A PROGRAM OF NORTH CAROLINA COOPERATIVE EXTENSION

A PROGRAM

NORTH CAROLINA COOPERATIVE EXTENSION

Page 2

Table of Contents

& Common Rain Garden Questions Answered

& Quick Steps to Building a Rain Garden

& Further Information

ProgramTeam

Bill Hunt, N.C. Cooperative Extension Specialist for NCSU Biological and

Agricultural Engineering Dept.

Bill Lord, N.C. Cooperative Extension Area Agent, Franklin County Center

Mitch

Woodward, N.C. Cooperative Extension Area

Agent,

Wake

County

Center

Phyllis Baker Smith, Natural Resources Agent, N.C. Cooperative Extension,

Forsyth County Center

Like us on Facebook

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@NCSUStormwater

Manual by Wendi Hartup

NC State University and N.C. A&T State University are collectively committed to positive action to secure equal opportunity and prohibit

discrimination and harassment regardless of age, color, disability, family and marital status, gender identity, genetic information, national

origin, political beliefs, race, religion, sex (including pregnancy), sexual orientation and veteran status. NC State, N.C. A&T, U.S.

Department of Agriculture, and local governments cooperating.”

Page 3

What is a rain garden? A garden shaped into a

bowl-like depression in the ground to capture rainfall

runoff from your rooftop and driveway and allow

water to filter into the ground. The plants, mulch and

soil in a rain garden combine natural processes to

filter pollutants from runoff and break down in the

soil over time.

Why do we need rain gardens? Many of our

forests and other vegetated areas are developed into

impervious surfaces like parking lots, roads and

buildings. As plants are replaced with hard,

compacted surfaces, the rainwater is unable to

disperse energy and gradually soak into the ground.

Instead this stormwater races across pavement

picking up pollutants and sediment as it moves along

curbs and ditches to storm drains; which empty

directly into local waterbodies.

What are the benefits of rain gardens?

& Easy to design, install and maintain

& Come in all shapes and color schemes

& Provide aesthetic appeal while blending into

landscape

& Provide habitat for wildlife, butterflies and

beneficial insects

& Absorb nutrients and some heavy metals

& Enhance infiltration, stabilize soil and minimize

runoff to storm drains

What type of soil conditions are needed for a

rain garden? Rain gardens are essentially a water

infiltration device. Ideally the soil conditions for rain

gardens should have high percentages of sand with

some loam and/or clay content to support plant

growth and encourage infiltration (see red circle in

diagram below).

Rather than trying to change your soil conditions,

consider working with how your soil drains and

picking plants appropriate for that soil type.

Will this work without plants or just grass? Yes,

just aerating the soil reduces soil compaction but do

be sure to cover with some type of mulch. It will also

work with just grass but you will need to mow it at 4

inches or at the highest setting. Using plants helps the

rainwater to travel more efficiently through the soil

to recharge groundwater. Native perennial root

systems can extend 2 feet or more if the conditions

are right! Turf root systems usually only grow 4-6

inches deep.

Soil Texture Diagram

Page 4

What types of plants are suitable for a rain

garden?

& Tolerate periods of saturated soil, yet also

thrive under dry conditions

& Most natives

& Sustainable and low maintenance

What types of plants are NOT suitable for

a rain garden?

& Trees (growth changes sun conditions and

alters spacing available for other plants)

& Heavy feeders (ex. Crape Myrtle)

& Plants that do not like “wet feet” (ex. Asian

Azalea cultivars)

& Plants susceptible to root rot (ex. Flowering

Dogwood)

& Plants with aggressive root systems (ex.

Willows)

Does a rain garden form a pond? No. Rain

gardens are designed to allow a typical one-inch

rainfall to soak into the ground within three days

(Note: a wetland garden would allow water to

pool longer than 3 days).

Will there be standing water? Yes, after a rain

there will be water in your garden. It may even

look flooded. THIS IS OKAY! There may be 6”-9”

of standing water for up to three days. This

ponding will allow for the stormwater to slowly

infiltrate into the ground.

