Adapting to Sea level Rise: Economic and Ecologic Roles for Seashore Mallow

Although seashore mallow has application in inland saline or non-saline situations these thoughts are particularly about problems driven by climate change and sea level rise and its impact on the coastal ecotone. As sea level rises, perhaps at a more rapid rate than earlier in our lives, low lying farm fields that are often very productive under dry land cultivation and their buffers will become salinized, as will rivers, and some aquifers. Non-salt-tolerant nutrient management buffers between housing and other development will be lost and perhaps replaced by invasive species. Recent storm tides provide such evidence in coastal farm fields where, unless a “nurse crop” is present to encourage the growth of desirable wetland plants, Phragmites often colonizes the vacated land and in woodland borders. These thoughts have led us to use the term, “self- subsidizing” and to look for multiple products and services that could be obtained from seashore mallow to subsidize the cost of making the biodiesel. In fact, these goods and services may exceed the EE value of the biofuel. The diagram below shows our latest array of products and services identified for seashore mallow. Some are well researched and some are not yet examined in depth.

ecological-role-seashore-mallowThe series of bullets below gives an idea of the depth of investigation of the products and ecosystem.

Mallow Products

  • Oil – work in collaboration with Bryan Moser at Bio-Oils Research Unit at the National Center for Agricultural Utilization Research (NCAUR), USDA in Peoria. Mallow seeds from Delaware were used as a feed stock for the production of biodiesel and blends with petrodiesel were tested. Results were published in Renewable Energy 2012. Bryan says oil extraction and conversion can be easily integrated into soy processing.
  • Cellulosic ethanol – Bruce Dien at NCAUR did this work and it is published in the same article as the biodiesel work. The outer part of thestem gave good yields, but the core yield was very low, hence he involved Stephen Vaughn in working on other uses of the stem.
  • Stem fractions – Steve chopped the stems into pieces and separated them into size fractions. The finer fraction of the core was very effective as an absorbant for organic liquids and for kitty litter. Steve said mallow was the most absorbant material he has evaluated for that purpose. A manuscript by Steve and our group is available about this work and that about the bedding litter and hydromulch. The bedding had a slow compressibility and an unusual rebound quality when applied weight was removed. The outer bark has been made into thread for cloth by a group we collaborate with in China where we introduced mallow as a crop for newly “reclaimed “coastal soils. Those results are In press in Biomass and Bioenergy.
  • Pyrolysis derived fuels- Rudy Behrens of the B.E.A.R. Group evaluated the straw of seashore mallow for this purpose.
  • Bio-based polymers – The oil has been suggested as a candidate for polymer production by chemical engineers.
  • Meal – Analysis of the meal by several groups indicates a good amino acid spread and possibility for use of mammals. It has been suggested that the use by cattle is limited to a fraction of the protein because of the residual oil left when it is crushed. However, a salmon aquaculturalist said the residual oil would not be a problem with his animals since their natural food is high in oil content.
  • Honey -Nectar production is high and many bees and other insects are involved with pollination, however insects are not necessary since self pollination occurs readily.
  • Spent flowers -Uses for the spent flowers are being explored.
  • Roots-These are being considered for carbon sequestration for atmospheric CO2 to compensate for gases released by fuel produced. Roots are being investigated as a source of gums and other products for extraction when the perennial has reached a point where replanting is being considered.

Mallow Ecosystem Services

  • Eco-eco-buffer – Used as a crop at the upper ecotonal edge seashore mallow absorbs nutrients moving either way across the boundary and harvesting seeds and stems cycles the nutrients away from the zone. Thus, they do not wash into the aquatic phase in flooding water or runoff either as particulate or dissolved components after decomposition.
  • Nurse Crop – Graduate student, Nicole Voutsina, did her three year thesis study on this ecosystem engineering role of mallow. A manuscript on the topic is under review in Coasts and Estuaries.


John L. Gallagher & Denise M. Seliskar – University of Delaware, Halophyte Biotechnology Center, 700 Pilottown Rd., Lewes, DE 19958 (;; 302-645-4264; 302-645-4366)

Should I Consider Planting a Test Plot of Seashore Mallow in One of My Fields?

