Landscape Performance Benefits
- Restored or improved soils on 120 acres. In one representative sample, soil testing showed a 300% increase in organic matter between 2010 and 2016.
- Manages the 1-inch, 24-hour rain event with a total treatment capacity of 49,000 cu ft in bioretention facilities, pervious pavement, and a cistern.
- Intercepts 50,300 cu ft of stormwater runoff annually in 9,026 newly-planted trees.
- Restored riparian habitat along 2.7 miles of streams. Over 20 native species were planted along streams including trees, shrubs, ferns, and emergent wetland species.
- Increased ecological integrity of plant communities as demonstrated by an adjusted Floristic Quality Index (FQI) score of 54, as compared an FQI score of 0 for a turf mix typically used in subdivisions similar to the site’s previous condition. An FQI above 35 is considered to be “natural area” quality.
- Sequesters an estimated 22.03 tons of atmospheric carbon annually in 9,026 newly-planted trees, with 234 tons of carbon stored in their biomass. 20 years after planting, these trees will sequester 36.8 tons per year.
- Diverts approximately 10.5 tons of organic food waste from landfills annually by composting and reusing it on-site. This saves an estimated $6,400 annually when compared to conventional waste management practices.
- Diverted an estimated 247,000 lbs of construction and demolition debris by reclaiming 95% of building materials from 20 former residential properties.
- Creates a sense of connection to the landscape, with 95% of 833 surveyed visitors saying they felt very or extremely engaged and 92% saying that they engaged with the Glenstone landscape more than they typically do at museums.
- Increases feelings of emotional well-being according to 88% of 832 surveyed visitors.
- Provides educational value and jobs for recent graduates through the guide program, currently employing 40 guides who are trained in sustainability, horticulture, and other landscape topics.
- Catalyzed the creation of one new bus route serving Glenstone visitors and staff as well as local residents. In 2019, over 6,000 visitors arrived at Glenstone on the bus.
- Impacts visitors early in their visit, according to 15% of 750 surveyed visitors who reported first feeling impacted by the landscape on entrance road, 22% at the parking lots, 7% at the Arrival Hall, and 47% on the walk from the Arrival Hall to the Pavilions.
- Helped to legitimize and advance a Montgomery County-wide policy restricting the use of chemical lawn pesticides, with the policy upheld by court ruling in May 2019.
- Saves an estimated $160,000 annually in reduced mowing and maintenance costs by converting 91 acres of conventionally managed turf to meadow, fescue, and seeded understory.
- Creates landscape-related jobs for 15 full-time employees who manage the site and offer interpretive programs in Glenstone’s Environmental Center. Glenstone Foundation employs approximately 150 people total.
At a Glance
PWP Landscape Architecture
Former Land Use
12100 Glen Road
Potomac, Maryland 20854
2016 (Phase 1); 2018 (Phase 2)
Glenstone is a contemporary art museum in Potomac, Maryland, that brings together art, architecture, and landscape. This multi-year project has transformed former residential properties into a contemplative, integrated experience of unique architecture, rolling topography, native meadows, and site-specific sculpture. Glenstone exists within a formerly agricultural rural landscape in the undulating topography of the Potomac River Valley. Over the last century, the area was transformed into an assemblage of 1- to 5-acre suburban residential plots that weakened the function and perception of the natural topography of the region. Over 15 years of design and implementation, more than a dozen suburban home sites were acquired, assembled, and transformed into Glenstone, which knits together 230 acres of formerly disparate, resource-intensive suburban lots into an ecologically and socially productive landscape experience through a multi-year master plan. Phase 1 of the project regraded, reforested, and created a sculpture walk through the original 150-acre estate. Phase 2 expanded the site to 230 acres, integrating a new museum building, parking groves, walking paths, sustainable meadows, and outdoor museum spaces. The design and implementation of the landscape in both phases emphasizes a systems approach to landscape maintenance, water management, reforestation, and meadow regeneration.
- In Phase 1 of construction, the Gallery museum building was completed along with its regraded and reforested landscape. Phase 2 included the construction of the 204,000-sf Pavilions museum building and large expanded landscape.
- As part of Phase 2, 1.8 miles of Potomac River tributaries were restored in partnership with Montgomery County.
- 12,760 ft of pedestrian pathways and trails throughout the property provide access within the site and connect it to the public Bridle Trail. A public bus line also has a stop at the site.
- 84 acres of turf lawns and pasture were converted into sustainable meadows planted with all native species, including little bluestem (Schizachyrium scoparium) and purpletop (Tridens flavus). The meadows are mowed once per year and do not require irrigation. More conventional turf areas near the Gallery and adjacent pond are made up of 85,968 sf of no-mow-sod turf blend consisting of a blend of radar chewings fescue, beacon hard fescue, and navigator creeping red fescue, which minimize mowing and water use.