Are they a breeding ground for

mosquitoes? Not if they are draining properly.

Most mosquitoes need about a week to complete

their entire lifecycle. Mosquitoes are more likely

to lay eggs in bird baths, storm drains, corrugated

pipe attached to downspouts and lawns than in a

sunny rain garden. Also rain gardens attract

dragonflies, which eat mosquitoes!

Will I have to water the rain garden? After

planting, yes! First season, yes! In droughts, yes! In

rain, no!

Is a rain garden expensive? It doesn’t have to

be. The main cost will be purchasing the plants

(often these are already in the landscape or swap

plants with your neighbor) and mulch.

Apex, NC Town Hall Rain Garden

Sandy Ridge Community Center Rain Garden

Page 5

STEP 1: LOCATE THE RAIN GARDEN

Observe your yard during a rainfall event. Determine where

water begins flowing and where it is going. Rain gardens should ideally be

located between the source of runoff (roofs and driveways) and the runoff

destination (drains, streams, low spots, etc.). Be sure to consider the following:

& IMPORTANT: Do not place rain garden uphill of homes, septic systems or wellheads!

& Locate at least 10’ away and downslope of the house foundation, if crawlspace or basement (if

home is on a slab locate downslope of foundation).

& Locate 25’ away and downslope of a septic system drain field.

& Locate 10’ away and downslope of a well head.

& Avoid underground utility lines BEFORE you dig (Call 1-800-632-4949 or 811 in NC).

& The best location for the garden will be in partial to full sun (at least 4 hrs of sunlight).

STEP 2: DETERMINE DRAINAGE OF SOILS

Rain gardens work best when constructed in well-drained soils, but they can also be installed on sites

with less permeable soils with more clay content. Determining how the soil drains will help determine

the type of plants most likely to succeed in the rain garden.

Pick a few places and dig a one-ft-deep hole for the preliminary infiltration test; then fill with water a

few times. Time how long it takes for the test pit to drain. If satisfied with drainage time, dig 2-3 more

one-ft-deep holes in that area to get an average drain time. CAUTION: In floodplain areas or East of

I-95, dig two-ft-deep holes where high water tables are probable (highest in winter). The table below

summarizes what type of practice to use based on drain time.

Signs of an impermeable, compacted and/or wetland soil.

& The site ponds water or remains saturated for over four days after a storm event.

& Water poured in the dug hole is still there after four days, provided it hasn’t rained.

& The soil shows signs of being a wetland soil within a foot of the surface. A wetland soil is often

gray with ribbons or areas of brown color. It can also smell like rotten eggs.

Conduct drainage test at least twice at each hole! Also a good time to collect soil for

testing to determine proper lime application.

Drain Time Appropriate Rain Garden Type

< 12 hours Quick Draining Rain Garden

12 - 72 hours Standard Rain Garden

> 3 days Wetland Garden

Page 6

STEP 3: SIZE THE RAIN GARDEN

Determine which impermeable surfaces (roof top and driveway) will be treated with the rain garden.

Measure the length and width of these surfaces and multiply together to get the surface area in square

feet. This will be your watershed size.

The size of the rain garden should be at least 10% of the impervious surface draining to the rain garden.

Rain gardens should be designed to pond 10 inches of rainwater on top of the mulch. Rain gardens that

are 10% of the watershed and have a 10” ponding depth should capture the majority of one-inch storms.

(Length of surface x Width of surface) x .10 = total rain garden area sq. ft.

EXAMPLE: A portion of a 60’ by 60’ house (4 downspouts total) and 500 sq

ft of driveway runs off to the rain garden location. The rain garden will

capture 1 inch of rainfall, what size should the rain garden be?

Roof area plus driveway: 900 + 500 = 1400 sq ft

Divide square footage by 10: 1400/10 = 140 sq ft

A 11’X12’ or 14’X10’ garden design would be sufficient.

The size of your rain garden can also depend on the space available and your budget. If you don’t have

enough space, you can build multiple rain gardens or build a smaller one and plan for it to overflow more

often.

