Right as Rain: Successful Rain Gardens

Right as Rain: Successful Rain Gardens

If you’ve ever trudged through a wet spot in your garden, your boots making that unmistakable sucking sound with every step, or watched the rain cascade off your roof or down your driveway then swirl into the sewer, you may have wondered: How can I channel stormwater runoff to my plants instead?  

A rain garden can be both a practical and attractive answer, with benefits extending far beyond your own backyard.

Getting a rain garden right may take a little planning and some exertion (not to mention fun), but the rewards are worth every effort.

Like a Sponge

Rain gardens typically use native plants with deep root systems to absorb and slowly release excess water. That keeps precipitation from overwhelming storm drains and potentially causing flooding. Rain gardens can also prevent erosion. And as water travels through the rain garden’s soil and plant roots, pollutants and sediments are filtered out, meaning the water that eventually replenishes the groundwater supply is cleaner. 

Rain gardens aren’t a substitute for good drainage, of course. You can’t expect to just place some plants in a water-logged low spot and hope nature will do its level best. 

But, strategically located and properly designed, they can help you hold the line on irrigation, avoid water waste, and improve the environment.

Location, Location, Location

Just like they say in real estate and retailing, location is everything when it comes to rain gardening. 

Though a rain garden can work on flat ground, locating it downslope from the areas where rainwater runoff occurs allows the water to flow naturally into the garden bed. If you can’t quite get into the perfect spot, you can direct runoff toward the rain garden using swales (shallow, elongated ditches with gently sloping sides) or gutters. However, you should avoid placing your rain garden on very steep slopes where erosion might be a concern. And it probably goes without saying that you should avoid placing your rain garden in low-lying areas that already experience poor drainage or collect standing water after a downpour. 

Don’t forget to take sunlight into consideration. While some rain gardens can tolerate more shade than others, most plants suited for them prefer at least partial sunlight for several hours a day. 

It's also good advice to maintain a safe distance from your house foundation (usually 10 feet or more) to prevent water from collecting and causing foundation problems.

Size Doesn’t Matter — Much

Where size is concerned, you don’t have to go big to have a big impact. The size of your rain garden depends on the amount of runoff you want to capture. While county extensions and other experts provide various formulas for determining the ideal dimensions, a good rule of thumb is this: Your rain garden should be 10% of the size of the area draining into it, which means even the smallest garden can work, as long as it can handle the volume of runoff from your roof or paved areas.   

As far as shape, there are no hard and fast rules. However, many rain gardens are kidney- or bowl-shaped. Kidney shapes are popular because they look more natural and freeform (and allow for the efficient use of space), while bowl shapes allow for deeper areas in the center to hold more water and shallower edges for different plant varieties.

Balancing Act

To fulfill their purpose of holding and slowly infiltrating captured water without becoming urban swampland, rain gardens depend on good drainage. 

Poorly draining soil causes water to pool in the rain garden, not reaching the groundwater supplies efficiently and possibly leading to root rot and other perils, like mosquito breeding. 

On the other hand, some moisture retention is also crucial. Plants need water to survive, and the rain garden needs to hold enough water to sustain them between rain events.  Sandy soil drains very quickly and might not retain enough moisture for plant growth.

If your native soil isn’t the ideal sandy loam (best because it combines sand for drainage and silt and clay particles for moisture retention), all is not lost. You can amend heavy clay soils with sand or compost to improve infiltration and add a layer of gravel or crushed rocks underneath (consult with a professional before taking that step). Or consider creating a raised rain garden bed filled with the appropriate soil mix — one that blends loam, sand, and compost. 

The Fun Part

Once you’ve got your rain garden bed set up, the fun starts: picking plants compatible with your rain garden’s conditions. 

Selecting appropriate plants for your rain garden is essential for its success and beauty. Before you head to the garden shop, think about:

• Climate. Select plants native to your region or ones that thrive in similar conditions. This ensures they are adapted to your rainfall patterns and temperature fluctuations.
• Moisture needs. Some plants require consistently moist soil while others tolerate drier conditions. Choose a variety of plants with different moisture needs to create a balanced system.
• Height and spread. Think about the mature size of the plants and space them appropriately. You want to create a layered look with taller plants in the back, mid-sized plants in the middle, and low-growing groundcovers in the front.

Plants often seen in rain gardens include:

• Spring or early bloomers
• Columbine (Aquilegia canadensis)
• Virginia bluebells (Mertensia virginica)
• Trillium (Trillium grandiflorum)

• Mid-season or summer bloomers 
• Bee balm (Monarda didyma)
• Coneflower (Echinacea purpurea)
• Black-eyed Susan (Rudbeckia fulgida)

• Fall bloomers
• Goldenrod (Solidago canadensis)
• Asters (Aster novae-angliae)
• Joe-Pye weed (Eupatorium purpureum)
• Grasses
• Switchgrass (Panicum virgatum)
• Little bluestem (Schizachyrium scoparium)
• Sedges (Carex spp.)

By keeping these factors in mind and choosing suitable plants, it won’t be long before you’ve got it right, and you’re singin’ in the rain garden.