Consider Seashore Mallow

1. Can you grow traditional crops successfully everywhere on your farm?

If the answer is yes, don’t consider Seashore Mallow at this stage of its development unless you are interested in broadening your diversity of crops and /or just trying something new. Only recently has the plant from the brackish marshes been studied as a crop and its agronomic qualities are not as “sophisticated” as those of mainline crops, such as soybeans, corn, wheat, etc. That is, yields of grain, knowledge of possible disease and insect pests, shattering issues, and weed control are not as thoroughly researched as with crops that have been in the domestication process for thousands of years. Lines with superior qualities for agricultural products and ecosystem services are just now being identified. Although Seashore Mallow is tolerant saline and wet conditions it doesn’t require then to grow, in fact, it grows well on highly productive soils.
2. If traditional crops cannot be grown because of periodic flooding and /or salinization of the soil due to tidal flooding, Seashore Mallow might be a crop for your future.

Why Mallow? Seashore Mallow is a perennial member of the cotton family that is native to brackish marshes. Its evolutionary adaptations for living in soggy and salty soils, along with those features associated with its ancestral base in Africa, have consolidated in this single species (Kosteletzkya pentacarpos) a number of useful crop plant features. These are combined with features that provide ecological services and resistance to stresses afflicting an increasing number of acres of once productive farmland. These features include: perennial growth habit with older crowns producing multiple stems (~ 10 or more), flood tolerance, drought resistance (deep roots), salt tolerance to half-strength sea water, sorghum sized seeds, seeds with high viability in cold storage (20+ years), high oil content seed (22%), high protein seed meal, long fibers in the outer covering of stems, short light-weight very absorbent fibers in the stem core, flowers that produce abundant nectar, and self-pollinating flowers if pollinators don’t arrive by mid-day. These and other features can be exploited to produce a number of products and ecological services from virtually all parts of the plant. Seashore Mallow is not a “one trick pony.”

3. What specialized equipment is needed to grow and harvest these plants?

Nothing exotic is required. Ordinary farm equipment has been used to grow a three-acre field near Lewes, Delaware. Planting can be done either on traditional-tilled or no-till land with a row planter usually used for soybeans and corn. Sorghum plates handle the seeds very well. Pre-emergent herbicides have been applied as needed with a variety of sprayers. Harvesting has been done either by direct combining or by cutting the crop while it is a little green using a sickle-bar cutter mower/ stem crusher combination with the rollers set apart. After a few days a combine with a pickup head separates the seeds and straw. The straw is then raked into windrows, baled, and hauled to storage. The innovations about how to grow and handle the crop have been made on a farm near Lewes Delaware (Seashore Mallow Harvest photos). Expanding the number of farmers and locations where the plant is growing including farms with storm flood -prone field settings is important to the innovation process as the crop progresses.

4. What are these products and services and who will buy them if I produce them?

There are a number of products and services the plants can provide and they are shown and briefly discussed in the attachment (Economic and Ecological Roles for Seashore Mallow). At the present time there are no commercial operations making these products from the plants although many of the major ones have been produced and evaluated in cooperation with personnel at the USDA, National Center for Agricultural Utilization Research in Peoria, Illinois. Other products are in various stages of development by others as noted in the attachment. Since Seashore Mallow is new to the possible methods of adapting coastal agriculture to sea-level rise, there hasn’t been a supply of the commodity for commercial product production, hence no market at this point. It is anticipated that as a supply of Seashore Mallow raw material expands manufactures will take advantage of the opportunity to produce mallow products. This choice would be made for some products because they have superior qualities to the present feed stocks for similar products. In other cases the “sustainable and green” aspects of Seashore Mallow production (a perennial using soil and irrigation water, neither of which will support traditional crops) enhance the value over those from non-eco-friendly feed-stocks. However, not much can be bought with “anticipated.” Hence, we are seeking funds to offset the expenses of those testing this plant in their fields for production, but none are available at this time.

