Olympia (360) 943-0480Snohomish (360) 563-9648

Rain Gardens and Bio-swales

Rain Gardens and Bio-swales can be a large part of sustainable Low Impact Development. Incorporating these design elements into your landscapes will help to take up excess water and filter it before it enters groundwater systems.

These areas mimic wetland natural areas and sometimes natural forested areas, with the mix and placement of plants. The effect is quiet lovely. Rain gardens and bio-swales can include a variety of plants including trees, shrubs, grasses and herbaceous plants. See our list below for more details.

Rain Gardens

A rain garden is a shallow landscape depression with native soil or a soil mix and plants that can capture stormwater from small, adjacent contributing areas. They generally are areas with sloping sides so different plants can be employed at various levels, depending on how much moisture they can retain and use. Plants in rain gardens can withstand standing water and often have systems that work to absorb excess water, rather than allowing it to runoff and erode native soils.


Biorention swales are similar to rain gardens in that they are a depressed area of plants and soil, used to catch excess stormwater and runoff. Bio-swales are designed with even more drainage solutions in mind, as part of a system that can handle large quantities of runoff when other systems are flooded. Bio-swales are often built in low-lying areas where water tends to naturally collect. Plants can be used to take up some of the excess and to create a handsome and hospitable landscape environment. However, optional under-drains can be included to help direct excess water to proper storm drains. Additionally, gradient controls, such as check dams, gravel mulch and catch basins, are used to reduce flow and manage erosion and sediment buildup.

Where to Use Them

Rain gardens and bio-swales can be employed on a small or large scale. These can be used in both residential and commercial properties to prevent flooding, improve drainage and deal with excess water on a property. They do not need to take up much space. Rain gardens can be installed in parking lot and round-about islands. They work well in landscaped areas of apartment complexes and shopping centers. Bio-swales work well along road ways and ditches, where water naturally pools.

Order Now

Take a look at our list of perennials, grasses, shrubs and other plants that are compatible with Low Impact Development. You can order any of these plants today. Give us a call with your orders and questions at 1-866-816-5080

Zone 1 Trees

Species/Common Name Exposure Mature Size Bloom Time Comments
Alnus rubra

Red alder

Sun/part shade 30′-120′ high and 25′ wide Highly adaptable, drought tolerant, nitrogen fixer
Salix lucida

Pacific willow

Sun 40′-60′ high and 30′ wide Tolerates seasonal flooding, do not plant near pavement or underground structures
Fraxinus latifolia

Oregon ash

Sun/part shade 40′-80′ high and 30′ wide Flood tolerant, small green-white flowers
Malus fusca

Pacific crabapple

Sun/part shade To 40′ high and 35′ wide Spring Tolerant of soil saturation, produces fruit, not recommended to get in larger than #5 pot.

Zone 1 Shrubs

Species/Common Name Exposure Mature Size Bloom Time Comments
Lonicera involucrata

Black twinberry

Part shade/shade 2′-8′ high April-May Tolerant of shallow flooding, yellow tubular flowers attract hummingbirds
*Myrica californica

Pacific wax myrtle

Sun/part shade To 30′ high May-June Inconspicuous spring flowers, drought tolerant once established
Physocarpus capitatus

Pacific ninebark

Sun/part shade 6′-13′ high May-June Drought tolerant, white flowers, seeds persist into winter
Rosa pisocarpa

Clustered wild rose

Sun/part shade 6′-8′ high May-July Tolerates seasonal flooding but also tolerant of dry conditions, pink clustered flowers
Salix purpurea ‘Nana’

Dwarf arctic willow

Sun/part shade 3′-5′ high


Grows well in poor soils, moderately drought tolerant, small yellow flowers
Spiraea douglasii

Douglas spiraea

Sun/part shade 4′-7′ high Takes seasonal inundation, spikes of small pink flower clusters

Zone 1 Emergents

Species/Common Name Exposure Mature Size Bloom Time Comments
Carex obnupta

Slough sedge

Sun/part shade 1′-5′ high Takes seasonally saturated soils, shiny foliage, excellent soil binder and drought tolerant
Carex stipata

Sawbeak sedge

Part shade 10”-3′ high Takes wet soil, excellent soil binder
*Juncus effuses

Common rush

Sun/part shade 1′-2′ high Summer Hardy and adaptable, drought tolerant, small non showy flowers
Juncus ensifolius

Daggerleaf rush

Sun 12”-18” high Wet soils, shallow water, excellent soil binder
Juncus tenuis

Slender rush

Sun .5′-2.5′ high Moist soils, tufted perennial
Scirpus acutus

Hardstem bulrush

Sun 4′-8′ high Favors prolonged inundation, excellent soil binder
Scirpus microcarpus