STEP 4: CONSTRUCT THE RAIN GARDEN

Consider how rainwater gets to your rain garden. Will the water sheet flow across the landscape from

the downspout? Will the water be piped underground to daylight into the rain garden?

Lay out the boundary of the garden to keep a shape. You can use a rope, spray paint or even flags to

outline your shape. Keep in mind how you determined the infiltration time period in Step 2.

NOTE: Always determine where utility lines are located BEFORE you start to dig. CALL 811!

ft900

60x60

areaRoof 

Helpful Tools

& Auger

& Tape Measure

& Shovels and/or Backhoe

& Rakes

& Pitchforks

& Trowels

& Tamper

& Wheelbarrow

& Line Level and/or Ruler

& Stakes and String

& Tarp

& Extra Labor

Page 7

& If present, remove and save sod for berm and weir

& Remove any topsoil and set aside.

& Dig to account for 10” ponding depth.

& Dig to account for 3” of mulch.

& Rough up 4”-6” of the bottom so it is not compacted

and mix in topsoil you removed earlier. This will not

only improve drainage but help plants survive. This is a

good time to apply lime if you took a soil test.

NOTE: Contact your County’s Cooperative Extension office for soil sampling boxes or

visit http://www.ncagr.gov/agronomi/sthome.htm/

Forming the Berm and Overflow Weir

Your rain garden is designed to capture the first inch of rainfall. Rainfalls larger than 1” will cause the

rain garden to overflow. Rain gardens should have distinct entrances and exits to prevent erosion.

Rain Garden Entrance

Establish a 1’-2’ grass strip, rock border or combination along the upper edge of the rain garden to

slow down the runoff water as it enters the rain garden. If piping downspouts to rain garden, make

sure the pipe opens up into the rain garden and is not buried.

Mulch

Organic Layer

(sod, mulch, etc.)

Topsoil Layer

(nutrient-rich)

Sub-Soil Layer

(often void of

nutrients)

Page 8

Rain Garden Exit

You will have lots of soil available from digging. Place extra soil on the downhill side of the rain garden

to create a berm, an earthen dam or barrier that holds water inside. Most rain gardens have berms

about 3” - 6” tall. Compact the soil slightly with your feet or shovel as you build the berm. Cover

with turf grass sod, mulch, plants, or rocks.

You will need to design a weir or nature will do that for you. A weir is an area of the berm that

allows water to gently pass over it. Typically weirs are a one-foot wide section of the berm and

several inches lower than the rest of the berm. To properly size the weir, use the amount of

impervious surface area (see table below). Weirs can be covered with turf grass sod or rocks;

additionally they can be made of wood. Make sure the weir is level and lower than the rest of the

berm.

www.bluegrassraingardenalliance.com

Impervious

Surface

Area

(ft

)

Overflow

Weir

Length

(ft)

2000 or less 1.0

3000 1.5

4000 2.0

5000 2.5

Weir Sizing Table

Guilford Cooperative Extension Rain Garden

Dixie Classic Fairgrounds Rain Garden

Page 9

Adding Plants

Pick your plants based on how your soil drains so you are working with nature instead of against it.

Below are example rain garden plans.

Drains in <12 hrs

Drains in 12 hrs - 3 days

Drains in >3 days

& Add 3” double or triple shredded hardwood mulch.

& Direct the downspout to the rain garden.

Muhly

grass

Daylily

Monarda

Switch Grass

Liatris

Sedum

Switch Grass

Sweetflag

Monarda

Sweetflag

Muhly

grass

Sweetflag

Juncus

Daylily

Sedum

Inkberry

Goldenrod

Cardinal

flower

Joe Pye Weed

Coreopsis

rosea

TurtleheadBeautyberry

e P

e W

Black-

eyed

Susan

Baptisia

Goldenrod

Deep Pool

1” - 6” Deep

1”-3” Deep

Bulltongue

Arrowhead

Water lily

Spatterdock

Pickerelweed

Broadleaf

Arrowhead

Sedge

Juncus

Pickerelweed

Lizard’s

Tail

Woolgrass

Softstem

Bulrush

Woolgrass

JuncusJuncus

Sedge

Page 10

STEP 5:WATER AND WEED THE RAIN GARDEN

Make sure to water every 7-10 days without adequate rainfall (1” per week) until plants become

established; usually takes the first year. Once established, plants should be watered in long periods of

drought.