One ecological service a planting of Seashore Mallow can provides is that of a buffer between field and estuary. It impedes particulate movement and absorbs nutrients thus preventing the lateral movement of nutrients through the soil to adjacent aquatic systems. Since the aboveground plant material is harvested and carried away from the buffer, the zone does not become saturated and “leak” into the adjacent aquatic system. A second service is the storage of carbon below ground in the plant’s large perennial root system. Consequently, the carbon dioxide released into the atmosphere when biodiesel made from the plant’s seeds is burned is recaptured. These services have value for society in general, as well as the farmer and the grower should be compensated for this service. It maybe that one might plant a buffer of Seashore Mallow as part of a Managed Buffer where ecological services were the primary focus and harvesting for products secondary.

5. Would It be better to build a dike around my land, install some drainage channels, and a pump to remove excess rainfall and salty water if the dike is topped or breached during a storm?

It is hard to determine where and how high to build defense structures since it isn’t certain how fast relative sea-level will rise or how severe and frequent storms will come. The type of dike needed will depend on the location and the seaward dike face may be subject to severe erosion during storms unless it is armored. The dike, ditch, and pump solution is expensive and difficult to work around, but dike systems can be made to succeed, as they have from The Netherlands to eastern China and nearby in salt hay fields in New Jersey and rice fields in Georgia.

In addition to achievability, both economic and ecological considerations determine the prudence of construction. It may not be economical in the long term to dike the land and install water management structures if the water level rise is relatively slow and changing to a mallow crop would extend the economic viability of the land use with the right crop for many decades. On the other hand, if the change is very fast, the scale of the diking and water management may need to be so great that is not an economical option. In that case growing mallow for a few decades before letting the land transform into a wetland and perform the ecological functions of a nursery ground for economically important estuarine organisms and other roles wetlands play may be far-sighted. Had the field been diked, seaward wetlands and the services they provide would likely been lost, since with rapid sea level rise the marsh would likely not build vertically fast enough to keep up with sea level rise. In such a case, allowing the eventual transgression of the marsh over the low elevation of the field is a service to society and the farmer should be compensated.

If there are the other questions or points your wish to raise or if you are interested in finding out more about Seashore Mallow as a crop or possibly testing it on you land please contact.

Jack Gallagher ( or Denise Seliskar ( at the Halophyte Solutions Laboratory, Smith Laboratory, School of Marine Science &Policy, College of Earth, Ocean, and Environment, University of Delaware, 700 Pilottown Road, Lewes, DE 19959-1298.

Provisional Seashore Mallow Planting, Growing, and Harvesting Protocol

1. Seed bed preparation.

Background – We’ve prepared the seed bed both by tilling and by no-till using
herbicides (glyphosate and gramoxone) to kill the weeds. Where we have nonsaline
soil, weeds are a problem since we do not have herbicide-ready seashore
mallow. Since mallow is a perennial, buildup of a seed-bank of weeds can be a
problem. Morning glory, marestail, poke weed, dandelion, Virginia creeper, and
some grasses (foxtail, fall panicum) are some of the offending plants. If the time
between spraying and seeding is short, glyphosate is not a good choice since the
seedlings are sensitive to that herbicide. If perennial weeds are part of the mix
then tilling is probably the best option because the gramoxone probably won’t be
effective on older perennial weeds.

Current needs – Five acres ready to plant seashore mallow. Given the time and
not knowing the field conditions tilling would seem to be the best option, but
local knowledge of the setting could alter the decision.



2. Planting.

Background – To date we have used a row planter with 19 inch rows with seeds ~3-5 inches apart and about 1 inch deep. Sorghum plates are the right size for the mallow seeds. We haven’t tried drilling the seeds, but that approach could be used. In small plots we have used 12 inch rows and that worked fine with the DE 22 line of mallow. We have planted in mid-May to Mid-June.
Current needs – Five acres planted soon. Method dependent on discussion.
Provisional Seashore Mallow protocol-23. Pre-emergent herbicides.

Background – In the initial planting year we have used pre-emergent herbicides. Dual Max 1 pt per acre plus 0.25% surfactant in 25 gals of water/ acre. In subsequent years, a quart of Atrazine and 0.5 oz of Sandea is added to the mixture. A quart of gyphosate per acre can be applied to kill winter and early spring perennial and annual weeds. The Atrizine use was determined safe in trials by Mark VanGessel and that for Sandea and glyphosate by Tony Freeman in field tests.

