All cities in the United States have undesigned areas that develop what is called “spontaneous urban vegetation”—plants that establish themselves without human intervention or planning. These areas can be large, such as abandoned or vacant building lots, former farms and ranches, and river corridors. They can also be small opportunities for plants and plant communities in sidewalk cracks, between paving and buildings, or anywhere enough soil has accumulated to allow the sprouting of seeds, as was the case on New York’s High Line elevated railroad before it was so famously developed into the urban amenity it is today.
In well-developed cities, 5-10% of the total vegetation or more can be spontaneous. In Detroit, the amount of area abandoned to this undesigned vegetation is about 40% as the city has depopulated and thousands of homes have been removed.
Spontaneous urban vegetation has been widely touted by scientists and landscape architects for its environmental benefits that include but are not limited to:
excess nutrient absorption in wetlands,
heat reduction in paved areas,
soil and air pollution tolerance and remediation, and
food and medicine for people.
However, there has been very little discussion, or appreciation, of the role that this vast amount of urban vegetation can have on native pollinators.
The report is the result of a survey of native plant material users from across the entire Eastern United States, with 760 respondents, and includes written comments. The respondents are drawn from NGOs, government, and commercial entities involved in ecological restoration projects and native plant production.
Amidst gradual reopening in parts on the world, the COVID-19 pandemic continues to affect nearly every aspect of life, from personal interactions to business to learning to recreation. The American Society of Landscape Architects (ASLA) is sharing insights, observations, and impressions from ASLA members based around the country here on The Field. In recent weeks, we’ve shared updates and resources curated by the Community Design, Historic Preservation, and Children’s Outdoor Environments Professional Practice Networks’ leadership teams. Today, we share dispatches from the Planting Design PPN team:
Mark Dennis, ASLA – Washington, D.C.
Anne Spafford, ASLA, MLA – Raleigh, North Carolina
David Hopman, ASLA, PLA – Arlington, Texas
Mark Dennis, ASLA
Senior Landscape Architect, Knot Design
Like all work-at-home, school-at-home, everything-at-home families these days, our own needs for outdoor connections are more persistent and unyielding than ever. We are here in Capitol Hill just a few doors down from Lincoln Park, a key element of the L’Enfant plan and among the oldest parks in Washington. The surging activity at Lincoln Park during the pandemic provides proof of just how crucial even the most fundamental aspects of amenity planning are in our society, while simultaneously highlighting the profound, persistent lack of funding for preservation and maintenance.
One of the best parts of my morning routine is to take a brisk-paced walk with my wife through our leafy suburban neighborhood in Arlington, Texas. It is a great chance to catch up on events, enjoy the changeable weather patterns in North Texas, greet and (occasionally) get caught up with our neighbors, enjoy the mature vegetation, and get the blood moving before a busy day. The neighborhood has very low non-arterial traffic flow that allows people and cars to comfortably coexist on the asphalt streets that are without sidewalks. However, at several points along our route, it invariably happens—the rise of the machines! Our morning reverie is interrupted with deafening sounds and billows of pollution and dust from gasoline-powered lawn and garden equipment (GPLGE).
These “machines in the garden” are ever with us, as was recently confirmed by a visit to Bloedel Reserve on Bainbridge Island near Seattle. Bloedel is one of my favorite places to return to and I always take the opportunity when I am in Seattle. Unfortunately, my aesthetic reverie at Bloedel was impacted by power equipment during my visit this summer and then became one of the incitements for this post.
As landscape architects, we are often responsible for designing the landscapes that are maintained by these environmentally and aesthetically abusive machines. Many people have written over the years about lower-maintenance alternatives to lawns and hedges, but adoption has been painfully slow. There is also surprisingly little emphasis on the effects of GPLGE on environmental quality by ASLA and by regulators. In Texas, the primary regulator for emissions is The Texas Commission on Environmental Quality (TCEQ). Their website has many suggestions for improving air and water quality. Drilling down to Voluntary Tips for Citizens and Businesses to improve air quality will eventually lead to a webpage devoted to lawn and garden care. On this page there are tips for harvesting and saving water, organic gardening, native plants, using trees to save energy, using less pesticides and herbicides, etc. GPLGE is very conspicuously absent.
On August 12, 2018, I attended a meeting of a new committee created by the Environmental Water Research Institute (EWRI) of the American Society of Civil Engineers (ASCE). The task force, comprised of approximately 40 stormwater professionals, is titled: ASLA/EWRI Committee on Plants and Soils Performance in Green Stormwater Infrastructure (GSI). The committee will produce recommendations over the next few years that will be distributed in a booklet and online. This work will be specifically focused on providing better research-based guidelines for soil performance and plant performance as an overlapping, interrelated system rather than as individualized elements. The committee’s goal is to provide guidance on short-term, medium-, and long-term practices to ensure that systems maximize performance.