Fertilizers are typically not necessary.

Refresh mulch annually. Loosen existing mulch and add only if needed up to 3 inches of mulch. Best

times to mulch are after 1st frost in fall or after last frost in spring, otherwise the plants could be

insulated too soon. Un-mulched surfaces may develop into a hardpan, a condition in which the soil

surface becomes cemented together, forming a hard, impervious layer. Make sure mulch is only 3-4

inches; too much mulch will reduce ponding and function of rain garden.

Weed regularly during plant establishment, as newly planted species may have a tough time competing

with weeds. Once plants become established, less weeding will be required.

Pruning may be needed to let some of the other plants grow. In the winter, leave dormant plants

standing and deadheads for bird food. Cut back in the spring.

Keep your garden healthy and clean. Rain gardens should be periodically cleared of dead vegetation

and any debris that may collect. Replanting may be necessary over time. If a plant is not doing so well

in one location of the garden, it may have to be moved to a wetter or dryer area.

Your garden may need a bit more maintenance than a lawn in the beginning, but in the long run it will

be easier to care for and provide many added benefits!

TASK SCHEDULE

Prevent Soil Erosion Keep watch on out parcels and parking lot use

Trash removal Weekly

Pruning Annual

Mulch renewal After 1st frost in fall or last frost in spring

Mulch removal Every 3 years

Weeding and Plant

replacement

As needed

Remove sediment As needed or during mulch renewal

Perimeter Mowing As needed, keep clippings out of rain garden

Rain Garden Maintenance Tasks and Schedule

Page 11

RESOURCES

Documents and websites consulted in the development of this document include:

Hunt, Bill. “How to Build Your Own Backyard Rain Garden.” N.C. Cooperative Extension.

http://www.bae.ncsu.edu/topic/raingarden/Entire_handout.doc

NC State

& http://www.bae.ncsu.edu/topic/raingarden/

& http://www.bae.ncsu.edu/stormwater

& http://plants.ces.ncsu.edu/

National Wetland Plant List. US Army Corps of Engineers.

http://rsgisias.crrel.usace.army.mil/NWPL/

The Oregon Rain Garden Guide: A Step by Step Guide to Landscaping for Clean Water and Healthy

Streams. Oregon State University.

http://seagrant.oregonstate.edu/sgpubs/onlinepubs/h10001.pdf

Rain Gardens: A How-to Manual for Homeowners. University of Wisconsin-Extension.

http://clean-water.uwex.edu/pubs/pdf/home.rgmanual.pdf

Rain Gardens: A Rain Garden Manual for South Carolina. Clemson University.

http://www.clemson.edu/public/carolinaclear/cc_toolbox/index.html

Ruth, Cliff. Plants for Constructed Wetlands and Rain Gardens.

http://www.ces.ncsu.edu/copubs/env/water/018/RaingardenPlantsBrochure.pdf

NATIVE PLANT SUPPLIERS

Many seed companies available online.

North Carolina Native Plant Society, http://www.ncwildflower.org/natives/sources.htm

FOR FURTHER ASSISTANCE, CONTACT YOUR LOCAL COOPERATIVE EXTENSION OFFICE

North Carolina, http://www.ces.ncsu.edu/

Nationally, http://www.csrees.usda.gov/Extension/index.html

Links to other internet locations may or may not have been provided in this article because they contain related

information that may be of interest to the reader. The North Carolina Cooperative Extension does not necessarily

endorse the views expressed or the facts presented on those sites. Further, N.C. Cooperative Extension does not endorse

any commercial products that may be advertised or available on those sites.