Current needs – At the time of planting apply the Dual herbicide. In the second
year before emergence spray with the Dual, Atrizine, and Sandea.
4. Fertilizer.

Background – Fertilizer application is generally made based on soil testing.
Response trials are underway in New Jersey at the USDA Cape May Plant
Materials Center. Provisional Seashore Mallow fertilizerAs a relative of cotton and okra we believe Seashore mallow
has a high feeding rate on potash and is sensitive to nitrogen. High nitrogen will
favor stem growth over fruit development. For the current project we are
especially interested in the very absorbent stem fibers for bedding for poultry,
consequently high nitrogen is desirable. Of the micronutrients boron is especially
important to prevent abortion of seed pods. The optimum pH is probably
between 6.2 and 6.5. At the Freeman farm this year we applied 85 N 34 P 104K
per acre.

Current needs – Depends on field conditions. We want to push vegetative growth
this first year because the goal is to maximize stem production for poultry

seashore-mallow-field-person5. Irrigation.

Background – Some years we have irrigated at the Freeman farm and some year’s we have not. Irrigation, when it was done, was once or twice during the season. Obviously, a newly planted crop is more vulnerable to drought than an established one and those in the second year and older are most resistant. Some of the physiological characteristics that confer salt tolerance to seashore mallow also enhance drought tolerance. In areas where soils or irrigation water are salty the ability of the plants to tolerate salt makes those soils and water resources, rather than liabilities.

Current needs – Depends on water availability and weather conditions. The potential for irrigation, if necessary, is very desirable, but we would like to minimize its use.

6. Insect Pests.

Provisional Seashore Mallow fieldBackground – Occasionally we have found in older stands a build-up of flea-beetles and scentless plant bugs. We have found some flea-beetle resistance in several accessions, but none for the plant bugs as yet. Once we had Corman spray the Freeman’s field from the air with Warrior and Lannate. We have sprayed from the ground several times in our plots in Lewes for insects.

Current needs – Depends on conditions.

7. Post emergent herbicides.

Background – Southern States came down from Milford with a large sprayer to apply Poast as a grass herbicide.

Current needs – Depends on needs. With a good elimination of current weeds and pre-emergent application, weeds shouldn’t be a problem at least this first year.

8. Cutting and combining.

Background – We have cut the plants with a Ford version of a Haybine in early September. The time is chosen to be when the oldest seed pods are just beginning to shatter and the youngest are still not mature. We try to time the harvest to give us the maximum yield of mature good seeds. After the plants dry they are combined with a machine with a pickup head. We have direct combined on occasion, but we feel that the rough handling of the stems by that method results in more seed loss. We have been looking for a swather to purchase to use in place of the cutter conditioner that would be available for any grower to use. We believe its use would reduce shattering loss even more.



Current needs – This first year with our focus on stems for poultry bedding we may want to pass on seed harvesting and let the seeds shatter. Many will germinate in the spring and thicken the stand in the summer of 2015. If we don’t harvest the seeds, the harvest of the stems can be delayed somewhat in the fall of 2014. We would want to harvest seeds from the 2015 crop.

9. Baling.

Background – After combining, the straw is then windrowed and baled.

Provisional Seashore Mallow bailing

Current needs – Cut, windrow, dry, and bale.

10. Winter cover crop.

Background – We have planted a winter cover crop many of the years to reduce
nutrient loss and give freeze protection to the crowns of seashore mallow. Wheat
or rye was better than barley, which proved hard to kill in the spring burn-down.

Current needs – Plant wheat or rye as a cover crop.
These are brief backgrounds on what has been done in the past and ideas of what
we need done this year. We will provide the seashore mallow seeds and provide
$1000.00 per acre for five acres to be planted, tended, and harvested. We will
get the baled straw to use in a comparison study of seashore mallow with
traditional pine chip bedding. The grower will provide the fertilizer and herbicide
chemicals. We do not expect to need to have the area sprayed for insects, if so
we can either pay the grower to do it or he can contract it to be done by air at our
expense. The second year of the crop will have somewhat different needs,
namely it won’t need to be planted, but the seed will need to be harvested.



