Rain Garden Plants

The Plants

One of the most exciting things about rain gardens is the opportunity they provide to plant native species in urban areas, thus helping to restore urban habitat for birds and pollinators like bumblebees and butterflies. We’ve pulled together a list of species that have been used in rain gardens in Nova Scotia and Maine here.

Plant Common Name	Plant Latin Name
Dwarf Goat's Beard	Aruncus aethusifolius
Woods Purple New York Aster	Aster novi-belgii
Blue Flag Iris	Iris veriscolor
Switch Grass	Panicum Virgatum
Hard Sheild Fern	Polystichum aculeatum
Goldsturm Black-Eyed Susan	Rudbeckia fulgida "Goldsturm"
Red twig Dogwood	Cornus sericea
Sweet Flag	Acorus americanus
Swamp Milkweed	Asclepius incarnata
Marsh Marigold	Caltha palustris
White Turtle Head	Chelone glabra
Christmas Fern	Polystichum acrostichoides
New England Aster	Symphyotrichum novae-angliae
Vernal Witch Hazel	Hamamelis vernalis
Native Rhododendron	Rhododendron canadense
Labrador tea	Ledum groenlandicum
Winterberry	Ilex verticillata
Royal fern	Osmunda regalis
Native Columbine	Aquilegia canadensis
Sensitive Fern	Onoclea sensibilis
Cardinal Flower	Lobelia cardinalis
Sweet Fern	Comptonia peregrina
Bearberry	Arctostaplylos uva-ursi
Wild geranium	Geranium maculatum
Northern Maidenhair Fern	Adiantum pedatum
Joe Pye Weed	Eupatorium maculatum
Serviceberry	Amelanchier canadensis
Bayberry	Myrica pensylvanica
Blood root	Sanguinaria canadensis
Wild raisin	Viburnum nudum

When selecting plants, consider its growing preferences and features:

·         Native or non-native?

·         Sun or shade

·         Acidic or alkaline soils

·         Nitrogen fixer?

·         Full-size shape & size

·         Moisture tolerance

·         Edible/medicinal?

·         Wildlife benefits?

The Dalhousie rain garden features:

Sweetfern (Comptonia peregrina)

Serviceberry (Amelanchier canadensis)

Bayberry (Myrica pensylvanica)

Blue Flag Iris (Iris versicolor)

Joe Pye Weed (Eupatorium maculatum)

Black Eyed Susan (Rudbeckia fulgida)

Foam Flower (Tiarella cordifolia)

Christmas Fern (Polystichum acrostichoides)

Ostrich Fern (Matteuccia struthiopteris)

Sensitive Fern (Onoclea sensibilis)

The Evergreen Native Plant Database is a great tool for learning about and choosing native plants. If you really want to be sure a plant is native to Nova Scotia and learn about its natural habitat, consult Roland’s tome, The Flora of Nova Scotia, available online here: Part 1 and Part 2.

It can be a challenge to find sources of native plants, and even as the garden was being planned, some nurseries were closing. Here’s a list of nurseries in Nova Scotia that supply native plants suitable for rain gardens.

Baldwin Nurseries Falmouth, NS 798-9468 www.baldwinnurseries.com

Blomidon Nurseries Wolfville, NS 542-2295 www.blomidonnurseries.net/home

Bunchberry Nurseries Upper Clements, NS 532-7777 www.bunchberrynurseries.ca/

Oceanview Garden and Landscaping Chester, NS 275-2505 www.plantcrazy.ca

Ouestville Perennials West Pubnico, NS 762-3198 www.ouestvilleperennials.com

Dalhousie Rain Garden is Complete!