Small-fruited bulrush

Sun/shade 2′-4′ high Tolerates prolonged inundation, good soil binder, drought tolerant

Zone 2 Trees

Species/Common Name Exposure Mature Size Bloom Time Comments
Acer truncatum

Pacific, sunset maple

Sun To 25′ high and 20′ wide   Drought tolerant, very cold hardy, moderate growth rate
Amelanchier alnifolia

Western serviceberry

Sun/part shade 10′-20′ high and 25′ wide April – May Drought tolerant, large white flowers, purple to black berries, rust can be a big problem
Corylus cornuta

Beaked hazelnut

Sun/part shade 20′-30′ high and 15′ wide April – May Edible nuts, intolerant of saturated soils, catkins hold through winter
Crataegus douglasii
Black hawthorn
Sun/part shade 20′-30′ high and 25′ wide Spring Gravelly soils, small white flowers, black berries, 1” spines forms thickets
Fraxinus oxycarpa

Raywood ash

Sun 25′-50′ high and 25′ wide Spring Drought tolerant, grows in variety of soil types, can take extreme temperatures will not tolerate constant wind or fog, resists pests and disease
Rhamnus purshiana


Sun/shade 20′-40′ high and 25′ wide   Small greenish-yellow flowers, sensitive to air pollution, yellow fall color
Salix scouleriana

Scouler willow

Sun/part shade 6′-40′ high and 25′ wide   Drought tolerant, do not plant near paved surfaces or underground structures
Salix sitchensis

Sitka willow

Sun/part shade 3′-26′ high and 25′ wide   Tolerates seasonal flooding, do not plant near paved surfaces or underground structures
*Thuja plicata

Western red cedar

Part shade/shade 200’+ and 60′ wide   Tolerates seasonal flooding and saturated soils, long lived and prefers shade when young

Zone 2 Shrubs

Species/Common Name Exposure Mature Size Bloom Time Comments
Acer circinatum

Vine maple

Filtered sun/shade To 25′ Spring Tolerant of shade and clay soils, excellent soil binder, beautiful fall color
Hamamellis intermedia

Diane witchhazel

Sun/part shade 10′-20′ high and 10′ wide January-March Showy fall color, yellow orange, long lasting, fragrant coppery-red flowers, not drought tolerant, requires watering
Oemleria cerasiformis

Indian plum/Osoberry

Sun/part shade 5′-16′ high February-March Prefers shade, tolerates fluctuating water table
Philadelphus x lemoinei ‘Belle Etoile’

Mock Orange

Sun/part shade 5′-6′ high May-June Soil and pH adaptable, easily transplanted and established, fragrant, large white flowers, tinged red at base.  Variety is hard to find but species is not
Ribes lacustre

Black swamp gooseberry

Part shade 1.5′-3′ high   Reddish flowers in drooping clusters, dark purple berries
Rosa nutkana

Nootka rose

Sun/part shade 6′-10′ high April-June Tolerates inundation and saturated soils, aggressive spreader, fruits persist, less thorny then R. rugosa
Rosa rugosa

Rugosa rose varieties

Sun To 8′ high   Drought resistant, hardy, vigorous and aggressive, highly prickly, fragrant white to purple flowers, fruits persist
Rubus parviflorus


Sun/part shade 4′-10′ high May-June White flowers, red berries, will make thickets and spreads easily
Rubus spectabilis


Part sun/shade 5′-10′ high February-April Good soil binder, magenta flowers, yellow/orange fruit, early nectar source for hummingbirds, makes thickets
Sambucus racemosa

Red elderberry

Part sun/part shade To 20′ high April-May Small white flowers, bright red berries, vase shaped, pithy stems lead to messy form, prune for tidiness
Symphoricarpos albus


Sun/part shade 2′-6′ high   Excellent soil binder, drought and urban air tolerant, provides good erosion control, spreads well in sun
Vaccinium parviolium

Red huckleberry

Part shade/shade 4′-10′ high   Prefers loamy, acid soils or rotting wood, tolerant of dry, shady areas, red fruit, trick to transplant, low availability

Zone 2 Herbaceous

Species/Common Name Exposure Mature Size Bloom Time Comments
Aquilegia formosa

Western columbine

Sun/part shade 1′-3′ high Spring Tolerant of seasonal flooding, red and yellow flowers attract hummingbirds and butterflies
Asarum caudatum

Wild ginger

Part shade/shade To 10” high Mid spring Heart shaped leaves, reddish brown flowers
Aster chilensis