John L. Gallagher & Denise M. Seliskar – University of Delaware, Halophyte Biotechnology Center, 700 Pilottown Rd., Lewes, DE 19958 (;; 302-645-4264; 302-645-4366)

Salt-tolerant crop shows promise as chicken bedding, helping farmers with flooded fields

volkJack Gallagher grew up on a farm, but he never cared much for the squawking chickens pecking around. The Pennsylvania farm boy gravitated toward the coastline, where he built a career studying salt marsh vegetation as a marine scientist in the University of Delaware’s College of Earth, Ocean, and Environment (CEOE).

Yet the professor emeritus of marine biosciences has returned to his agricultural roots, having found a potential new use for salt marsh plants: chicken bedding.

“I never thought I’d be involved with chickens,” Gallagher said. “That’s the exciting thing about research: You never know where it’s going to lead.”

With funding from Delaware Sea Grant and private supporters, Gallagher has long studied seashore mallow, a salt-tolerant, flowering plant found along the Atlantic and Gulf coasts. His research may end up helping not only chickens, but also farmers facing saltwater damage to their fields from worsening coastal flooding.

In a new partnership with UD Cooperative Extension, the Delaware Environmental Institute (DENIN), Delaware Wild Lands, CEOE, Delaware Sea Grant and others, Gallagher and his wife, retired CEOE research scientist Denise Seliskar, will help grow seashore mallow for testing as an alternative material for poultry house bedding.

The team will plant seashore mallow in areas where flooding has left soil salty and difficult to raise traditional crops like soybeans. According to recent estimates, sea level is rising rapidly in Delaware compared to the rest of the country, and up to 11 percent of the state’s total land area may be inundated by the end of the century. Farmers’ fields are already starting to flood more often, become inarable due to salinization and get taken over by invasive plants like Phragmites australis.

Gallagher initially began studying seashore mallow as a natural way to mitigate against such saltwater contamination. Seashore mallow can serve as a buffer plant against coastal flooding, with the plant fending off Phragmites and its deep root system fighting erosion. Seashore mallow is attractive for planting in new areas because it has large seeds that are easy to harvest and mechanically plant.

Gallagher and Seliskar planted two seashore mallow test plots about 10 years ago, one at UD’s Hugh R. Sharp Campus and the other at a nearby family farm in Lewes, the latter of which was the first effort to scale a planting to use commercial farm equipment. Since then, they have investigated a multitude of uses for seashore mallow.

The seeds contain a high percentage of oil, making them a potential source for biodiesel feedstock — and the remaining seed meal usable as feed for cattle and fish. Other harvestable materials from seashore mallow include nectar for honey, thread for cloth and animal bedding.

“We’ve gotten a lot of different products out of the plant,” Gallagher said.

The 2010 BP oil spill inspired a volunteer researcher in his lab to explore seashore mallow’s absorbency, finding it to be effective at soaking up oil. Next, they and a U.S. Department of Agriculture partner in Illinois considered the plant as a base material for biodegradable kitty litter and hydromulch.

That sparked an idea among colleagues at UD.

“We started to say, ‘Well, if it has potential as an animal bedding, could that animal be chickens?’” said Jennifer Volk, a CEOE graduate and extension specialist for environmental quality and management with Cooperative Extension, pointing out that the poultry industry is an important economic sector in the Delmarva Peninsula.

Volk, Gallagher, UD Cooperative Extension’s Bill Brown and others will conduct a trial this spring, comparing seashore mallow bedding to pine shavings, the traditional material that has become increasingly costly and harder to find. They will also compare to two other bedding alternatives, Miscanthus and switchgrass.

The seashore mallow is chopped into roughly 1-inch pieces, making fluffy flakes to spread on the floor of poultry houses. The researchers will monitor the materials’ absorbency and the health of the chickens over the course of the study.

At the request of Delaware Wild Lands, DENIN helped bring the various partners together for early meetings on the project. Two DENIN Environmental Scholars are helping with the project as interns: CEOE undergraduate Harry Colmorgen will map agricultural land vulnerable to Delaware Bay flooding, and Alfred Lerner College of Business and Economics student Andrew Flemming will work on land-use agreements with property owners in Kent County.