Additionally, other sub areas such as biodiversity, maintenance, and soil microbial functions will be considered. The landscape architects on the taskforce will take the lead in addressing aesthetics and other social parameters that can support or impede acceptance of Green Infrastructure as an important component of place making.
The first phase of the task force’s efforts is to create an annotated bibliography as an indicator of where research is headed and to reveal significant gaps that should be addressed. The literature review phase is being organized by Harris Trobman, Project Specialist in Green Infrastructure at the Center for Sustainable Development and Resilience, The University of District of Columbia. The committee needs good research-based literature, especially as it relates to the performance of plants in green infrastructure. If you have a favorite book or article that you would like to share, please send it to me by December 1, 2018, and I will format it for inclusion in the bibliography. Currently, the bibliography is reflective of the vast preponderance of research that has traditionally come from engineers and scientists. Please free to contact me with questions and/or comments as well. If you would like to format the citation yourself, I can send an example.
Planting Design Professional Practice Network (PPN) Meeting
Saturday, October 22, 12:45-1:30 PM
Jackson Square Meeting Room, PPN Live on the EXPO floor
At the Planting Design PPN meeting Saturday afternoon during the ASLA Annual Meeting and EXPO, we will discuss our PPN’s goals for the upcoming year, meet the members who have been shaping blog posts for The Field and plans for Online Learning webinars, and have an opportunity to sign up and volunteer to join the Planting Design leadership team. The short 45-minute meeting will also give us some time for a discussion about designing for intermingled plant combinations led by David Hopman, landscape architect, associate professor, and chair of the PPN, and Nigel Dunnett, Professor of Planting Design, University of Sheffield, UK. This is intended as a participatory event so bring your toughest concerns and best ideas to share about this important and emerging trend in planting design.
In addition to the Planting Design PPN meeting, there will also be a planting design-focused EXPO tour on Saturday, and the EXPO Reception featuring the PPNs on Sunday, 4:30-6:00 PM.
Planting Design PPN EXPO Tour (1.0 PDH LA CES/non-HSW)
Saturday, October 22, 9:45-10:45 AM
Tours will start from PPN Live on the EXPO floor
This post is about the maintenance decisions that can have a profound effect on the range of plants useful for an aesthetically qualified urban polyculture. Some of the issues are addressed in the spreadsheet that was presented in part 8 of this series. For example, relative aggressiveness will help determine if plants play well together or if one plant is almost sure to dominate. However, the discussion that follows is on factors affecting plant palette decisions that go beyond the intrinsic characteristics of each plant that is considered.
Polycultures of herbaceous perennial plants and grasses are low maintenance but will frequently be more useful for aesthetically qualified native urban polycultures if they are pruned two or three times a year. Just because a plant is native does not mean that it must be allowed to express only its non-maintained form. This is especially true when soil amendments and irrigation are used. Water, fertilizer, and soils that are richer than what the plant would normally grow in without human intervention tend to make the plants taller, fuller, and more aggressive than otherwise, and may even cause them to flop over, particularly when they are blooming. Selective pruning may actually bring their appearance and stature back closer to a “natural” state.
Another big advantage to selective pruning is that it broadens the range of plants that can fit the aesthetic criteria of a particular polyculture. For example, one of the best native plants we have for shade conditions in North Texas is Inland Sea Oats (Chasmanthium latifolium). It is tolerant of both drought and seasonal inundation, stays attractive throughout the year, and establishes and spreads very easily. However, with irrigation it can easily get 3-4 feet tall, which may not be a desirable trait in an urban polyculture where other lower plants could have a seasonal focus. By cutting Sea Oats in half early in the season, it can easily be maintained at 18 inches tall. Some of the plants can also be left taller as “scatter plants,” which is how we are maintaining the UT-Arlington polyculture featured in part 7 of this series.
Part 8 of this series detailed the rationale and methodology for extracting qualified native plant species for use in creating polycultures. This month’s post features a discussion of how to successfully combine the species into a low maintenance native polyculture that can take the place of a monoculture groundcover.
The 109 species selected for use in part 8 were sorted to find groupings unified by height, texture, line, color, or form. Two categories of plants were created for each of the main polycultures. The first is very aggressive groupings of lower plants that serve as the primary intermingled groundcover. The second group of plants for each polyculture are accent plants that are unified with the lower grouping by texture, line, color, or form, but also have a strong contrasting element that will show them to best advantage. These are either more transparent scatter plants or more opaque shrubby plants used more like rocks or small hill shapes.