Common California aster

Sun 1.5′-3′ high June-September Moist soils, white to purple flowers
Aster subspicatus

Douglas aster

Sun .5′-2.5′ high June-September Moist soils, blue to purple flowers
Camassia quamash

Common camas

Sun/part shade To 2.5′ high May-June Lots of watering needed to establish, loose clusters of deep blue flowers
Camassia leichtilnii

Giant camas

  2′-4′ high May-June Need lots of watering to establish, large clusters of white, blue or greenish-yellow flowers
Iris douglasiana

Pacific coast iris

Sun/part shade 1′-2′ high Spring Withstands summer drought and seasonal flooding, white, yellow, blue, reddish-purple flowers, fast growing
Iris foetidissima

Gladwin iris

Sun/part shade 1′-2′ high May Well drained soils, pale lilac flower, also called stinking iris
Juncus tenuis

Slender rush

Sun .5′-2.5′ high   Moist soils, yellow flowers
Iris siberica

Siberian Iris

Sun 1′-2.5′ high Late spring Moist soils, deep blue, purple to white flowers
Tellima grandiflora


Part sun/shade 1′-3′ high March-June Prefers moist soils, yellowish-green to pink flowers
Tiarella trifoliate


Part sun/shade To 1′ high Early-mid summer Moist soils, some drought tolerance after established, can form dense colonies
Tolmiea menziesii

Piggy-back plant

Part shade/shade 1′-2′ high April-August Brownish purple flowers, makes and effective ground cover
Viola species


Part shade/shade .5′-1′ high Late spring-early summer Moist soils, yellow to blue flowers


Zone 3 Trees

Species/Common Name Exposure Mature Size Bloom Time Comments
Cornus spp.


Sun/part shade 20′-30′ high and 30′ wide May Reliable flowering trees with attractive foliage and flowers, may need water in summer
Prunus emarginata

Bitter cherry

Sun/part shade 20′-50′ high and 20′ wide May-June Intolerant of full shade, purple to black cherries, roots spread extensively and tree’s have high mortality rate
Prunus virginana

Choke cherry

  3′-25′ high and 15′-20′ wide Late spring-early summer Dry or moist soils, deep rooting, attractive white fragrant flowers, good fall color, low availability
*Pseudotsuga menziesii

Douglas fir

Sun 100′-250’  high and 50′-60′ wide   Medium to fast rate of growth, provides a nice canopy but potential will restrict placement
Quercus garryana

Oregon white oak

Sun To 75′   Dry to moist, well drained soils, slow growing, has acorns

Zone 3 Evergreen Trees

Species/Common Name Exposure Mature Size Bloom Time Comments
*Arbutus unedo

Strawberry tree

Sun/part shade 8′-35′ high and 8′-20′ wide November-December Tolerant of extremes, tolerant of urban/industrial pollution, white or greenish white flowers
*Calocedrus decurrens

Incense cedar

Sun 75′-90′ high and 12′ wide   Tolerant of poor soils, drought tolerant after established, narrow growth habit, slow growing
*Chamaecyparis obtuse

Hinoki false cypress

Sun/part shade 40′-50′ high and 25′-30′ wide   Very slow growing, prefers sun but tolerates shade, does not transplant well or do well in alkaline soils
*Pinus mugo

Swiss mountain pine

Sun/part shade 15′-20′ high and 25′-30′ wide   Slow growing, broadly spreading, bushy tree, hardy evergreen
*Pinus thunbergiana

Japanese black pine

Sun To 100′ high and 40′ wide   Prefers dry to moist soils, hardy, fast growing, low availability

Zone 3 Shrubs

Species/Common Name Exposure Mature Size Bloom Time Comments
Holodiscus discolor


Sun/part shade To 15′ high June-July Dry to moist soils, drought-tolerant, white to cream flowers, good soil binder
Philadelphus lewisii


Sun/part shade 5′-10′ high June-July Adapts to a variety of soils, drought tolerant, fragrant flowers
*Pinus mugo pumilo

Mugho pine

Sun 3′-5′ high and 4′-6′ wide   Adapts to moist soils, slow growing and very hardy
Potentilla fruticosa

Shrubby cinquefoil

Sun To 4′ high May-September Moist to dry soils, several cultivars available with varying foliage and flower hues
Potentilla gracillis

Graceful cinquefoil

Sun 1′-2′ high July Moist to dry soils, yellow flowers
Ribes sanguineum

Red-flowering currant

Sun/part shade 8′-12′ high March-April Prefers dry soils, drought tolerant, white to deep-red flowers attract hummingbirds, thornless
Rosa gymnocarpa