There’s a new rain garden in town! With funding from TD Friends of the Environment, the Coastal and Water Team at the EAC was able to partner with Dalhousie’s Office of Sustainability to build a rain garden on the Dalhousie Campus.  Our site is a challenging one, in that it receives high flows of stormwater during heavy rains, enough to cause basement flooding of several buildings down the hill toward the Northwest Arm. The garden is located at the intersection of Coburg Rd and Oxford Rd, at the School of Social Work ‘house-turned-office’.  While our goal was initially to build a rain garden that demonstrates that this is an accessible DIY project for homeowners, this site and the design it required moved the project out of the DIY category!  However, there are many aspects of the design and build process that still apply to a homeowner excited about a rain garden sized for capturing rainwater from a roof via a downspout or two.

Our Process & Design

First, we assessed the site, which means that we looked at a variety of factors that will influence how water moves over the site. This includes soil type and drainage properties, slope, and the size of the rain catchment area. Check out previous rain garden how-to posts here for details on these steps.

Our calculations showed that we needed a very large garden to absorb all the stormwater which we calculated flowed onto the site. In fact, the calculated area was larger than the area we had available! In addition, we found the slope of the site to be steeper than the suggested 12% for rain gardens in even the flattest area. This meant that we had to increase the capacity of the garden not by surface area, but by depth. The garden is 24 inches deep, whereas most rain gardens are 6-8 inches deep. To increase the porous volume in the garden, we filled the depression to a depth of 14 inches of clear stone, which would hold water in the bottom of the garden, while also holding soil on top. The cross-sectional design looked much like this diagram, from the Fairfax County Virginia website (Figure 1).

Figure 1. Approximate cross-sectional view of the rain garden at Dalhousie.

We used drainage tile (underdrain in the diagram) to move the stormwater that flows from the road and sidewalk over the steep hillside into the rain garden. See the photo below (Figure 2).

Figure 2. In the middle of this photo, the drainage tile is sticking out of the clear stone in the middle of the garden. The tile extends back to where the volunteers are sitting on the slope to catch water flowing down the slope and direct it into the rain garden.

In this photo (Figure 2) you can see how deep the garden is and just how much clear stone is at the bottom. And another key design feature is starting to form: the berm! The berm is essential in a garden of this size, on this slope, and so close to the house. The berm will help retain the water in the garden while it pools and infiltrates. Below (Figure 3) you can see how the berm has been planted with larger native shrubs such as sweet fern and bayberry, as well as a serviceberry tree. As these plants establish, they will help anchor the berm in place. To increase the strength of the berm, it was constructed out of sod mats from the beginning of excavation. Each layer was tamped down, and then new sod was staked into the backside of the berm all the way around the edge of the garden.

Figure 3. The depth of the garden, the volume of clear stone and the berm are all clear in this photo.

Another unique feature of the garden can be seen from the photo (Figure 4) of the completed garden below: the centre of the garden is actually filled with clear stone and then beach stone all the way to the surface. The goal of this design is to allow water which rushes down the slope from Coburg Rd to first hit the beach stone, which will slow down the flow. Then it will make its way to this holding pond in the centre, and as that space fills, the water will first infiltrate horizontally into the soil and plant roots, and then only when it is really full will the water flow over the surface of the mulch and soil, up to the height of the berm. The water will be slowed to the point where it can infiltrate into the groundwater.

Figure 4. The back portion of the completed garden contains stone all the way to the surface, with native shrubs planted in the berm.

Stay tuned to the blog over the coming weeks to learn more about the plants we used and how we chose them, as well as thoughts about rain gardens functioning as marine protective areas, coastal erosion prevention tools, and social activities.

The Urban Stormwater and Aquifer Improvement Project

Great news!  This year, the EAC has launched a project in Porters Lake aiming to explore innovative stormwater management practices in new residential developments.  The project will involve collaborating with the local community and discussing water, stormwater management, and building healthy water neighbourhoods. We will share results from our pilot site, a new development that is implementing low impact development practices.  We will be monitoring groundwater levels and surface water quality around this new development as it is built and during ongoing construction.  This project is an exciting collaboration between an environmental organization, a developer, university and a community to explore how innovative stormwater management techniques can improve groundwater availability and surface water quality.  We are very proud to share this project with you.

