will bring back butterflies, bees and other beneficial insects that don’t bother with the very pretty plants that have replaced native plants.”
One of the goals, says Lopez, was to be a demonstration site for homeowners. “The rain garden was a method that can be implemented by our visitors on their own land, which will have a positive effect on streams and watersheds.” Adds Barnes: “Research shows that when housing developments effectively install rain gardens there is 90 percent less runoff compared to neighboring developments, square foot for square foot.”
To ensure that visitors could fully experience the rain garden, a path of stone pavers was added through the center and plants were tagged to reference their species names and whether they are locally harvested or purchased from a nursery. “We also put up signage explaining the uses, benefits and design specifications of the rain garden,” says Hohman. “Others don’t have to go to the extreme we did, but it is a demonstration site and we wanted it to work well. We followed the book closely, going through the calculations for the slope and layout.”
Five workshops have been conducted on rain gardens as part of the Firelands Coastal Tributaries Watershed Program, including two during construction of the OWCR garden. “Barnes Nursery will be partnering with ESWCD to provide additional trainings on rain garden designs with demonstrations like the Old Woman Creek rain garden,” says Barnes. “People are looking for good, sustainable, alternative solutions for water problems, and the local nursery needs to be part of that solution to stay relevant.”
There were a few setbacks after the rain garden was installed. “A few placements of plants didn’t do as well as we hoped, either because they got too much rain or didn’t transplant well,” says Hohman. “They were harvested on site and the root systems could have been damaged.” She adds that “rain gardens are not their prettiest the first year you put them in. They have bigger blooms the second year.”
During a typical rain event, e.g., a half-hour downpour, the rain garden fills up within 15 minutes and is completely dry eight hours later. Weather extremes have been a problem. “When we first put in the rain garden, it was a pretty wet June,” explains Hohman. “We kept getting hit with more and more rainstorms, so it would take one full day to saturate to the surface.” Drought-like conditions later in the summer of 2008 required watering the garden as needed to better establish plant life, adds Barnes. “We expect that watering needs will reduce as the plants’ root systems fully develop.”
Weeding also has been necessary. “The flowers and grasses were spaced apart to allow for future growth and unfortunately this leaves room open for weeds,” Hohman adds. “Weeding will be a part of regular maintenance for the first few years until the garden plants have grown together.”
All in all, the Old Woman Creek rain garden has been a success. “After the garden’s installation, many visitors have inquired about plant selection, placement and the process of construction, so the garden is working well as a management practice and as a learning device,” notes Lopez. “It is attractive and very effective at reducing storm water flow from our Visitor Center that would impact the estuary.”
Molly Farrell Tucker is a Contributing Editor to BioCycle.
Sidebar p. 36
BARNES Nursery, which supplied the compost and blended soil for the Old Woman Creek Reserve Visitor’s Center rain garden, has been making and marketing compost for many years. Almost all of the compost is screened to a half-inch with a trommel. Further refinement is done with other equipment and/or a second screening. “We have really channeled most marketing to use compost screened to a half-inch,” says Sharon Barnes. “We don’t try to sell to golf courses, for example, because it is too expensive to screen a yard waste compost to the 3/8-inch size they need for topdressing.”
When making the soil for the rain garden, Barnes Nursery started with the half-inch screened compost. The soil was screened, and then the materials for the rain garden mix – compost, soil and sand – were all screened together to meet the specification. Recently, the nursery received a grant to purchase an Extec E-7 vibratory deck screen and a bagging unit from Rotochopper. Barnes explains that the Extec, which is used primarily in the soil and aggregates industries, is effective at removing rocks from the soils, as well as the foundry sand that it recently began receiving. “Over the years, we found that we needed a better soil screener to get real production in making blends,” she says. “We rented a vibratory screen for several months a year, and our operators in the production yard hated when we had to send it back. We had the opportunity, using market development grant funds from the Ohio Department of Natural Resources, to purchase the deck screen, along with the bagger.”
The CreekSide Organic Material Processing Facility, owned and operated by the City of Hutchinson, Minnesota, processes 30,000 tons/year of grass, leaves and yard trimmings, producing about 25,000 cy/year of compost. Most of the finished material is screened and bagged. The CreekSide Soils line, about 50 percent of the operation’s sales, is dedicated to the high end user. “Those customers expect high quality in the bag, so we screen the compost in our McCloskey 733 trommel to 3/8-inch, and then run it over the bivi-Tec screen to refine it further,” says Doug Johnson, CreekSide’s manager. “The products sell for about $2/bag.”
The first panel of the McCloskey trommel has half-inch holes; the remaining part of the 33-foot screen has 3/8-inch holes. “Our biggest seller is topsoil, which is compost with about 10 percent sand,” notes Johnson. He recalls that when the facility first opened, they marketed the compost to a large nursery that was well known for products that Master gardeners use. “We were screening down to as small as 5 millimeters with the bivi-Tec and producing 40 to 50 cy/hour,” he says. “When we have demand for greater volumes, that is not enough productivity.” As they talked more to their end users, they learned that sometimes the product was too fine and water wouldn’t penetrate the material. “We found that a little bit bigger particle size was better suited for this market.”
Most recently, the CreekSide Organic Material Processing Facility purchased an Extec vibratory deck screen that can pulverize, mix and screen material “in one shot.” This is beneficial for the operation, which has started bagging a lower grade compost in higher quantities. “We can put 250 cy/hour through the new screen at 25 to 30 percent moisture content,” says Johnson. “With that kind of throughput, we can be more competitive to meet the big box store prices.”

Sign up