“This is a truly interdisciplinary kind of project,” said Jeanette Miller, DENIN’s associate director of interdisciplinary programs. “If farmers in Delaware are able to grow a native plant like seashore mallow as an alternative to crops that are no longer suited for salt-impacted agricultural land, that would be a huge boon.”

With support from Delaware Sea Grant, the College of Agriculture and Natural Resources and additional grants, the project aims to plant 10 acres of seashore mallow by the spring of 2015. The team is looking at planted on land owned by Delaware Wild Lands.

In the process of the cross-University effort, Gallagher said he is finding himself interested to learn about the finer points of raising chickens. Bedding needs to sop away uric acid so the birds’ feet do not get irritated, while also insulating them from the ground. The litter also can’t be too dry, which can cause dehydration and respiratory illnesses.

It took a few decades, but the feathered flocks have started to grow on him.

“I like them better now,” Gallagher said with a chuckle.

Property owners of salt-impacted land who are interested in participating in the project can contact Jennifer Volk at or 302-730-4000.

Article by Teresa Messmore

Article can also be found on UDaily.

Rain Gardens

Revision Date: 31 January 2009
Rebecca Pineo, Botanic Gardens Intern
Susan Barton, Extension Specialist University of Delaware
Bulletin #127 

What is a rain garden and how does it work?

Recently installed rain garden at the University of Delaware’s Louise and David Roselle Center for the Arts.

Rain gardens, sometimes called bio-retention areas, are shallow depressions in the landscape that capture stormwater and allow it to gradually percolate into the soil. Planted with moisture-loving plants that help filter out pollutants, rain gardens provide an attractive way to reduce the impact of stormwater on the environment.

What are the benefits of rain gardens?

  • Manages stormwater on site. Rainwater is captured by a rain garden instead of flowing off-site, where it picks up pollutants on paved surfaces before flowing into storm drains and then into natural water bodies. Rain gardens reduce flooding and erosion associated with large amounts of stormwater entering streams during heavy rainfalls.
  • Helps recharge the water table. By capturing water and allowing it to percolate into the soil, rain gardens help replenish local aquifers.
  • Filters out pollutants to reduce contamination of groundwater. Ongoing research suggests that rain gardens can be quite effective at filtering out some of the most common pollutants in stormwater, including chemicals, metals, fertilizers, and pesticides. Charged soil particles can attract and absorb metals and chemicals; microorganisms decompose pathogens and organic litter; and plants can filter out and utilize the nitrogen and phosphorous contained in fertilizer runoff.
  • Delights the senses. The diversity of plant textures, colors and fragrances possible in rain garden plantings can enhance the appearance of a home landscape. For more information about how people benefit from gardens, consult the fact sheet “Human Benefits of Green Spaces,” available at
  • Attracts wildlife. Plantings that provide food, nectar and shelter for wildlife can help preserve biodiversity. For more information about maximizing the wildlife value of the landscape, consult the fact sheet “Supporting Biodiversity in the Garden,” available at 

Installing a Rain Garden

This section describes basic guidelines for rain garden construction. For more in-depth instructions, consult “Rain Gardens: A How-To Manual for Homeowners” from the University of Wisconsin-Extension, available online at


The best place for your rain garden is on gently sloping ground where stormwater drains off impermeable surfaces or turf grass, such as the downhill side of a patio, driveway, or lawn. You can also site it in a location 10–30 feet away from your building where flexible piping can be used to direct the flow of your downspouts. Do not locate a rain garden in a low spot on the property that drains poorly. Poorly drained areas may not support sufficient plant growth to function as a rain garden.

A rain garden must have level sides to effectively capture water; a flatter slope requires less digging. Slopes of 1-10% are ideal. Orient your rain garden so the long side is perpendicular to the slope—this will maximize the amount of runoff captured.

Building code requires any water retention device, including rain gardens, to be located at least 10 feet from any building as a guard against flooding. Also avoid building your rain garden over a septic system, or where the seasonally high water table is less than 2 feet from the surface. Any time you dig in your yard, you also need to confirm the location of underground utilities; in Delaware you can call Miss Utility at 1-800-282-8555.

