This page introduces sources for the selection of plants for stormwater BMPs, salt tolerance, and green roofs.
The following agencies provide up to date information on plant material selection for vegetated stormwater BMPs .
There are two specific situations in which these above sources should not be used: high salt concentrations (in spray and soil) and green roofs. Recommendations on salt tolerant and green roof plant material selection are given below.
Locations where salt tolerance is a concern include roadsides receiving frequent winter snowmelt spray, vegetated swales or basins where snowmelt runoff infiltrates the soil, and water bodies receiving relatively large volumes of snowmelt. This discussion is limited to selection of vegetation for constructed stormwater BMPs and vegetated areas receiving runoff from high use transportation routes and parking lots, wet and dry infiltration basins associated with regional ponding, county and state roadway swales and filter strips, and winter road snow dumping areas.
Salt tolerance is not a concern for stormwater BMPs such as rain gardens and infiltration swales in low to moderate use local streets and catchments with little or no salt-laden snowmelt runoff.
Salt tolerance is common to many plants of coastal marshy areas. These species are reliable on the east and west coast in their indigenous ranges. Some of these species are very widespread. The populations found in the Midwest are not necessarily salt tolerant. For inland areas the availability of naturally occurring populations of salt tolerant species is limited.
Salt tolerance has been shown in some of the dry grassland species of the west. The range of these species may include Minnesota. The local populations may exhibit salt tolerance and are recommended.
Salt tolerance has also been shown in some of the aggressive and invasive species found in the Midwest. These species, although amenable to the high salt areas are not recommended because of the stress that may be introduced to native plant communities. Depending on the species, their seeds may travel fairly far by wind or water and are not recommended for rural or urban areas, even if native plant communities are not adjacent.
Stormwater BMPs with high salt concentrations will be susceptible to invasion by exotic and invasive species due to multiple stressors from the salt, along with sedimentation and high phosphorus concentrations and petroleum products. Common buckthorn, one of the aggressive Midwest exotic species of saturated soils, has high salt tolerance. Box elder, a native of lowlands, but often a colonizer in disturbed sites also has high tolerance. Reed-canary grass has moderate tolerance, and purple loosestrife has high tolerance.
The table below lists species and plant seed mixes which should be reliable in soils with high salt concentrations. The tolerance to salt spray may vary, and is shown in parentheses if known. The plant materials listed do not include highly aggressive and invasive species.
Salt tolerance ratings can vary across the country and between investigators, depending on the ways the data are collected and the ratings categories selected. Rating systems are not standardized between various investigators for different plant types (trees, shrubs, herbs) and uses (agriculture, horticulture). The sources sited here were used to represent as best as possible recent research, regional evaluations, and results from specialized salinity testing laboratories.
Note that information on salt tolerance for Minnesota plants warrant some interpretation. Much of the salt tolerance information published nationally is oriented toward agriculture rather than stormwater BMPs. The first table below attempts to interpret data from the literature for applicability to Minnesota. The second table below provides sources for seed mixes.
Recommended salt tolerant mixes
Link to this table
|DESCRIPTION: Combination native and turf mix. Reaches a height of approximately 18 inches. For use inurban areas where conditions may be saline, droughty & generally poor soils. Oats to be substituted for Winter Wheat in spring plantings at a ratio of 1 to 1. RATE: 60 lbs/acre (67.2 kg/ha)|
|Common Name||Scientific Name||# Pounds||Percentage|
|Grama Sideoats||Bouteloua Curtipendula||4.80||8.00%|