(Photo: during a site visit the team stopped by Bell Lake- Jenny and Rob from the Centre for Water Resources Studies (CWRS), Kyle from genivar, Jocelyne from the Ecology Action Centre (EAC), Brad from Seven Lakes, Rick from CWRS, and Jennifer from the EAC).

Public Outreach

Our project is focused on the Porters Lake area, and we want to connect with this community on freshwater issues.  To share information on these topics, we will launch a series of talks in Lake Echo, Porters Lake, and Musqodoboit in fall 2013 and winter-spring of 2014.  Topics include "Healthy rainwater on your property", "How do we know a lake or stream is healthy?" and "Building a healthy water neighbourhood". Dates and locations for the fall talks are nearly confirmed, so stay tuned to this site so you can attend these events.  Stay tuned for more talks and events in the winter and spring of 2014!

Community Showcase

Bell Lake, in the community of Porters Lake

The EAC believes that seeing is believing, and we have the rain gardens, stormwater demonstration sites and living shorelines to prove it!  The EAC is keen to be working with a developer in the Halifax Regional Municipality using low impact development and open-space principles in their planning.  The Villages of Seven Lakes are in the beginning stages of development in the Porters Lake.  We encourage you to explore their website to find out about their design ideas which include 60% open space, clustered communities, rain gardens, bioswales, and infiltration areas for managing stormwater, innovative stormwater management systems, wetland restoration, tertiary wastewater treatment and many more interesting features.

Research

We are very fortunate to work with a developer that is keen to have ongoing monitoring of their development on lakes and groundwater near their sites.  We have partnered with the Dalhousie Centre for Water Resources Studies who will help us understand the natural conditions of lake and groundwater before homes and roads are built.  They will generate digital models of the site and the impact it has on the surrounding water systems.  These impacts will be compared to that of a conventional development using computer modeling.  This is the beginning of a long and beautiful relationship that will help us understand and hopefully promote low impact development practices elsewhere in HRM and Nova Scotia.

We would love to know your thoughts on stormwater in your community and on your property.  Consider taking our short survey to help us learn more!

Stay tuned for updates on this project, and for information on upcoming talks.

Dig It: Digging tips for your Rain Garden

Before Digging

            There are a couple steps you should keep in mind before you start. If you have currently have grass in that area, it would be easier to kill it first. You can either break it apart manually, or cover the space until the grass dies. The other important thing to consider is whether there are utilities running through that sector of the yard. It is much easier to call the municipality and check that there are no lines running through your property than pay for damages. 

To construct the garden, you will need the following: a tape measurer, shovels, rakes, trowels, carpenter’s level, wooden stakes at least 2 feet long, string, river stones. You will also need topsoil, mulch, and possibly grasses for the berm. From there you can add ornaments, decorative stones, or whatever you wish to improve your garden’s aesthetics. Residential gardens typically cost 3-5$ per square foot to install if you are not paying for labour. The plants chosen to occupy the garden are the most expensive portion.

 The Digging Process

 Outline the perimeter of your rain garden with string.  Now put stakes along the uphill and the downhill side of your garden approximately 1.5 meters apart (5 feet). Now tie a piece of string to the stake pairs and make sure that it is level, that way you can get a consistent depth measurement for the rain garden.

            Start to dig at the uphill stake until you reach the targeted depth you calculated before. Then move down the slope to the downhill side, digging and filling to reach the targeted depth. If you do the one section at a time, it is easier to use the displaced soil to level out the lower end of the garden and start outlining the berm with the surplus. Try to keep the base of the garden as level as possible.

            If you want to line the base with compost, add one or two inches to your target depth. Once you have the garden base dug, mix the compost with the soil at the bottom. If you want to add sand pockets to help filtration, do so now.

            Depending on the distance from your downspout to the garden, you may need to dig a shallow funnel to direct the flow. The side where the water enters the garden is the inlet. Inlets are susceptible to erosion because of the fast-moving water, so you should add larger, rough-edged river rocks to break the flow.