Revised April 2018

Forsyth County Cooperative Extension

145Fairchild Rd

Winston Salem, NC 27105

336-703-2850

http://www.forsyth.cc/CES

http://forsyth.ces.ncsu.edu

NC State University and N.C. A&T State University are collectively committed to positive action to secure equal opportunity and

prohibit discrimination and harassment regardless of age, color, disability, family and marital status, gender identity, genetic

information, national origin, political beliefs, race, religion, sex (including pregnancy), sexual orientation and veteran status. NC State,

N.C. A&T, U.S. Department of Agriculture, and local governments cooperating.”

NCDEQ Stormwater Design Manual

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C-2. Bioretention Cell 8 Revised: 11-23-2020

Table 1: Planting Plan Recommendations

Planting Plan Topic

Recommendation

Plant community

Should be diverse plant to avoid susceptibility to insects,

drought, and/or disease.

Sod media for sod

Sod must not be installed that has been grown in soil that has an

impermeable layer, such as clay.

Standards for plant materials

Plant material should conform to the current edition of American

Standards for Nursery Stock.

Upon delivery of plants, check:

Normal, well-developed branches and vigorous root systems,

and be free from physical defects, plant diseases, and insect

pests, tagged for identification, not root-bound.

Container size

In most cases, herbaceous plants installed in bioretention cells

are grown in containers holding 3.6 to 6.8 cubic inches of media

(for example, and not limited to, 72, 50 and IP 110). Other

container sizes or bare root stock may be appropriate for some

species and conditions. No container size is specified for trees

and shrubs.

Optimal planting time

Fall and winter planting are best (will vary for western Piedmont

and mountains). Spring is acceptable but will require more

summer watering than fall planting. Summer planting drastically

increases plant mortality and requires regular watering

immediately following installation.

How the plants should be planted

For best survival, trees should be planted with the top of the root

ball partially out of the media. For trees and shrubs, the top of

the root ball should be 1-3” above the media. If large trees are to

be planted in deep fill media, care should be taken to ensure that

they would be stable and not fall over.

Local jurisdiction codes

Local jurisdictions often have specific guidelines for the types

and location of trees and other landscape plants planted along

public streets or rights-of-way. Additionally, local landscape

ordinances must be followed. Contact local authorities when

making plant selections for your project.

Plants used in low impact development SCMs should be suitable for their purpose: Select non-

aggressive plants adapted to the region. Native species (USDA NRCS PLANTS Database

) are

preferred. However, well-known non-aggressive, non-seeding introduced species and/or

horticultural selections of native species may be appropriate for high visibility bioretention cells

to enhance public appeal. Do not use invasive species (

Southeast Exotic Plant Pest

Council), noxious weeds (NCDA&CS Noxious Weed List) or plants known to be weeds (Global

Compendium of Weeds).

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C-2. Bioretention Cell 9 Revised: 11-23-2020

Plants suitable for North Carolina bioretention cells are listed in Tables 2 through 4. Additional

plant species that are not shown in the table may also be suitable.

Table 2: Trees for Bioretention Cells

Latin Name

Common Name

Comments

Aesculus pavia

Aesculus sylvatica

Red buckeye

Painted buckeye

Amelanchier arborea

Amelanchier canadensis

Serviceberry

Height: 25-50 ft

Asimina triloba

Pawpaw

Betula nigra

River birch

Entire state (ht: 50-75ft)

Carpinus caroliniana

Ironwood

Cercis canadensis

Eastern redbud

Chionanthus virginicus

Fringe tree

Ilex opaca American holly

Liriodendron tulipifera

Tulip poplar

Nyssa sylvatica

Nyssa biflora

Blackgum

Swamp tupelo

Oxydendrum arboreum

Sourwood

Platanus occidentalis

American sycamore

Quercus bicolor

Quercus laurifolia

Quercus lyrata

Quercus michauxii

Quercus nigra

Quercus phellos

Quercus shumardii

Swamp white oak

Laurel oak

Overcup oak

Swamp chestnut oak

Water oak

Willow oak

Shumard oak

Taxodium distichum

Bald cypress

Piedmont to Coast; low drought resistance; not

salt tolerant. Height: 25-50 ft

Magnolia virginiana

Sweet bay magnolia

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C-2. Bioretention Cell 10 Revised: 11-23-2020