|Grama Blue||Bouteloua Graciis||3.60||6.00%|
|Prairie Clover Purple||Dalea Purpureum||1.20||2.00%|
|Wildrye Canada||Elymus Canadensis||2.40||4.00%|
|Wheat Grass Slender||Elymus Trachycaulus||3.60||6.00%|
|Rye Grass Annual||Lolium Talicum||4.80||8.00%|
|Wheat Winter||Talicum Aestivum||15.60||26.00%|
|Bluegrass Canada||PCA Compressa||7.20||12.00|
|Grass Alkali||Puccinella Distans||9.60||16.00%|
|Bluestem Little||Schizachyrium Scoparium||6.00||10.00%|
|Dropseed Sand||Sporobolus Cryptandrus||1.20||2.00%X|
|Pounds of cover crop to be bagged seperately (Tech Memo 04-09-ENV-02||78.00|
|Mixture 10B (western Tall Grass Prairie): Grasses are PLS Forbs & introduced are bulk, yellow tag when available. DESCRIPTION: Native mix. Reaches a height of 36 to 48 inches. For use in western Minnesota. Oats to be substituted for Winter Wheat in spring plantings at a ratio of 1 to 1. RATE: 30 lbs/acre (33 kg/ha)|
|Common Name||Scientific Name||# Pounds||Percentage|
|Bluestem Big||Andropogon Gerardi||1.80||6.00%|
|Grama Sideoats||Bouteloua Curtipendula||2.40||8.00%|
|Wildrye Canada||Elymus Canadensis||1.80||6.00%|
|Wheat Grass Slender||Elymus Trachycaulus||1.20||4.00%|
|Wheat Grass Western||Elytrigia SmithA||0.60||2.00%|
|Rye Grass Annual||Lolium Talicum||3.00||10.00%|
|Wheat Winter||Talicum Aestivum||10.20||34.00%|
|Forbes F-1 or F-2||N/A||1.50||5.00%|
|Switchgrass Wild Type||Panicum Virgatum||0.30||1.00%|
|Bluestem Little||Schizachyrium Scoparium||3.00||10.00%|
|Indian Grass||Sorghastrum Nutans||3.00||10.00%|
|Needle Grass Green||Stipa Viridula||1.20||4.00%|
|Pounds of cover crop to be bagged seperately (Tech Memo 04-09-ENV-02||51.00|
Some common Midwest species are known to be intolerant of high salt soil concentrations. Avoid planting these species or seed mixes when salt is expected to be a stressor.
The green roof BMP has the most specialized circumstances for plant materials and thus requires a very different list of materials compared to on-the-ground BMPs. More than any other BMP, it is unwise to proceed on selecting green roof plant materials without full knowledge of the entire green roof structural design system. This has to do with the very constrained growing conditions for this highly engineered BMP. Note that the following discussion relates to plant selection for green roofs and is not a design sheet for green roof BMPs.
The first consideration on plant material selection is the basic green roof design type. Extensive green roofs (EGRs) have been commonly using xeriscape types of plantings in a shallow, draughty growing medium. These types of plantings are more appropriate for urban rooftops (See the table below for planting recommendations). Intensive green roofs (IGR) include earth-bermed structures and tend to be heavier and reliant on richer, deeper substrates and may also have shrubs and trees. As such, the plant materials for extensive and intensive green roof systems are not usually the same. For example, the selections for an earth-berm IGR planting may be quite different from an EGR system. It should be noted that plant species and diversity can affect ecological function
Non-native succulent species appropriate for extensive green roofs in Minnesota. Note: Many species of sedums grow well on green roofs in Minnesota. The list below shows some of the most common species. Many other Sedum species can also perform well.
Link to this table
|Scientific name||Common name||Plant height (inches)||Approximate bloom time||Flower color||Sun exposure||Winter interest|
|Allium schoenoprasum||Chives||10||Spring||White||Full sun to partial shade||Dormant|
|Sedum album||Stonecrop||6||Summer||White||Full sun||Red|
|Sedum hybridum 'Immergrünchen'||Stonecrop||6||Summer||Yellow||Full sun||Orange/bronze|
|Sedum kamtschaticum var. floriferum'Weihenstephaner Gold'||Russian Stonecrop||5||Summer||Yellow||Full sun||Red|
|Sedum kamtschaticum||Russian Stonecrop||6||Summer||Yellow||Full sun||Red|
|Sedum reflexum 'Blue Spruce'||Stonecrop||8||Summer||Yellow||Full sun||Blue-green|
|Sedum rupestre 'Angelina'||Golden Stonecrop||5||Summer||Yellow||Full sun||Coral/orange-red|
|Sedum sexangulare||Stonecrop||4||Summer||Yellow||Full sun to shade||Red|
|Sedum spurium 'Dragon's Blood'||Two Row Stonecrop||4||Summer||Red||Sun||Red|
