At the edge of Denver's Civic Center in Colorado, the Populus Hotel reimagines a half-acre site as a vertically integrated urban landscape. Inspired by the interconnected root of Aspens - that grow in a group-like pattern with an extensive, ever-expanding network - the design integrated streetscape, rooftop, and interior environments into a single ecological system. As part of an interdisciplinary design team, the Denver-based landscape architecture firm Superbloom Landscape Architecture collaborated with Studio Gang Architects, Urban Villages, Kimley-Horn, Studio NYL Structural Engineers & Fa??ade Designers, Dr. Jen Bousselot, Aparium, Wildman Chalmers Design, The Beck Group, and Green Roofs of Colorado to create one of the first carbon-neutral hotels in the world. The Populus Hotel opened in late-2024 and is considered the first carbon-positive hotel in the United States.

The streetscape serves as a "forest floor" with engineered soil cells, native plantings, and salvaged Honey Locust benches complementing shade trees and pollinator habitat. Above, a green roof canopy of Aspens and prairie-adapted perennials delivers seasonal interest and ecological function. Reclaimed timber from the nearby 16th Street Mall roots the project in local material history. This compact site now hums with life - visitors gather, linger, and connect. The design shifts a once-hardened corner of downtown into a layered, verdant public realm. By threading ecological performance with everyday use, the site offers a replicable model for climate-adapted urban hospitality and streetscape design.

Ecological Networks
The green roof and streetscape establish a dynamic urban wildlife corridor, reconnecting fragmented ecological niches within Denver's dense urban fabric. Modeled after the mutualistic underground networks of Aspen groves, the rooftop showcases Columnar Swedish Aspen 'Erecta'(Populus tremula) as vertical habitat anchors, rising from a matrix of native grasses and wildflowers selected for high habitat value and extended seasonal bloom.

The planting design supports a range of Colorado-native solitary bee species, such as the Blue Orchard Bee (Osmia lignaria) and Agile Long-Horned Bee (Melissodes agilis), which forage on drought-tolerant composite flowers like Prairie Coneflower (Ratibida columnifera), Whorled Tickseed (Coreopsis verticillata) 'Moonbeam'), and Giant Goldenrod (Solidago gigantea).

On the streetscape, oversized planters and structural soil cells provide a stable growing environment for climate-resilient trees and low shrubs like Pawnee Buttes (Prunus besseyi) and Black Chokeberry (Aronia melanocarpa), creating layered habitat structure and essential forage during early and late bloom periods.

Design Process & Collaboration

 
From the beginning, the project was shaped by close collaboration between the Landscape Architect, developer, architect, and city agencies, all aligned around a shared vision of design excellence and urban resilience. The team worked closely with city staff to build on streetscape requirements, special district guidelines, and soil constraints, ensuring the selected planting palette could withstand urban stressors like de-icing salts, compacted soils, and high traffic while still supporting biodiversity.

The rooftop landscape - developed in concert with the architectural and structural teams - was designed to provide strong vertical structure and seasonal variation, with columnar Aspens and tall, flowering perennials chosen for their visual prominence from at and above street level. This layered approach supports pollinators, birds, and small urban wildlife, reinforcing the building's identity as a habitat-rich corridor within Downtown Denver.

Material Stories
Midway through design, the team was informed that mature Honey Locust (Gleditsia triacanthos) trees from Denver's nearby 16th Street Mall - one of the city's most iconic civic spaces - were slated for removal. Rather than allow these trees to be chipped and discarded, the design team initiated a collaborative effort with the city, the contractor, an arborist, the developer, and local fabricator - Where Wood Meets Steel - to salvage the most viable specimens. The trees were carefully tagged, felled, and transported to be milled and dried locally, ensuring the material remained rooted in its regional context.

Working with Where Wood Meets Steel, the design team sought to preserve the natural architecture of the Honey Locusts. Key branching forms were intentionally retained and repurposed as structural legs and cantilevered supports - balancing expressive form with engineered stability. The benches were carefully composed to showcase the trees' organic gestures while achieving comfort, durability, and visual lightness. Each bench is unique, shaped by the growth patterns of the original tree and fabricated entirely within a hyper-local supply chain.

By embracing circular design and localized fabrication, the project transforms urban tree removal into an opportunity for meaningful reintegration. These benches exemplify how landscape architecture can blur the line between ecology, craft, and cultural heritage.

Yellow Blooms, Color, and Landscape Identity
The planting palette is anchored by a deliberate chromatic strategy referencing the bright yellow of Aspen foliage in autumn. Species such as Black-Eyed Susan (Rudbeckia hirta), Little Lemon Goldenrod (Solidago 'Dansoliteen',) and select native grasses produce vibrant yellow blooms that provide essential nectar for pollinators and create seasonal highlights throughout the year. This color strategy strengthens the visual and symbolic ties to the building's Aspen-inspired identity, enriching the sensory experience while emphasizing the region's natural heritage.

Urban Regeneration
To mitigate urban heat island effects and address the water-scarce realities of Denver's semi-arid climate, the landscape employs a layered suite of green infrastructure strategies rooted in performance and resilience. Streetscape trees are supported by below-grade, suspended pavement systems with engineered structural soil cells, providing over 1,000 cubic feet of uncompacted soil per tree. This volume supports extensive root development while facilitating oxygen exchange, nutrient availability, and stormwater infiltration at the root zone. These systems not only enhance canopy longevity but also help reduce surface runoff and mitigate peak
storm events.

The planting design emphasizes drought-tolerant, low-input species that deliver both ecological and aesthetic function. Grasses such as Blue Grama (Bouteloua gracilis) and Little Bluestem (Schizachyrium Scoparium), along with native forbs and sedges, improve soil permeability, reduce erosion, and provide year-round habitat for pollinators and other beneficial fauna. These species are selected for their ability to withstand urban stressors, including reflected heat, de-icing salts, and compaction.

Above, the green roof integrates a water filtration system specified in coordination with structural engineer Studio NYL to meet rigorous load bearing, drainage, and wind-uplift requirements. The assembly balances lightweight, high-drainage media with sufficient soil depth to support deep-rooted prairie plants such as Maximillian Sunflower (Helianthus maximiliani), Mexican Hat (Ratibida columnifera), and Prairie Compass Plant (Silphium laciniatum). These species were chosen for their exceptional adaptability to roof conditions - including limited irrigation, extreme temperature swings, and high wind exposure - while also supporting key native pollinator species and increasing urban biodiversity.

Human Experience
In this active urban environment, the landscape fosters moments of pause, social connection, and sensory engagement. Micro-social spaces, including caf?(C) terraces and bench clusters, invite guests and pedestrians to linger amid textured grasses and pollinator activity. Salvaged wood benches provide comfortable, tactile places for rest and reflection, connecting visitors to the layered narratives embedded in the place. Elevated rooftop views offer sweeping vistas of downtown Denver and the Front Range, reinforcing a strong sense of place and well-being. This synthesis of ecological function and human experience creates a living room for the city.

Model & Prototype for Denver's Resilient Landscapes
This integrated green roof and streetscape serve as a replicable model for dense urban projects seeking to harmonize ecological integrity, social vitality, and climate adaptation. By weaving habitat corridors, engineered soils, and reclaimed materials into a seamless system, the project demonstrates how small urban parcels can deliver outsized environmental and experiential benefits. It advances the discourse on carbon-positive development, proving that ambitious sustainability goals can be met without sacrificing human-scale design or sensory richness. As a pioneering example in Denver and the Intermountain West, the Populus Hotel landscape provides a resilient blueprint for future urban ecological design.