Rooftop and Rain Gardens Rooftop and Rain Gardens?

3/1/2020

• Low impact development • Stormwater management • Slow and filter • Reduces heat loads • Pollinator habitat!

Jennifer Bousselot, Ph.D. Assistant Professor, Colorado State University Department of Horticulture + Landscape Architecture

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Soil for Rain Gardens

• Soil evaluation • Soil analysis • Ribbon test • Percolation test • 12 inches of water • Amend with sand or compost

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Basic Rain Garden Designs Example Plants for Rain Gardens

• Tiers • Lowest tier (intermittent wet) • Middle tier (mesic – wet to dry) • Highest tier (driest)

• Plants • Shrubs • Herbaceous • Grasses

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Lowest Tier: Shrubs Lowest Tier: Herbaceous

• Rocky mountain maple (Acer glabrum) • Swamp milkweed (Asclepias incarnata) • Thinleaf alder (Alnus incana subsp. tenuifolia) • Showy milkweed (Asclepias speciosa) • Water birch (Betula occidentalis) • Marsh sunflower (Helianthus nutallii) • Red-osier dogwood (Cornus sericea) • Wild iris (Iris missouriensis) • Chokecherry (Prunus virginiana) • Boulder raspberry (Rubus deliciosus) • Blue elderberry (Sambucus caerulea) • Snowberry (Symphoricarpos occidentalis)

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Lowest Tier: Grasses Middle Tier: Shrubs

• Big bluestem (Andropogon gerardii) • Rocky mountain maple (Acer glabrum) • Prairie cordgrass (Spartina pectinata) • Leadplant (Amorpha fruticosa) • Alkali sacaton (Sporobolus airoides) • Red-osier dogwood (Cornus sericea) • Native Sedges (Carex sp.) • Creeping mahonia (Mahonia repens) • Chokecherry (Prunus virginiana) • Golden current (Ribes aureum) • Boulder raspberry (Rubus deliciosus) • Three-leaf sumac (Rhus trilobata) • Snowberry (Symphoricarpos occidentalis)

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Middle Tier: Herbaceous Middle Tier: Grasses

• Common yarrow (Achillea lanulosa) • Blue grama (Bouteloua gracilis) • Poppymallow (Callirhoe involucrata) • Side-oats grama (Bouteloua curtipendulina) • Blanket flower (Gaillardia aristata) • Indian ricegrass (Oryzopsis hymenoides) • Bee balm (Monarda fistulosa) • Little bluestem (Schizachyrium scoparium) • Black eyed Susan (Rudbeckia hirta)

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Highest Tier: Shrubs Highest Tier: Herbaceous

• Rocky mountain maple (Acer glabrum) • Almost any Colorado native prairie plant! • Leadplant (Amorpha fruticosa) • Most Penstemons • Mountain mahogany (Cercocarpus montanus) • Rocky mountain beeplant (Cleome serrulata) • Red-osier dogwood (Cornus sericea) • Purple prairie clover (Dalea purpurea) • Chokecherry (Prunus virginiana) • Little sunflower (Helianthus pumilus) • Golden current (Ribes aureum) • Wild blue flax (Linum lewisii) • Buffaloberry (Shepherdia argentea) • Prairie coneflower (Ratibida columnifera) • Snowberry (Symphoricarpos occidentalis)

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Highest Tier: Grasses Rain Garden References

• Blue grama (Bouteloua gracilis) • Rain Gardens By Nigel Dunnett & Andy Clayden • Buffalograss (Buchloe dactyloides) • Field Guide to Colorado’s Wetland Plants By Denise Culver and Joanna Lemly. • Indian ricegrass (Oryzopsis hymenoides) • Native Plant Revegetation Guide for Colorado By David • Little bluestem (Schizachyrium scoparium) Bucker et al, Colorado Department of Natural Resources • swbiodiversity.org SEINet

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Plants on Rooftops?

• Rooftops are overlooked as available space in our landscapes • Green roof systems have been researched over decades • Green roofs are viable in all climates, including Colorado • CO native plants are native to shallow, well drained conditions

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Green Roof Rational Types of Green Roofs

• As urbanization consumes more land, impervious surfaces Intensive or Rooftop Garden Extensive or Ecoroof also increase • Deep substrate (>6”) • Shallow (<6”) • Issues emerge which were insignificant • More like raised beds • Lightweight • The need to manage stormwater, • The urban heat island effect, and • Diverse • Retrofit • Loss of arable land • Mitigation? • Vegetation

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Green Roof Basics Plant Details • Growth habit • Groundcover Substrate Plants • Accent plant • Engineered • Succulent groundcovers • Plant Categories • Rarely any ‘real’ soil • Predominantly Sedum spp. • Annuals G. Whittenbaugh G. Whittenbaugh • Mostly expanded • Many experimental • Herbaceous perennials aggregate • Succulents • Grasses • Evergreen/winter interest • Shallow, fibrous rooted • Not tap rooted • Drought tolerant

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4 3/1/2020 Museum of Contemporary Art of ContemporaryMuseum How can Rooftops Help CO Flora?

• Ideal places for rare plants Lupinus crassus by Bernadette Kuhn • Designed for specific species • Invasive weed issues are rare • Little predation or foot traffic • Several models exist in Europe • Urban corridors for pollinators • Designed as habitats for fauna • Increase natives in landscapes

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Boulder Residence

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Nederland Residence Community College of Denver

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Denver Botanic Gardens Children's Garden Colorado State University

Green Roof References

• Green Roofs for Healthy Cities: greenroofs.org • greenroofs.com • The Green Roof Manual by Snodgrass & McIntyre • The Professional Design Guide to Green Roofs by Dakin, Benjamin, and Pantiel • Planting Green Roofs and Living Walls by Dunnett Questions? & Kingsbury [email protected] • Green Roof Plants by Snodgrass & Snodgrass

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