The Berm

            Heap soil around the garden, leaving the entryway bare and ensuring that the highest wall is at the downhill edge of the garden. Make the berm about 0.3 m (1 foot) across and stomp on it hard to make it compact. The berm should have very gently sloping sides to slow erosion and allow water to soak into the ground. To help the water to soak in, you can cover the slopes with mulch, grasses, or dry-tolerant plant species. If you expect to collect large volumes of water at a time, you can include a notch (a low point) in the berm that will allow water to pass during heavy rain events. Line the notch in landscape fabric and add river stones to slow the exit of the water. Angle the outlet away from structures and towards vegetation if possible.

How big should your rain garden be?

Rain gardens typically range from 30-90 square meters (100 to 300 square feet). They can be smaller or larger depending on your resources. Even if you reduce the recommended size of your rain garden by 30%, you will still control 90% of the runoff.

If your rain garden site is within 9 meters (30 feet) of a downspout, most of the storm water will come from the roof so you will only need to calculate its area to obtain the capacity. The area of the roof is the same as the area of the first floor. If you do not know it, use a tape measurer to find the length and width of your house. The product of the two is your area. Now take a walk around your house, how many downspouts do you have? Most houses have 4, each taking care of 25% of the roof runoff. By the shape of the roof, estimate the percent of water your downspout is responsible for. Now multiply the percent of water flowing down the downspout by the roof area. That is your roof drainage area.

Example: You have a building that is 5 m long and 5 m wide and has 2 downspouts that share the load equally. The ground floor area is: 5 m x 5 m = 25 m². If your 2 downspouts are equal, one will take care of 50% of the water. Your drainage area will then be: 25 m² x 0.5 =12.5 m²

If the site is over 9 meters away from a downspout you will need to consider drainage from the lawn. From your rain garden site, look up towards the house and identify which parts of the lawn slope towards your garden. You will need to measure the length and width of the uphill lawn and multiply them to get the lawn area. Now you simply need to add that lawn area to the roof drainage area (calculated in the previous step).

Example: Your building is surrounded by a lawn that slopes towards your garden. It measures 2 m long and 3 m wide. 2 m x 3 m =6 m² as your lawn area. Your total drainage area will then be: 12.5 m² + 6 m² = 18.5 m².

Now you need use your slope, drainage area, and suggested depth to get the surface area of your garden. Use the table below to determine your size factor, then multiply it by your calculated drainage area.

Location	Depth	Sandy	Silty	Clay
Within 9.1 m
	8-13 cm	0.19	0.34	0.43
	15-18 cm	0.15	0.25	0.32
	20 cm	0.08	0.16	0.20
Beyond 9.1 m	All Depths	0.03	0.06	0.10

Example: You have a drainage area of 18.5 m²  sandy soil, and a depth of 8-13 cm. The surface area of your rain garden should then be: 18.5 m² x 0.19 = 3.5 m².

Once you calculate the size of your rain garden, you can divide it by the intended width to find its length. You will want the garden to be twice as long as it is wide, with a max width of 15 feet especially for slopes greater than 8%.

Slecting the Best Site for the Rain Garden: Slope and Soil

Before you get started on building your rain garden, you want to know the answer to two basic questions: "What's my slope?" and "What kind of soil do I have?".  This article will help you get to the bottom of these two questions.

What’s My Slope?

 To calculate the slope of the intended rain garden, pound one stake uphill of the site and the other at the downhill end approximately 5 m (15 feet) apart. Tie the string to the stakes and make sure it is horizontal with a carpenter’s levels. Once the string is properly secured and level, measure the length of the string between the two stakes and then the height of the string from the ground at the downhill stake.   The percent slope will be equal to:

Percent Slope = Height x 100

                         Length

Slope <4%, easiest to build 8-13 cm (3-5 inch) deep rain garden.

Slope 5-7%, try to build it 15-18 cm (6-7 inches) deep.

Slope 8-12%, build it 20 cm (8 inches) deep.

If the slope is greater than 12%, it would be easier to install a garden elsewhere.

