Rain Garden Plan

Goal: Create a demonstration rain garden for educational purposes, using native plants suitable for pollinators, that eliminates flooding on the eastern lawn of the Truly House located on the Cascadia College/University of Washington Bothell campus.

Location: East side of Truly House

·      At least 10' from building foundation

·      Rock-armored inflow carries stormwater to garden from gutter at the left side of porch

·      Garden drains stormwater from southeastern corner of roof having surface dimensions 5.8 m x 8 m, giving area of 46.4 m²

·      Garden will have circular shape with 3.5 meter diameter (area equal to 20% of roof area drained)

·      Ponding depth: 15 cm (depth necessary when using 20% garden-to-impervious-surface drainage ratio, assuming percolation rate of 1.27 cm/hour)

·      No existing shrubbery will be moved or shaded out

·      Adjacent to West Campus Lane for good exposure to campus foot traffic

·      Replaces some of the lawn

Excavation

·      Site excavated to 2' depth

·      Bottom graded, scarified to 2" depth, then raked smooth

·      Filled with bioretention soil mix: 70/30 sand and compost

·      Berm built up around garden border – 2' wide, made of compacted native soil covered with compost/sand mix

·      Native species planted

·      Mulch thickly laid between plants and on berm

·      Gently slopes into rain garden from berm to avoid trip hazard

Irrigation

·      Programmable timer

·      Drip irrigation system

·      Water sourced from Truly House hose bib

·      Needed in summer for first three years

Installation Schedule

·      April 1 – April 15: Acquire plants, soil mix, mulch, irrigation system

·      April 16 – May 17: Excavate site, plant, mulch, install irrigation system

·      May 28 – June 7: Create and install signage

Image Source: Google Earth

Species Planted

Red flowering currant (large shrub)        Ribes sanguineum                               FACU

Full/part sun, dry/moist soil, pollinators, hummingbirds, pest-eating insects, birds

Common snowberry (small shrub)          Symphoricarpos albus                         FACU

Full sun/full shade, dry/moist soil, pollinators, hummingbirds, pest-eating insects, birds

Pacific ninebark (large shrub)                  Physocarpus capitatus                        FACW

Full/part sun, moist/wet soil, pollinators, pest-eating insects, birds

Red-osier dogwood (large shrub)            Cornus stolonifera                               FACW

Full/part sun, moist/wet soil, hummingbirds, pest-eating insects, birds

Tall Oregon grape (large shrub)               Mahonia aquifolium                             FACU

Full/part sun, dry/moist soil, pollinators, hummingbirds, pest-eating insects, birds

Salal (small shrub)                                    Gaultheria shallon                                FACU

Full/part shade, dry/moist soil, pollinators, hummingbirds, pest-eating insects, birds

Gooseberry (small shrub)                         Ribes lobii                                            FAC

Full/part sun, dry/moist soil, pollinators, hummingbirds, pest-eating insects, birds

Native Lupine (herbaceous)                     Lupinus latifolius                                  FAC

Full/part sun, moist/wet soil, pollinators, hummingbirds, pest-eating insects, birds

Tufted hair grass (herbaceous)                Deschampsia cespitosa                      FACW

Full sun, moist/wet soil, birds

Douglas iris (herbaceous)                        Iris douglasiana                                   FACU

Full/part sun, dry/moist soil, hummingbirds, pest-eating insects, birds

Tiger lily (herbaceous)                              Lilium columbianum                            UPL

Full/part sun, dry/moist soil, hummingbirds, pest-eating insects, birds

Wood strawberry (herbaceous)               Fragaria vesca                                    FACU

Full/part sun, dry/moist soil, pest-eating insects, birds

Yarrow (herbaceous)                                Achillea millefolium                              FACU

Full sun, dry/moist soil, pollinators, pest-eating insects, birds

Great camas (herbaceous)                       Camassia leichtlinii                             FACW

Full/part sun, dry/wet soil, pollinators, hummingbirds, pest-eating insects

Hardhack (large shrub)                             Spiraea douglasii                                FACW

Full/part sun, moist/wet soil, pollinators, pest-eating insects, birds

Scarlet monkeyflower (herbaceous)       Erythranthe cardinalis                         FACW

Full/part sun, moist/wet soil, hummingbirds, pest-eating insects

Swamp rose (small shrub)                        Rosa pisocarpa                                   FAC

Full/part sun, moist/wet soil, pollinators, pest-eating insects, birds

Sword fern (herbaceous)                          Polystichum munitum                          FACU

Full/part shade, dry/moist soil, birds

Slough sedge (herbaceous)                     Carex obnupta                                     OBL

Shade, wet soil, saline soil, birds

Common rush (herbaceous)                    Juncus effusus                                     FACW

Full sun, moist/wet soil, birds

Primrose (herbaceous)                             Primula cusickiana                               FAC

Full/part sun, moist, pollinators

Douglas' aster (herbaceous)                    Symphyotrichum subspicatum             FACW

Full sun, moist soil, pollinators, hummingbirds, pest-eating insects, birds

Plant information: Native Plants for Willamette Valley Yards 

Rain garden used for inspiration: 

Image Source: https://www.bentonswcd.org/rain-garden-ii/

Final design:

Signage

·      16" x 28"

·      Facing West Campus Lane

·      Rice paper sealed in resin, mounted in carbon fiber frame on carbon fiber posts

·      "Welcome to our Rain Garden"

·      Promotes rain garden use to public

·      Explains benefits

·      Attractive graphics with QR code to this website

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