Last fall I wrote an article about food forests, and this summer I want to introduce you to another simple, but elegant method of gardening. This method combines water purification, flood reduction and all of the benefits you would expect in a well producing garden, including food, medicines and pollination services and it can be done very inexpensively. Let’s talk about rain gardens.
When we think of our watershed, we often think of brooks, creeks, rivers and so on, but really a watershed is about how water moves and is stored on a given topography. That means that in the built environment, an apartment building or Walmart parking lot are both still a part of the watershed.
What happens when water moves over hard surfaces like parking lots or compacted earth? Nothing much…most of the time pavement or concrete is strong enough to stand a good deal of surface water flow. Water hits the surface, moves over it and continues to run downgrade; often, picking speed as it goes and potentially getting warmer at certain times of the year as heat is absorbed from paved surfaces. When that same rain water flow hits unpaved surfaces that are not covered in plants, erosion can happen at a rapid rate. Water continues to move down (now carrying soil with it) and causes lowland flooding.
In our hardscaped, built-up and generally paved-over urban environments, these absorption surfaces are often missing and flood water is directed into storm drains and concrete culverts. Water that moves over hard surfaces accumulates road salts, petrochemicals (oil, diesel and gasoline, asphalt residue) and a variety of other vehicle fluids and chemicals.
Organic matter and bacteria in water can be treated fairly easily, but cleaning water of chemicals and heavy metals is an extremely difficult and expensive task. Many municipalities cannot treat stormwater and it is eventually moved back into larger rivers and waterways. When storm water is directed into the same system as sewerage treatment, the system can be quickly overwhelmed in extreme weather events, which can lead to serious public health issues.
The movement of water is one of the most powerful forces on that planet and you can see that those who live on the lower levels of the watershed live with the consequences of how healthy the upper reaches of the watershed are. The YouTube channel Practical Engineering has a great video that discusses urban rainwater management.
Nature has solutions for managing overland flooding. The method is simple: use grasses, perennial plants with deep roots, trees and preserve wetland and riparian zones (the edges of watercourses) where they occur naturally. Lots of organic matter makes for soft surfaces for rain to fall on and roots provide an incredible amount of stabilization against erosion, while using rainwater for their own growth. Natalie Deseta, Project Coordinator with the Nashwaak Watershed Association says that, “Soils rich in organic materials act as natural sponges, absorbing up 20 times their weight in water”. The rainfall that is taken into this “sponge” can percolate deeply into the soil, recharging ground water for drinking.
When it comes to rain gardens, you can make planting choices to suit your own needs and preferences.
The Nashwaak Watershed Association has built two rain gardens since 2019 and both contain hardy, native or naturalized species. Deseta explains, “Depending on the site, water-tolerant native plants that don’t mind getting their feet wet are an ideal option for rain gardens. Native flowering plants are in sync with the local climate and pollinator species. As such, they are lower maintenance than more exotic plants. Native vegetation is also more drought, and flood tolerant.”
She adds, “in our current biodiversity crisis, birds, bees and butterflies are having to travel ever greater distances for food and shelter, as modern, manicured gardens are effectively barren. This results in habitat degradation and fragmentation for these vulnerable species.Planting a variety of vegetation in your yard that flower at different times of year will ensure a steady food supply for pollinators from spring through fall. It will also make for a more attractive rain garden.”
When planting native species, select those that grow in environments similar to your property. For example, forest plants like trilliums are not likely to do well in the full-sun with lots of wind. For meadow like areas, plants like forget-me-not and flocks are a better choice. Pick plants that grow in a range of conditions (very wet to very dry). Some wild plants have one or more parts that are poisonous (or at least cause digestive upset when consumed). If you have pets or small children around, this is a good thing to research.
Lastly, but very importantly, native plants need to be harvested sustainably. You can reach out to local naturalists to get help with this. Digging plants up without having the appropriate knowledge can damage delicate ecosystems and also move invasive species around. In the Fredericton area David Smith with Save A Native Plant is a very good resource and he does have some sustainably grown plants available throughout the year. You can reach David at firstname.lastname@example.org.
You can plant a variety of other things in your rain garden including perennial nursery plants. If clean rain water is coming from a roof, you could grow perennial herbs, vegetables, berries and even mushrooms. If water is coming from a paved surface, it may be contaminated and it should not be used for growing food.
When selecting a place for a rain garden, observe where water moves across your land during a heavy rain. If it hasn’t rained in a while, have a look to see if there are any trails that have left erosion. Most of us will either have rain moving across a paved driveway or from the roof of our home and outbuildings. People that live on steep hills or in low areas may experience seasonal flooding in many places (think the water that always finds its way to the basement).
Once you know where water moves across your land, you can plan where to locate your rain garden. The garden can be varying sizes (depending on the space you have). Creating a longer, narrower garden can be helpful in most cases.
Measure out your garden shape with some stakes (it can be harder to dig in a straight line than it would seem). Remove the top layer of sod and set it aside. Dig down at least the depth of the shovel head and turn to loosen the soil. Remove as much rocks and debris as you can. You should have a nice “double-dug” bed with soil on top that you can easily dig your hands into. If you are finding a lot of clay, do your best to break up large chunks.
Add in manure, compost and soil amendments of your choice (bone meal or blood meal can be helpful or sea kelp if you don’t want to use animal products). Level the soil out with a rake and your bed is ready for planting. Add your plants in and cover with a layer of mulch like wood chips. It would be great to get around six inches of mulch down. Even if you don’t mind weeding, the mulch is necessary to absorb the impact of water flow. Think of your rain garden as a big, beautiful sponge!
Lastly, if your rain garden isn’t close to a building you can make it into a “swale” by taking the sod, flipping it upside down and setting it around the outside edges of your bed. This creates a “berm” that keeps water from flowing out of the bed.
The force of rain directly from the roof is hard on plants (it generally beats them down until the die). If you don’t have an eavestrough or rain gutter that can direct the water into the bed at or near ground level, just plant 8-12 inches out from the dripline. If your soil is often already waterlogged or drains poorly, don’t put your bed directly beside a building, directing water to 10 feet away should be adequate. You don’t want water to stay around your foundation.
If you are really good at bartering and finding garden materials, you could build your garden for free. You can reach out to local arborist companies and often get free mulch. My estimate of cost for a 24- foot-long bed with 15 plants and all supplies purchased is about $200. I recommend buying mulch in bulk (if you have a truck to move it). The bulk cost is about a fifth of the price of an equivalent amount of bagged mulch and no plastic goes to landfill.
Since you will be using perennial plants, the yearly maintenance of rain gardens is not great. Weed as needed, reapply compost, mulch and do some occasional watering if drought conditions are happening. You can relax and enjoy your new landscaping and feel satisfied that you are supporting a clean and healthy watershed.
For regional resources you can connect with EOS Eco-Energy in Sackville/ Tantramar, the Nashwaak Watershed Association and the Kennebecasis Watershed Restoration Committee to name a few. If you have questions about how to install a rain garden or are having trouble finding local resources, you can email email@example.com.
Amy Floyd lives in Taymouth and is a community researcher working on food security and rural issues with the Raven Project (Rural Action and Voices for the Environment).