Table 3: Shrubs for Bioretention Cells

Latin Name

Common Name

Comments

Alnus serrulata

Tag alder

Aronia arbutifolia

Aronia melanocarpa,

Red chokeberry

Black chokeberry

Callicarpa americana

American beautyberry

Ceanothus americanus

New Jersey tea

Cephalanthus occidentalis

Button bush

Clethra alnifolia

Summersweet Clethra

Piedmont-Coastal Plain; flood and salt tolerance

Cornus amomum

Silky dogwood

Cyrilla racemiflora

Swamp Cyrilla (ti-ti)

Entire state; medium drought tolerance, some

salt tolerance

Diospyros virginiana

Persimmon

Eubotrys racemosus

Coastal fetterbush

Halesia carolina

Carolina silverbell

Hamamelis virginiana

Witchhazel

Hydrangea quercifolia

Oakleaf hydrangea

Hypericum densiflorum

Dense Hypericum

Entire state; flood & salt tolerant

Hypericum prolificum

Shrubby St. Johnswort

Entire state; flood & salt tolerant

Ilex decidua

Possum haw

Ilex glabra

Inkberry

Ilex verticillata

Winterberry

Ilex vomitoria

Yaupon Holly

High drought tolerance

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C-2. Bioretention Cell 11 Revised: 11-23-2020

Itea virginica

Virginia Sweetspire

Lindera benzoin

Northern Spicebush

Leucothoe fontanesiana

Leucothoe axillaris

Highland doghobble

Coastal doghobble

Lyonia lucida

Fetterbush

Rhododendron viscosum

Rhododendron atlanticum

Swamp Azalea

Dwarf Azalea

Entire state; medium drought tolerance

Physocarpus opulifolius

Ninebark

Rosa palustris

Swamp rose

Salix caroliniana

Salix sericea

Carolina willow

Silky willow

Sambucus canadensis

American black elderberry

Spiraea tomentosa

Steeplebush

Entire state; drought tolerant; pink flowers

Styrax americanus

American snowbell

Symphoricarpos

orbiculatus

Coralberry

Vaccinium arboreum

Vaccinium corymbosum

Vaccinium fuscatum

Farkleberry

Highbush blueberry

Black highbush blueberry

Viburnum dentatum

Viburnum prunifolium

Viburnum nudum

Arrowwood Viburnum

Blackhaw Viburnum

Possumhaw Viburnum

Entire state; flood tolerant & drought tolerant; salt

resistant

Xanthorhiza simplicissima

Yellowroot

Table 4: Herbaceous Plants for Bioretention Cells

Latin Name

Common Name

Comments

Acorus americanus

Sweet flag

Amsonia tabernaemontana

Eastern blue Star

Entire state; drought resistant; pale blue flowers

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C-2. Bioretention Cell 12 Revised: 11-23-2020

Andropogon glomeratus

Bushy bluestem

Asclepias incarnata

Swamp milkweed

Baptisia alba

Baptisia australis

White wild indigo

Blue indigo

Coast. White flowers.

Canna flaccida

Yellow canna

Carex amphibola

Carex cherokeensis

Carex comosa

Carex crinita

Carex grayi

Carex lupulina

Carex lurida

Carex muskingumensis

Carex radiata

Carex rosea

Carex squarrosa

Carex stricta

Carex vulpinoidea

Carex glaucescens

Carex intumescens

Creek Sedge

Cherokee Sedge

Longhair Sedge

Fringed Sedge

Gray's Sedge

Hop Sedge

Lurid Sedge

Palm Sedge

Eastern Star sedge

Rosy Sedge

Narrow-Leaved Cattail Sedge

Tussock Sedge

Fox Sedge

Waxy sedge

Bladder sedge

Chasmanthium latifolium

Chasmanthium laxum

River Oats

Slender Woodoats

Entire state; medium drought tolerance

Chelone glabra

White turtlehead

Cladium jamaicense

Saw grass

Coreopsis lanceolata

Coreopsis tinctoria

Tickseed

Dulichium arundinaceum

Three-way sedge

Echinacea purpurea

Purple coneflower

Eleocharis quadrangulata

Square-stem spikerush

Elymus canadensis

Elymus hystrix

Elymus virginicus

Wildrye

Eupatorium perfoliatum

Boneset

Entire state

Eutrochium dubium

(syn. Eupatorium dubium)