Finally, try to locate your rain garden in an area that receives full to partial sun, as most plants that do well in rain gardens are sun-lovers. There is, however, a limited selection of rain garden plants that can tolerate shade.


The surface area of your rain garden will depend on the rain garden’s depth, the size of the area from which you are capturing runoff, and your soil type. Typically, rain gardens are roughly 10-20% the size of the source area; several smaller gardens may be used in lieu of one big one. Even if you do not have enough space for rain gardens that treat all of your site’s run off, remember that every bit helps—a rain garden is 30% more effective at draining runoff than a turf area of the same size.

You can use the following equations to calculate the approximate surface area, where:

  • Runoff area = surface area of the area that the runoff will be draining from; for example, the size of your rooftop, driveway, patio, or sloping lawn.
  • Depth of runoff = average amount of rainfall in a storm. For most storm events in the Mid-Atlantic region, the rainfall is less than 2 inches.
  • Rain garden depth: Recommendations for rain garden depth ranges from 3 inches to 12 inches. The deeper the rain garden, the smaller the required surface area required. Note that a larger slope will require deeper digging for the rain garden to be level.

[Runoff area (ft2) x depth of run off (inches)] ÷ rain garden depth (inches) = rain garden area (ft2)

For example, if your 4-inch deep rain garden will treat up to 2 inches of rainfall that drains from the downspout of 10 x 25 ft. roof, your rain garden will need to be 125 ft2, or 10 x 12.5 ft:

[125 ft2 x 2 in] / 4 in = 125 ft2

Preparing the site  

Site preparation depends largely on the soil type of your site. In sandy or well-draining loamy soil, you simply need to dig a level-bottomed depression with gently sloping sides. Use the excavated soil to build a berm around the garden, leaving an opening on the uphill side where runoff will enter. Two stakes with a level string tied between them can serve as a guide for creating a level-bottomed depression on sloped ground. Consult the drawings on the next page for more information about digging a rain garden.

Clay soils or compacted, poorly draining soils often require more intensive excavation to be effective. Excavate or till to 3 or 4 feet, and fill partway with a layer of coarse gravel. Then, cover the gravel with a layer of permeable filter fabric, followed by sandy, free-draining soil and then a top layer of topsoil. Incorporating compost into the topsoil provides nutrients and added drainage capabilities.

As you would prepare any garden bed, perform a soil test and add nutrients as needed. Consult the Sustainable Landscapes: Soils page at for more information on sustainable soil practices.

Graphics courtesy of University of Wisconsin-Extension and the Wisconsin Department of Natural Resources, from “Rain Gardens: A How-to Manual for Home Owners,” available at


Rain garden plants must be able to tolerate not only moisture, but also drought, as the rain garden is designed to drain water quickly. For this reason, many plants typical to wetland environments are not appropriate for a rain garden. Hardy herbaceous perennials are most commonly used, through a variety of shrubs and trees also perform well in rain garden conditions. For specific plant recommendations, consult the list at the end of this fact sheet.


  • Mulching. After planting, apply mulch at a depth of at least 2 inches to preserve soil moisture, suppress weeds, and reduce erosion. Shredded hardwood mulch is an effective, attractive option; be sure to avoid mulches that float (for example, pine bark). As your rain garden matures, maintain the protective layer of mulch, adding more as the lower layers decompose. Research has shown that over time, decomposing mulch helps maintain the pollutant-absorbing properties of the soil. Eventually, the plants may grow together and mulch will no longer be needed.
  • Watering. Until the plants become established over the course of a few months, the garden will need to receive thorough watering at least twice a week by either rainfall or irrigation. More water may be needed in hot summer weather. With proper plant choice to fit your climate conditions, the garden will require no supplemental irrigation after the initial establishment period, except perhaps during extreme drought.
  • Weeding. Control for weeds until good plant cover is established.
  • Pruning and other maintenance. Prune shrubs to remove dead stems or rejuvenate plants such as red twig dogwood whose new growth is more desirable. Proper plant selection should limit the need for much pruning. In late winter/early spring (before new growth begins), perennial stems from the previous season can be cut within a few inches of the ground.
Plants for a Delaware Rain Garden 