Baldhip rose

Part shade To 6′ high May-July Dry or moist soils, drought tolerant, small pink to rose flowers

Zone 3 Evergreen Shrubs

Species/Common Name Exposure Mature Size Bloom Time Comments
*Abelia x grandiflora

Glossy abelia

Part sun/part shade To 8′ high and 5′ wide Summer Prefers moist, well drained soils but drought tolerant, white or faint pink flowers
*Arbutus unedo ‘Compacta’
Compact strawberry tree
Sun/part shade To 10′ high Fall Tolerant of poor soils, good in climate extremes, white to greenish white flowers, striking red/orange fruit
*Cistus purpureus

Orchid rockrose

Sun To 4′ high June-July Drought resistant, fast growing, reddish purple flowers
*Cistus salviifolius

White rockrose

Sun 2-3′ high and 6′ wide Late spring Tolerates poor soils, tolerant of windy conditions and drought, white flowers
*Escallonia x exoniensis


Pink Princess Escallonia

Sun/part sun 5′-6′ high Spring-fall Drought tolerant when established, pink to rose colored flowers, good hedge or border plant, attracts butterflies.
*Osmanthus delavayi

Delavay Osmanthus

Sun/part shade 4′-6′ high March-May Tolerant of a variety of soils, attractive foliage and clusters of white fragrant flowers, slow growing
*Osmanthus x burkwoodii

Burkwood osmanthus

Sun/part shade 4′-6′ high March-April Drought tolerant once established, masses of small, white fragrant flowers
*Rhododendron ‘PJM’

PJM Rhododendron

Sun/part shade To 4′ high Mid-late April Moist to fairly dry soils, well drained organic soil, lavender to pink flowers
*Stranvaesia davidiana

Chinese photinia

Sun 6′-20′ high June Moist soils, white flowers in clusters, showy red berries, low availability
*Stranvaesia davidiana undulata

Prostrate stranvaesia

Sun To 5′ high June Moist soils, lower growing irregularly shaped shrub, great screening plant. Has very low availability
*Vaccinium ovatum

Evergreen huckleberry

Sun/part shade 3′-15′ high March Moist to slightly dry soils, small pinkish white flowers, edible berries in August

Zone 3 Evergreen Groundcover

Species/Common Name Exposure Mature Size Bloom Time Comments
*Arctostaphylos uva-ursi


Sun/part shade   April-June Prefers sandy/rocky, well drained soils, flowers pinkish white, bright red berries, slow to establish, plant closely
*Gaultheria shallon


Part shade/shade 3′-7′ high March-June White or pinkish flowers, reddish-blue to dark-purple fruit
*Fragaria chiloensis

Wild strawberry

Sun/part shade 10” high Spring Sandy well drained soils, flowers white, aggressive spreader
*Helianthemum nummularium


Sun To 2′ high and wide May-July Will tolerate many soil types, woody perennial, many varieties are available with varying flower colors
*Lavandula angustifolia


Sun/part shade To 1.5′ high June-August Adaptable to variety of soils, blue, lavender, pink to white flowers, semi evergreen, aromatic. Does not like PNW wet winters
*Mahonia nervosa

Cascade Oregon Grape

Sun/part shade To 2′ high April-June Dry to moist soils, drought resistant, yellow flowers, blue berries
*Mahonia repens

Creeping mahonia

Sun/part shade 3′ high April-June Dry to moist soils, drought resistant, yellow flowers, blue berries
*Penstemon davidsonii

Davidson’s penstemon

Sun To 3” high June-August Low growing evergreen, prefers well drained soils, drought tolerant, blue to purple flowers.

Zone 3 Perennials & Ornamental Grasses

Species/Common Name Exposure Mature Size Bloom Time Comments
Achillea millefolium

Western yarrow

Sun 4”-2.5′ high June-September Dry to moist, well drained soils, white to pink/reddish flowers
Anaphalis margaritaceae

Pearly everlasting

Sun/part shade To 18” high   Drought tolerant perennial, spreads quickly, attracts butterflies
Bromus carinatus

California brome

Sun/part shade 3′-5′ high   Dry to moist soils, tolerates seasonal saturation, low availability
Carex buchanaii

Leather leaf sedge

Sun/part shade 1′-3′ high   Copper-colored foliage, perennial clumping grass, tolerant of many soils
Carex comans ‘Frosty Curls’

New Zealand hair sedge

Sun/part shade 1′-2′ high June-August Finely textured and light green, compact, clumping perennial grass, drought tolerant when established
Coreopsis spp.