How Do I Know What Kind of Soil I have?

Before you even think of putting a shovel in the ground, you also need to figure out what type of soil your rain garden site has. Sandy soils have the fastest infiltration; clay the slowest. Sandy soils are described as gritty and coarse, silty as smooth but not sticky, and Clay as sticky and clumpy. Clay garden must be bigger to handle infiltration and should have sandy pits installed in them to help infiltration. Here is an easy test to help you see if your rain garden will work well at your selected spot:

Soil test: Dig a hole 15 cm (6 inches) deep and fill with water and allow it to filter away. If it takes more than 24 hours to drain, the soil is more clay-based and is not good for a rain garden. You can mitigate the lack of drainage by adding sandy soil pockets during installation, but that takes time and money.

Planning the Rain Garden

The first thing you need to know is where the water goes. Where do the downspouts from your gutters point? Do you see small rivulets of water passing through the grass? Do they join the stream from the downspouts? Does the water pool anywhere? Where can you catch the most water?

This downspout allows stormwater to flow away from the property.

Once you have an idea of where the water flows, you can start eliminating areas around your house. Do not install a rain garden where the water naturally pools, that is where filtration is slowest; think about installing it where the rain garden can catch the water before it pools. You also want to avoid large tree roots. If there are branches overhead, there are roots beneath your feet.

Try to put the rain garden close to a downspout but it is important that you keep the rain garden at least 3 meters (or 10  feet) away from the building to protect the foundation of your house. It is also important to keep your rain garden at least 7.6 meters (or 25 feet) away from your septic system.

After that, it is more a matter of practicality. Installing a rain garden in a flatter portion of land will be easier to dig and level. Make it easier for yourself and do not decide to dig a rain garden where the slope is more than 12%, you will need retaining wall or a high berm to keep the water in and it will take a lot of earth to level out the garden.

In terms of design, crescent-, kidney-, or teardrop-shaped gardens work well. You will want the longer side of the garden to face upslope. Water will hit the berm at the back of that long line, and then flow back towards the garden like a receding wave at the beach. A larger surface will catch the most water possible.

Consider the height, bloom times, colours, and textures of the plants you are planning to use. By choosing plants that bloom at different times, your garden will have a longer flowering season. If you want a traditional, more formal look, try clumping individual species in groups of 3-6 plants and repeat the pattern throughout the garden. Try mixing sedges, rushes, and grasses with flowering species to keep the root network strong and keep some plants from overpowering each other. 

What is a Rain Garden and Why build one?

Rain gardens function as a stormwater absorption and filtration site.  They are beneficial to the local environment by improving water quality and absorbing excess runoff. Rain gardens function by directing stormwater into a plant-filled channel or shallow depression filled with a variety of native plants.  A berm or raised edge at the lower end of the rain garden prevents the water from spilling out.  This allows the water to slowly filter into the soil instead of running out into the streets and down storm drains.  Besides all these environmental benefits, they are beautiful and for the most part they water themselves!

What are the benefits of a rain garden?

• Absorbs 30% more water than a patch of grass.
• Helps reduce stormwater runoff.
• Enhances the aesthetic appeal of your property
• Provides habitat for birds and other critters.
• Recharges groundwater aquifers
• Improves the water quality of your community.
• The plants’ root networks will stabilize the soil on your property and reduce erosion.
• Plants provide a buffer to winds, acting as wind-break for your property.

These photos show the stages of construction of a rain garden.  This rain garden was built in September 2012 at the George Dixon Centre in the North End of Halifax.

For an overview of rain garden, please visit our previous article on rain gardens

Video from Demonstration Site Launch

Our volunteer videographer, Colin MacDonald, put together this video for us from the launch of the stormwater management demonstration site in November 2012.  Take a virtual tour of the demonstration site  by watching this short video.

You can have a look around the stormwater site any time, it is located at fire station #2, 5988 University Avenue, on the corner of Robie Street.  Guided tours will be available when the snow melts and the rain starts flowing, dates will be posted to this blog.