Case Study: Extracting native polycultures for bio-retention structures at The Botanical Research Institute of Texas
Reconceptualizing a Plant Palette Using Native Polycultures
Part 7 of this series focused on small steps that can be taken by any planting designer that will gradually move their designs in the direction of aesthetically qualified native urban polycultures. This post begins the discussion of a more complex and rigorous approach that I used in North Texas. The complexity of the Dallas/Fort Worth/Arlington area of North Texas is confounding when considering the use of extracted native polycultures as design components. It is a sprawling and rapidly growing metropolitan area of more than seven million people that is larger than the state of Massachusetts.
The problems and opportunities associated with reconceptualizing nature in this non-temperate area clarify an understanding of the issues in other areas where integrating nature may not be quite as complex and problematic. A detailed discussion is presented below that illustrates a research methodology used to develop 10 contrasting native polycultures for ecological retention structures on the campus of The Botanical Research Institute of Texas (BRIT) in Fort Worth, Texas.
Using Research to Define Aesthetically Qualified Native Urban Polycultures in North Texas
In North Texas, as in many other areas of the United States, the information needed to extract a wide range of native polycultures is simply not available. Academics and research institutes have a unique role to play in developing this information as the following description demonstrates. This research is directed at a palette of plants for ecological retention structures (large scale rain gardens), but can also serve as a model that can be adapted for the plant palettes required for many other types of planting design in metropolitan conditions in the Great Plains of the United States and other biomes throughout the world.
Developing a Plant Palette that Balances Aesthetic Control, Environment, and Ecology
Developing a plant palette for metropolitan areas that moves beyond the native and adapted plant palette is a very challenging and necessarily a very long term proposition. The vast corporate, design, regulatory, and research infrastructure that has evolved to the current state of the art will change very slowly, as it has in the past. As with any innovation, it will first be seen as radical and even eccentric and there will be many stakeholders that will push back hard against the tide of change. There are a number of possible scenarios for moving forward towards a more resilient and ecologically and environmentally supportive landscape palette.
One likely scenario for the transition to a more balanced palette is an incremental approach that gradually introduces native species, varieties, and selections into the infrastructure of the green industry. This would be an evolution of the ‘native and adapted’ palette that has been emerging since the 1980s, perhaps accelerated by climate change and the ‘new normal’ of warmer conditions with wide swings in rainfall patterns, coupled with increasing water needs from a rapidly growing population. This evolving palette will represent the same basic approach currently used by many designers for the selection of plants. Designers will search for aesthetically pleasing groupings, or drifts, of discrete monocultures that meet the practical, aesthetic, and financial criteria desired, albeit in a more environmentally and ecologically sustainable way.
Part 5 of this series introduced three relevant strategies at the new George W. Bush Presidential Center that were employed to select future viable species of plants. The first two, using local plant consultants and recreating a local prairie ecosystem, are addressed in part 5. This month’s post will focus on the third strategy, using an aesthetically qualified native polyculture for large areas of turf at the Bush Center.
The idea of using a palette of indigenous (actual native) plants is currently largely the purview of a small, relatively sophisticated cadre of native plant specialists and enthusiasts. Reconciling two points of view—the desire to restore complete ecological ecosystems with their environmental and ecological benefits, and using native and other adapted plants with a more traditional design approach, requires a reconceptualization of natural plant communities within a cultural context.
This difficult problem must first be addressed at the macro scale by finding the most appropriate native ecosystems, within the overall biomes, that are most practical and useful for the extraction of species for a new environment, the ‘new nature’ created by development conditions in metropolitan areas. It must then be addressed at the micro scale by constituting the details of this new synthetic environment, the particular plant palette, so that it meets biological, cultural, personal, and environmental goals and achieves a better balance of the three areas of aesthetics, environment, and ecology. The native turf polyculture used at the Bush Presidential Center is a good example of using both of these strategies.
Part 5: Lessons from the Bush Presidential Center: Local Consultants and Urban Prairies
The G. W. Bush Presidential Center landscape is a good point of departure for a discussion of a variety of strategies for future viable plant palettes, as there were three relevant strategies employed for selecting plant species:
Using local consultants to check species for regional appropriateness,
Recreating a local prairie ecosystem in an urban context using ecological restoration consultants, and
Using an aesthetically qualified native polyculture.
The Bush Center is a 23-acre campus near downtown Dallas that features four distinctly different plant palettes. Almost the entire campus, designed by Michael Van Valkenburgh Associates, Inc., was designed with sophisticated sustainable strategies. A small internal Rose garden, however, uses a more traditional green industry plant palette and demonstrates a good balance of a small area of resource-intensive exotic species within a large, biologically diverse, resource-efficient landscape—with many species of native plants.