Sun 1′-3′ high   Dry to moist soils, drought tolerant, seeds attract birds, annual and perennial varieties
Echinacea purpurea

Purple coneflower

Sun 4′-5′ high   Prefers well drained soils, hardy perennial, may need water in dry times
Elymus glaucus

Blue wildrye

Sun/part shade 1.5′-5′ high   Dry to moist soils, shade tolerant, rapid developing but short lived (1-3 years) do not use as lawn grass
Dicentra Formosa

Pacific bleeding heart

Sun/shade 6”-20” high Early spring-early summer Moist, rich soils, heart shaped flowers
Erigeron speciosus

Showy fleabane

Sun/part shade To 2′ high Summer Moist to dry soils, dark violet or lavender blooms, fibrous roots
Festuca ovina ‘Glauca’

Blue fescue

Sun/part shade To 10” high May-June Blue-green evergreen grass, drought tolerant, shearing will stimulate new growth
Festuca idahoensis

Idaho fexcue

Sun/part shade To 1′ high   Bluish-green bunching perennial grass, drought tolerant
*Fragaria vesca

Wood strawberry

Part shade To 10” high Late spring-early summer Dry to moist soils, white flowers
Gaultheria shallon


Sun/shade 3′-7′ high March-June Dry and moist soils, white or pinkish flowers, reddish-blue to dark-purple fruit
Gaura lindheimeri


Sun 2.5′-4′ high   Perennial, fairly drought tolerant and adaptable to varying soil types
Geum macrophyllum

Large-leaved avens

Sun/part shade To 3′ high Spring Bright yellow flowers, other cultivars available, some may require more water
Geranium maculatum

Spotted geranium

Sun/shade To 1.5′ high July Moist, well drained soils, low perennial, pale pink, blue to purple flowers, low availability
Geranium sanguineum


Sun/part shade To 1.5′ high May-August Moist soils, deep purple, almost crimson flowers
*Helichrysum italicum

Curry plant

Sun To 2′ high Summer Hardy evergreen perennial, good companion to lavender, bright yellow fragrant flowers, low availability
*Helictotrichon sempervirens

Blue oat grass

Sun/part shade 1′-1.5′ high June-August Clumping bright blue evergreen grass, bluish white flowers
Hemerocallis fulva

Day lilies

Sun/part shade 1′-4′ high Summer Easy to grow and tolerant of neglect, hardy perennial, entire plant is edible
Heuchera americana

Coral bells

Sun/part shade 1′-2′ high June-August Easily transplantable perennial, red, greenish-white flowers, may need supplemental watering in dry season
*Heuchera micrantha

‘Palace Purple’

Sun/part shade 1′-2′ high June-August Bronze to purple foliage in shade, small yellowish flowers, evergreen perennial


Sun 3′-5′ high March-September Various native varieties, blue to purple, violet to white flowers
Lupinus bicolor

Two color lupine

Sun 4”-1.5′ high Spring Dry gravelly soils, small flowered annual
Lupinus latifolius

Broadleaf lupine

Sun To 1′ high June-August Dry to moist soils, perennial, bushy herb, bluish flowers, low availability
Lupinus polyphyllus

Large-leafed lupine

Sun To 3′ high Spring-summer Dry to moist, sandy to gravelly soils, perennial
Mahonia aquifolium

Tall Oregon grape

Sun/part shade 6′-10′ high March-April Drought resistant evergreen, blue-black fruit, bright yellow flowers, great low screening barrier
Maianthemum dilatatum

False lily-of-the-valley

Part shade/shade 3”-12” high Spring Moist soils, small white flowers, light green to red berries
Pennisetum alopecuroides

Fountain Grass

Sun/part shade 1′-2′ high August-September Tolerant of many soil types, clump forming grasses
Pennisetum orientale

Oriental fountain grass

Sun/part shade 1′-3′ high June-October Somewhat drought tolerant, small clumping, blooming grass, showy pink flowers
*Penstemon fruticosus

Bush penstemon

Sun 8”-10” high May Prefers well drained soils, evergreen perennial, drought tolerant, violet blue flowers 1” long attract hummingbirds
*Polystichum munitum


Part shade/deep shade 2′-4′ high   Prefers moist, rich soil conditions but drought tolerant, large evergreen fern
Rudbeckia hirta

Black-eyed susan

Sun/part shade 3′-4′ high Summer Moist to dry soils, showy flowers, hardy and easy to grow
Smilacina racemosas

False solomons seal

Part sun/shade 1′-3′ high April-May Moist soils, creamy white flowers, red berries
Solidago Canadensis

Canadian goldenrod

Sun/part shade 1′-2′ high Late summer-early fall Dry to moist soils, yellow flowers