Herbaceous Perennials:

Amsonia hubrechtii

Amsonia ciliata; downy blue star

Amsonia hubrechtii; Arkansas blue star

Amsonia tabernaemontana; blue star

Aquilegia canadense; columbine

Arisaema triphyllum; Jack-in-the-pulpit

Asclepias incarnata; swamp milkweed

Aster novae-angliae; New England aster

Aster novi-belgii; New York Aster

Athyrium filix-femina; lady fern

Baptisia australis; false indigo

Hibiscus moscheutos

Boltonia asteroides; boltonia

Caltha palustris; marsh marigold

Campanula divaricata; southern harebell

Carex stipata; tussock sedge

Chasmanthium latifolium; sea oats

Chelone glabra; white turtlehead

Chelone lyonii; pink turtlehead

Cimicifuga racemosa; black snakeroot

Convallaria majalis; lily-of-the-valley

Eupatorium maculatum; Joe-pye weed

Lobelia cardinalis

Gillenia trifoliate; Bowman’s root

Helianthus angulstifolius; swamp sunflower

Hibiscus moscheutos; marsh mallow

Iris cristata; dwarf crested iris

Kosteletskya virginica; seashore mallow

Lobelia cardinalis; cardinal flower

Lobelia siphilitica; blue lobelia

Meehania cordata; Meehan’s mint

Vernonia noveboracensis

Monarda didyma; Oswego tea, beebalm

Muhlenbergia capillaris;  muhly grass

Osmunda regalis;  royal fern

Osmunda cinnamomea;  cinnamon fern

Panicum virgatum;  switchgrass

Persicaria virginiana;  tovara

Phlox paniculata;  garden phlox

Physostegia virginiana;  obedient plant

Rudbeckia fulgida;  black-eyed Susan

Rudbeckia laciniata;  green-headed coneflower

Solidago rugosa;  goldenrod

Sorghastram nutans;  Indian grass

Spartina pectinata;  cord grass

Spiranthes cernua;  nodding lady’s tresses

Stylophorum diphyllum;  celandine poppy

Tradescantia x andersoniana;  Virginia spiderwort

Veratrum viride;  Indian poke

Vernonia noveboracensis;  Common ironweed

Veronicastrum virginicum;  Culver’s root


Magnolia virginiana

Amelanchier laevis; Shadbush

Asimina triloba; pawpaw

Betula nigra; river birch

Diospyros virginiana; persimmon

Liquidambar styraciflua; sweet gum

Magnolia virginiana; sweetbay magnolia


Itea virginica

Cephalanthus occidentalis;  buttonbush

Clethra alnifolia;  sweet pepperbush

Cornus amomum;  silky dogwood   

Cornus sanguinea;  bloodtwig dogwood   

Fothergilla gardenii;  dwarf fothergilla

Ilex glabra; inkberry holly

Ilex verticillata;  winterberry holly

Itea virginica;  Virginia sweetspire

Lindera benzoin; spicebush

Sambucus canadensis; American elderberry

Viburnum dentatum; arrowwood



Additional Resources

Designing Rain Gardens (Bio-Retention Areas)

Rain Gardens

Rain Gardens: A How-to Manual for Homeowners

Rainscapes: Harvesting the Heavens



Bannerman, R. and E. Considine. (2003). Rain Gardens: A How-to Manual for Homeowners. University of Wisconsin– Extension and Wisconsin Department of Natural Resources. Retrieved November 10, 2008 from

Hunt, William F. and Nancy White. (2001). Urban Waterways: Designing Rain Gardens (Bio-Retention Areas). North Carolina Cooperative Extension Service. Retrieved November 10, 2008 from

Miss Utility of Delmarva. (2008). Miss Utility of Delmarva. Retrieved November 10, 2008 from

Obropta, Christopher, William J. Sciarappa, and Vivian Quinn. (2006). Rain Gardens. Rutgers Cooperative Research & Extension. Retrieved November 10, 2008 from

Potomac Conservancy and Montgomery County Department of Environmental Protection. Rainscapes: Harvesting the Heavens. Retrieved November 10, 2008 from