Eutrochium fistulosum

(syn Eupatorium

fistulosum)

Coastal Joe Pye Weed

Joe Pye Weed

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C-2. Bioretention Cell 13 Revised: 11-23-2020

Gaillardia pulchella

Blanket Flower

Helenium autumnale

Sneezeweed

Helianthus angustifolius

Swamp sunflower

Heliopsis helianthoides

False sunflower

Heuchera americana

Coral bells

Entire state; many different cultivars

Hibiscus coccineus

Hibiscus moscheutos

Scarlet rose mallow

Rose mallow

Not found in the mountains.

Iris virginica

Southern blue flag

Juncus coriaceus

Juncus effusus

Juncus tenuis

Leathery rush

Soft rush

Path rush

Entire state; medium drought

Kosteletskya pentacaropos

(syn. Kosteletskya

virginica)

Marsh mallow

Liatris spicata

Blazing star

Lobelia cardinalis

Lobelia elongata

Cardinal flower

Blue lobelia

Monarda fistulosa

Monarda didyma

Bee Balm

Panicum virgatum and

cultivars

Switchgrass

Entire state, few mtns; drought resistant

Pycnanthemum muticum

Pycnanthemum

virginianum

Mountain mint

Entire state

Ratibida pinnata

Gray-headed coneflower

Rudbeckia fulgida

Rudbeckia hirta

Blackeyed susan

Saururus cernuus

Lizard’s tail

Scirpus cyperinus

Wool Grass

Solidago canadensis

Solidago rugosa

Goldenrod

Entire state

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C-2. Bioretention Cell 14 Revised: 11-23-2020

Solidago sempervirens

Sorghastrum nutans

Indiangrass

Entire state; drought tolerant

Silphium perfoliatum

Cup plant

Symphyotrichum

lateriflorum

Symphyotrichum laeve

Symphyotrichum novae-

angliae

Symphyotrichum

oblongifolium

Calico aster

Smooth aster

New England aster

Aromatic aster

Verbena hastata

Blue vervain

Vernonia noveboracensis

Ironweed

Table 5: Turfgrass Specification for Bioretention Cells

In grassed bioretention cells, use perennial grasses such as hybrid Bermuda or centipede in

the CP and Piedmont, use cool season turf grass such as fescue or bluegrass in the

Mountains. Grass should never be seeded, use sod instead. When using sod, avoid sod that

is grown in soil that has an impermeable layer (such as clay).

NOTE: There are native turf trials going on at NCSU and additional species may be

recommended in the future.

BIORETENTION MDC 11: MU LCH

BIORETENTION MDC 11: MULCH.

For bioretention cells with vegetation other than sod, triple shredded hardwood mulch shall

be used for the portion of the cell that will be inundated. Mulch shall be uniformly placed two

to four inches deep.

Triple-shredded hardwood mulch has been found less likely to wash away than other forms of

mulch (such as pine). The mulch layer functions to reduce weeds; regulate soil temperatures

and moisture; reduce soil compaction and prevent erosion; and prevent soil and fungi from

splashing on the foliage. Mulch serves as a pretreatment layer by trapping the finer sediments

that remain suspended after the primary pretreatment.

Applying more than four inches of mulch can cause plants to grow in the mulch and not the soil,

which weakens them, particularly during drought. Mulch should be free of weed seeds, soil,

roots, and other material that is not bole or branch wood or bark.

Mulch needs to be periodically renewed to maintain a two to four-inch depth. The ideal time to

reapply mulch is in the late spring after the soil has warmed. Every few years, mulch should be

removed and replaced.