Native species that have been grown successfully on extensive green roofs in Minnesota
Link to this table
|Scientific name||Common name||Plant height (feet)||Approximate bloom time||Flower color||Sun exposure||Found to require irrigation in some projects or studies||Found to survive with little or no irrigation in some studies or projects|
|Allium cernuum||Nodding Wild Onion||1 to 1.5||July-August||Pink||Full sun to part shade||X3,4|
|Allium stellatum||Prairie Wild Onion||1 to 2||July-August||Pink||Full sun to part shade|
|Andropogon gerardii||Big Bluestem||2 to 6||n/a||n/a||Full sun to part shade||X1,2,*|
|Anemone patens||Pasque flower||0.5||April-May||Purple||Full Sun to Part Shade|
|Antennaria neglecta||Field pussytoes||0.5||April-June||White||Full Sun to Part Shade|
|Antennaria plantaginafolia||Pussytoes||1||April-June||White||Full sun to part shade|
|Aquilegia canadensis||Columbine||2 to 3||May-July||Red/Yellow||Full sun to part shade|
|Asclepias verticillata||Milkweed||1 to 1.5||June-August||White||Full sun to part shade|
|Aster ericoides||Heath aster||1 to 3||July-October||White||Full sun to part shade|
|Aster laevis||Smooth aster||1 to 3||August-October||Blue-violet||Full sun to part shade||X4|
|Aster lateriflorus||Calico aster||2||August-October||White||Full sun to part shade|
|Aster macrophyllus||Large-Leaved aster||1 to 2||August-October||Lilac||Full sun to part shade|
|Aster novae-angliae||New England Aster||3 to 5||August-October||Red-violet||Full sun to part shade|
|Aster oolentangiensis||Shyblue aster||3||August-October||Blue||Full sun to part shade|
|Aster sericeus||Silky aster||1||September-October||Purple||Full sun to part shade|
|Bouteloua curtipendula||Side-Oats Grama||1 to 3||n/a||n/a||Full sun||X1,*|
|Bouteloua gracilis||Blue Grama Harebell||0.5 to 1||n/a||n/a||Full sun||X1,5,*|
|Campanula rotundifolia||Harebell||1 to 1.5||June-September||Blue||Full sun to part shade|
|Carex pensylvanica||Pennsylvania sedge||0.5||n/a||n/a||Full sun to full shade|
|Carex vulpinoidea||Brown Fox Sedge||1 to 3||n/a||n/a||Full sun to part shade|
|Chamaecrista fasciculata||Partridge Pea||2 to 3||July-September||Yellow||Full sun to part shade|
|Coreopsis palmata||Bird's Foot Coreopsis||2||June-August||Yellow||Full sun to part shade|
|Dalea purpurea||Purple Prairie Clover||1 to 2||June-July||Yellow||Full sun||X4||X1|
|Fragaria vesca||Wild strawberry||0.5||May-June||White||Full sun to part shade|
|Fragaria virginiana||Wild strawberry||0.5||White||Full sun to part shade||X4||X1,*|
|Geranium maculatum||Wild geranium||1||April-June||Pink||Full sun to full shade|
|Geum triflorum||Prairie smoke||0.5||April-June||Red||Full sun to part shade||X1,*|
|Heuchera richardsonii||Alumroot||1||May-June||Greenish white||Full sun to full shade|
|Koeleria pyramidata||June grass||2||n/a||n/a||Full sun to part shade||X4||X1,2,3|
|Liatris aspera||Rough Blazing Star||1.5 to 4||August-September||Rose, lavender||Full sun to part shade||X4|
|Liatris cylindracea||Cylindric Blazing Star||1||July-October||Purple||Full sun to part shade|
|Penstemon grandiflorus||Large-Flowered Beard Tongue||2||May-June||Purple||Full sun to part shade|
|Phlox divaricata||Woodland Phlox||0.5 to 1.5||April-June||Blue||Part shade to full shade|
|Polemonium reptans||jacob's Ladder||1||April-June||Blue||Full sun to full shade|
|Ruellia humilis||Wild Petunia||1||June-August||Purple||Full sun|
|Schizachyrium scoparium||Little Bluestem||3||n/a||n/a||Full sun to part shade||X4|
|Solidago nemoralis||Gray Goldenrod||0.5 to 2||August-October||Yellow||Full sun|
|Solidago ptarmicoides||Upland White Aster||1||July-August||White||Full sun|
|Sporobolus heterolepis||Prairie Dropseed||2 to 4||n/a||n/a||Full sun to part shade||X4||X1|
|Thalictrum dioicum||Early Meadow-Rue||1 to 2||May||Greenish yellow||Full sun to part shade|
|Tradescantia bracteata||Bracted Spiderwort||1||May-July||Purple||Full sun|
|Tradescantia occidentalis||Western Spiderwort||2||May-July||Blue||Full sun|
|Tradescantia ohiensis||Ohio Spiderwort||3||May-July||Blue||Full sun to part shade||X3,4|
|Viola pedatifida||Bearded Birdfoot Violet||0.5||April-June||Purple||Full sun to part shade|
1Based on trial green roofs at Chicago Botanical Garden, Richard Hawke, Personal Communication
2Based on Kevin Carroll, personal communication, 2013.