- 9,200 new trees were planted on-site, including tulip poplar (Liriodendron tulipifera), Eastern redbud (Cercis canadensis), and American hornbeam (Carpinus caroliniana). 400 existing trees ranging in size from 5-inch to 30-inch caliper were moved, stored, and replanted onsite.
- 33,106 sf of green roof on the Pavilion building is planted with 32 species of native plants, including hair-awn muhly grass (Muhlenbergia capillaris), dwarf crested iris (Iris cristata ‘Powder Blue Giant’), and wild geranium (Geranium maculatum). 18 species were planted as plugs, and 14 were seeded.
- 99.5% of fill used to create the site’s undulating topography was generated from building excavation or regrading other portions of the site.
- During regrading, topsoil was stripped and stockpiled into a contiguous area that was overseeded with cover crops to enhance the soil’s fertility. 25,000 cu yds of site-harvested topsoil was used to blend engineered soils for the project.
- The heart of the Pavilions museum building expansion is a 16,000-sf aquatic garden, which provides year-round interest for visitors. The water court is maintained without the use of chemicals and acts as a biofiltration system for roof runoff. It was constructed using a modular system of fiberglass-reinforced panels to allow for varying water depths to accommodate different aquatic species’ growth requirements. The water garden is planted with 4,389 individual plants, representing nine native and adapted aquatic species, including blue flag iris (Iris versicolor), several varieties of water lily (Nymphaea), and pickerelweed (Pontederia cordata). The plants support a variety of native amphibians and insects, including: Northern green frog, Northern leopard frog, grey tree frog, giant black water beetle, and 15 species of dragonfly. Western mosquitofish is used for natural mosquito and pest control instead of chemicals.
- Three underground cisterns with a total capacity of 1,000,000 gallons capture and store rainwater that is used for irrigation.
- Runoff from the Gallery roof and the only two turf areas on-site (near the Gallery and the pond) is directed to the adjacent large pond, where it is filtered through a new stone wall on one side of the pond with a wetland edge on the other side. A dry stacked stone process was used to construct the wall so that it filters surface runoff and shifts during freeze-thaw cycles to protect against rupture and eliminate the need for resetting.
- Composting strategies are used throughout the site instead of chemical fertilizers. These include onsite compost tea and composting stations that produce natural fertilizer and soil amendments.
- During project development, a severe storm downed 750 trees on the site, providing an opportunity to mill site-salvaged oak for use as fence rails in 3,100 linear feet of a four-rail wood fence along the Glen Road frontage.
- Carderock stone is used throughout the property, which is quarried locally only 9 miles from the site.
- Outdoor sculptures were permanently installed on the site as distinct focal points of the landscape, including: Richard Serra’s Sylvester (2001) and Contour 290 (2004), Michael Heizer’s Compression Line, (1968/2016), Andy Goldsworthy’s Clay Houses (Boulder-Room-Holes) (2007), Jeff Koons’s Split-Rocker (2000), Tony Smith’s Smug (1973-2005), Ellsworth Kelly’s Untitled (2005), and Charles Ray’s Horse and rider (2014).
- Create a seamless integration of landscape, art, and architecture across the 230-acre site.
- Engage museum visitors in the landscape from the moment they arrive, facilitating their enjoyment of art and architecture in an integrated environment.
- Minimize water use and maintenance requirements by utilizing a systems approach to water management, reforestation, meadow regeneration, and landscape maintenance.
- Restore existing water bodies to filter runoff and improve habitat for a range of native plants and animals.
- Reintegrate the former subdivision site with the topography of the Potomac River Valley through regrading, reforestation, and stream restoration and convert impermeable and unsustainable suburban features to sustainable woodlands in keeping with the regional land morphology.
- Utilize all-organic management practices across the site.
Organic Landscape Management
Prior to 2010, the landscape at Glenstone was maintained by practicing Integrated Pest Management, an ecosystem based strategy that relies on monitoring and pest control practices to manage pests economically. This maintenance strategy included the use of synthetic chemicals in fertilizers, as well was the application of chemical pesticides when treatment of insects, weed, algae, and fungal diseases was necessary. Since 2010, Glenstone has worked closely with Paul Tukey, who is now Chief Sustainability Officer at Glenstone. Glenstone now uses only naturally derived fertilizers and pest control products in tandem with sustainable landscape management practices including: onsite compost production, application of compost tea, interplanting areas of turf with clover, and hand-pulling, flaming, tarping, and weed whacking to remove undesirable plants. Mosquitoes at the Water Court are managed by mosquito fish instead of chemical products.
