Rain Gardens

Design tips for Homeowners

Rain gardens are shallow depressions in residential landscapes used to capture and cleanse stormwater runoff. They are intended to be beautiful landscape elements that improve water quality. However, most rain gardens are poorly designed, which leads to messy patches of water-logged soil. Plan your rain garden carefully using these best practices.

What are rain gardens anyway?

Rain gardens are similar to bioinfiltration/bioretention basins in function, but their cross section is simplified for the homeowner. Effective infiltration relies on proper contouring of the land, correct runoff calculations, and plant and soil mixes. Engineering techniques have been developed for all of these, but most of them are developed for larger scale applications and not appropriate for your suburban yard or urban courtyard. You will find many diagrams online of rain gardens drawn in cross section with large volumes of soil excavated and replaced with an engineered soil. Typically, a perforated drain pipe is located at the bottom of the engineered soil mix. Engineered soils and perforated drain pipes are best management practices for areas with higher water volumes (i.e. collection from a large parking lot or city street), tighter spaces (i.e. urban streetscapes), and are usually a component in large urban stormwater management systems. You, the homeowner, do not require such large infrastructure to turn a portion of your yard into a rain garden. Think of a rain garden as simply a garden bed designed to accept water runoff from your roof, patio, or driveway.

Many residential rain gardens are not successful aesthetically. I think there are too many bad demonstrations of rain gardens that are overgrown and not functioning properly. I want rain gardens to become more widely accepted as a practice that can improve water quality. To do so, we need more options for the expression of rain gardens. That means we need more styles and types that can work in different places.

Here are design considerations for creating beautiful rain gardens in any setting.

1. Plant Density. Giant beds of mulch with sparse plants are not beautiful. This type of low-density planting is usually done as a cost-saving measure with the intention of “filling in” over time. I think it’s unnecessary and the rain garden (or any garden for that matter) is best when it is planted with dense swaths of plants. Dense planting allows for a plant community to begin functioning immediately and will show long-term resilience in drought and flood. It also fills in to create a lush massing of plants. No large mulch areas will show and the garden will not be as susceptible to weedy invasive plants. Work with your local nursery or landscape contractor to source plants that are smaller in size (plugs or quart-sized containers) to make your rain garden affordable.

2. Plant composition. A rain garden planting should be designed based on its existing context, climate, and location. Too often, a rain garden is designed to “look natural” with random clumps of plants pulled from a list of recommended species. A plant composition is successful when it is carefully considered based on site conditions of available sunlight, amount of water, and the type of soil present. Secondarily, plant composition must also be intentionally designed based on plant form and color, bloom time and year-round interest. If you need help, hire a garden designer or landscape architect to plan the composition and selection of plants.

3. Edge. An often overlooking component of the rain garden is the edge design. A well-conceived edge creates a look or style that blends the rain garden into its site. An edge may be wild, loose, minimal, defined, shifting, color-based, or delineated by a material change. The edge is a key component for a cohesive design of a successful outdoor space.

4. Form. Every rain garden does not have to be “kidney-shaped” or a woodland pond look-alike. Actually, the possibilities are endless for the form of a rain garden so long as the proportions allow for enough surface area for infiltration. Get creative and make overlapping squares like a Mondrian painting, or try a long linear bed at the edge of your lawn and woodland.

Rain gardens can be expressed in a multitude of ways. I encourage you to think outside the status quo when designing yours!