3Based on research at Michigan State University, Rowe in Sutton et al 2012b
4Based on research at Michigan State University, Monterusso et al 2005. In this study, plants were irrigated the first growing season, and irrigation was then abruptly stopped July 10 of the second growing season, during an unusually warm and dry summer; plants were not irrigated at all during the third growing season.
5Based on observations at Phillips Eco-Enterprise green roof, The Kestrel Design Group personal communication, 2013.
*Goes dormant or turns brown with little or no irrigation in drought but rebounds when water is available again.
Secondly, the plant material selection, through biological processes and nutrient cycling, may effect whether the BMP exacerbates or mitigates the function of nutrient storage. Research to date comparing EGRs and control (nongreen) roofs shows that green roofs are a poor BMP for nutrient storage and removal from precipitation. In evidence from both southern and northern climates, total phosphorus concentrations are higher in runoff leaving a green roof compared to control roofs, although the mass loading is the same as the control (Moran et al., 2004). Nitrogen losses from a green roof do not differ significantly from control roofs. So for nutrient loading and design of removal systems, other BMP tools should be located ‘further down the runoff path’ from the rooftop BMP to trap runoff from green roofs. It is unclear how the IGRs function for nutrient storage.
Extensive green roofs are definitely a reliable BMP for reducing peak runoff rates. This has been demonstrated in several controlled studies in both southern and northern climates. Intensive green roofs provide the same function. It is not clear if the plant material plays a significant role in this or whether it is related to the design of the planting medium and underlying roof runoff system. To date it has always been assumed that the overall design should support plant materials that are tolerant of drought conditions and not prolonged saturated soil.
There is plenty of opportunity for experimentation on green roof plant material. Most controlled experiments have been limited in the kinds of plant material tested. The Genus Sedum has been widely used in extensive green roof plantings. It is unknown whether plantings dominated by other and widely different plant groups will yield the same results. As such, the function of a green roof as a stormwater BMP may vary: nutrient storage may not be an issue with some plant materials. Until further case studies and experiments are conducted on the nutrient storage function of this BMP, it is wise to assume that all plant material selections will yield added nutrient runoff, particularly if the plants are fertilized. Thus, the green roof system should be designed in series with other BMPs which are expected to function in this respect.
The variety of choices of EGR plant material for warm and cold climates is generally limited in the following ways:
Plant selection is restricted to materials which will be successful in very shallow substrates, perhaps 6 inches, up to 12 inches deep. Long-lived, perennial drought tolerant species commonly display deep taproot growth or deep fibrous root systems. This is the main reason that the Genus Sedum is so commonly relied upon. In contrast, many of the prairie forbs and grasses valued for infiltration BMPs may not be appropriate for green roofs.
The plant material selection for any one specific green roof is also dependent on the substrate content and depth. Intensive and extensive systems were already defined, and will significantly effect the substrate choices. The plant material selections provided here have been limited to those for EGRs. Even within an extensive system, in which the substrate is in general droughty, the specific design of each system will significantly effect plant productivity. Experiments in which the same plant material was grown on several different substrates demonstrates the importance of this. As such, one of the main criteria for selecting EGR plants is the substrate design. And often, this is limited by the structural integrity of the building, particularly for retrofit designs.
For EGRs, irrespective of the specific design, one general consideration applies to establishing plant material. The material will usually be introduced as young plants, and to reduce transplant shock and provide an enriched environment for further growth, an organic substrate such as compost should be used as the immediate transplant medium.