Experimentation and testing of sustainable management methods has allowed Glenstone to determine the most successful maintenance techniques for the site. An example of this is the removal of Japanese stiltgrass (Microstegium vimineum), an exotic invasive. Comparative testing of different eradication methods including controlled burning, hand pulling, and weed whacking proved weed whacking to be the most effective at Japanese stiltgrass removal. 5 acres of Japenese stiltgrass were then effectively treated using weed whacking. The success of these organic landscape maintenance practices helped to legitimize and advance a county-wide policy restricting the use of chemical lawn pesticides. The policy was upheld by court ruling in May 2019.
- Over 40 acres of meadow restoration was originally going to be installed with live plants at a cost of $25,000 per acre. Working with Glenstone Foundation and a meadow consultant, the design team was able to recommend a primarily seed-based establishment process, resulting in a savings of $20,000 per acre.
- Originally proposed as standard asphalt (approximately $3.50 per sf), Glenstone Foundation elected to make the staff parking area using permeable asphalt. While the cost was higher ($5.55 per sf), the benefits derived from improving stormwater quality, promoting infiltration, mitigation of heat island effects, and increased aquifer recharge were considered a higher priority.
- Given the large scale and long-term timeline of developing Glenstone, sourcing plant material became a significant challenge over the course of the project. Working with both the Glenstone Foundation (the managing entity for the property) and the landscape contractor, many trees were procured in advance while the majority of the understory and meadow plants were contract-grown locally in Maryland. As the project was nearing completion, it became challenging to locate the size and species of trees required to maintain the design intent, which called for installation of higher-caliper trees. A more robust infrastructure of site-grown or contract-grown trees may have served to ameliorate some of these challenges.
- Despite a conscious material selection effort to reduce impermeable surfaces through the use of crushed gravel surfacing in the parking groves, Montgomery County code did not allow for gravel parking to be considered permeable. As a result, bioretention areas had to be created downslope of all three parking groves to capture “surface runoff” even though the crushed gravel is permeable, which represents an overengineered solution to satisfy code. There was a positive outcome that resulted: the required bioretention areas presented an opportunity to develop a diverse understory planting palette which has thrived beyond expectations.
- Over many years of implementation, the continued benefit of a long-term master plan was often noted. As the project(s) evolved and developed, having strong yet adaptable design strategies allowed additional parcels and programmatic elements to be integrated into the overall vision of Glenstone.
Catenary lighting in parking groves: Selux LED Pendant
Gallery bridge lights: BK Lighting
LED path lights: Hunza
Entry court walls, path stair treads, and parking grove wheelstops: Local Carderock stone from Tri-State Stone
Water Court pond coping, arrival hall paving, parking grove markers: Coldspring
Crushed stone: Vulcan Graham II Quarry and Luck Aggregates (both located in Virginia)
Trees: Halka Nurseries; Select Trees; Hammell Nurseries; White House Natives; and Ruppert Nurseries
Landscape Architect: PWP Landscape Architecture
Client: Glenstone Museum
Architect: Thomas Phifer and Partners (Phase 2 - Pavilions); Gwathmey Siegel & Associates Architects (Phase 1 - Gallery)
Agricultural and Soil Management Consultant: Matthew Rales
Arborist: Bartlett Tree Experts
Civil Engineer: VIKA
Environmental Engineer: BuroHappold Engineering
Fountain Designer: Dan Euser Water Architecture
Fountain Engineer: Biohabitats
General Contractor: HITT Contracting
Graphics, Signage, and Wayfinding Designer: 2 x 4
Horticulturist: Darrel Morrison
Irrigation Designer: Sweeney and Associates
Lighting Designer: ARUP
Master Stone Mason: Phillip Dolphin
Meadow Consultant: Larry Weaner Landscape Associates
Owner’s Representative: Mark G. Anderson Consultants
Soil Scientist: Pine & Swallow Environmental
Structural Engineer: Skidmore, Owings & Merrill
Role of the Landscape Architect
The landscape architect began working with Glenstone in 2003 when the firm was selected to develop a landscape on the 40-acre site surrounding the residence and the original museum building, The Gallery. This role evolved into developing an expanded plan for the original 150-acre estate (Phase 1). In 2011, Glenstone and the landscape architect worked together to develop a large-scale expansion plan to enlarge the site to over 300 acres (Phase 2). The landscape architect was closely involved with selecting the architect, siting the new building, and identifying desirable adjacent properties that could support an expanded site plan. The landscape architect continues to be involved with ongoing master planning and maintenance for the site.
Case Study Prepared By
Research Fellow: Emma Mendel, Lecturer, University of Virginia
Research Assistant: Chloe Nagraj, MLA Candidate, University of Virginia
Firm Liaison: Seth Rodewald-Bates, PWP Landscape Architecture
Mendel, Emma, and Chloe Nagraj. “Glenstone.” Landscape Performance Series. Landscape Architecture Foundation, 2019. https://doi.org/10.31353/cs1560