Part 4: Contemporary Native and Adapted Plant Palette
The rise in research and the popularity of using native and adapted plant palettes can be traced to the work of the Colorado Water Board in the early 1980s. They coined and copyrighted the term ‘xeriscape™,’ a combination of the word “landscape” and the Greek word “xeros,” which means dry. [1-2] Other terms have been created for similar approaches in other areas. In North Texas the term used by the North Central Texas Council of Governments is ‘Texas SmartScape™.’ According to their website, the program is designed to “Conserve water and save $Money$ on your water bills; beautify your home and local environment; attract native butterflies, hummingbirds and other wildlife; and prevent / help reduce storm water pollution!” 
The native and adapted plant palette has made a large improvement to the environmental cost/benefits ratio of using plants for ornamental horticulture. The prime driver has been water savings, a subject that many people can relate to, including people who are not focused on other environmental issues or who may be primarily looking to save money and reduce maintenance. The gardening approach using this palette is flexible and can even approach fine gardening standards while using far less resources. The focus of designs using these plants is usually still discrete monocultures, or ‘drifts,’ of single species of plants using unity and contrast techniques derived from traditional principles. There has been a trend in recent years towards more naturalistic intermingled plant combinations using this palette as well. It has been very well promoted by government, industry, the design community, and academia, thereby hastening the adoption of this important innovation. Plants that were very hard to find and very expensive a few years ago can now be found at very low prices in many big box retailers.
The native and adapted plant palette is currently the state of the art when it comes to a proven and commercially-viable environmentally friendly strategy for selecting plants. It is the one that the most forward thinking landscape architects and garden designers use. Some of the tenets have even been written into landscape ordinances in drier parts of the United States. It is flexible, cost effective, and there is ample information easily available to train designers for success.
Part 3: The National Green Industry ‘Utility’ Plant Palette
The next step forward in moving towards a better balance of aesthetics, environment, and ecology has flourished since the latter part of the 20th century with the introduction of better adapted plants by the national horticulture industry. These are the ‘workhorses’ used by landscape architects to cover large areas of ground in landscape development and to provide the structure and spatial definition desired for landscape designs. They are hybridized species of turf, groundcovers, annuals, perennials, shrubs, and trees that are rarely indigenous to the areas where they are planted. The massive scale of the areas in the United States covered by these plants makes them the primary target for the aesthetically qualified native polycultures that are the subject of this series. Turfgrasses alone cover over 63,000 square miles—about the size of the State of Florida—and may be the largest irrigated crop in the United States. 
As in part 2 of this series on fine gardening, the priorities of the companies and the plant palettes they produce are revealed by examining the search functions on their websites. These websites show what the companies want their customers to look for and, significantly, what is missing from the thinking that is reflected in the plant palettes produced.
Part 1 of this series, published earlier this month, explained the goal of promoting a plant palette that balances aesthetics, environment, and ecology. This installment begins the discussion of a variety of plant palettes and planting design approaches with ‘Fine Gardening,’ a methodology that is very out of balance with the goal of aesthetic, environmental, and ecological balance. Fine gardening is an approach where the artistic intentionality of the designer and the direct sensuous experiences for the user are often the only priority. This approach is used in many high end residential projects, botanical gardens, and other landscapes where cost is not a determining factor. For example, at the Getty Center in Los Angeles, the gardeners take the heroic measure of hand-snipping twice a month every third leaf of each branch of the London Plane trees that line the path of the famous Robert Irwin garden, per Robert Irwin’s precise instructions. Fine gardening is promoted heavily in many newspapers and in magazines such as Southern Living, Fine Gardening, and many others.
Part 1: Aesthetics, Environment, and Ecology in the Creation of Plant Palettes
Essays about plants usually focus on specific plants, specific approaches to combinations of plants, practical uses for plants, plants for specific habitats, etc. These essays are indicative of the broad and continually evolving way that landscape architects approach planting design. This post takes a step back to address the issue of how landscape architects should use a clear set of principles to inform their palette of plants. By thinking first about the plant palette, new approaches to planting design will emerge that reflect the contemporary concerns of both the profession of landscape architecture and society at large.
Many design firms have design priorities that can be summed up in a few words. The ideas are sometimes illustrated with Venn diagrams and referred to as a triple (or quadruple) bottom line. The three criteria that are the focus of this series of posts are aesthetics, environment, and ecology. Other important elements, such as community and economics, can be addressed with a plant palette that balances these three important criteria. However, if art or economics, for example, are the driving generators of a plant palette, it may not be possible to bring the plants into balance with environmental and ecological concerns. Ecology is the most difficult and complex parameter to bring into balance and is currently the leading edge of future viable planting design innovation for landscape architects.
A variety of approaches to the selection of plants will be tested against the criteria of aesthetics, environment, and ecology in future posts. These posts will begin with a critique of palettes that are the most out of balance and proceed to others that gradually bring the three elements into equilibrium. The end of the series will propose a methodology for creating a palette of aesthetically qualified native polycultures suitable for the typical kinds of projects undertaken by landscape architects in metropolitan areas.